Combinatorial screening methods for metal catalysts and cyclometalated iridium and platinum complexes with non-innocent ligands

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Content COMBINATORIAL SCREENING METHODS FOR METAL CATALYSTS
AND
CYCLOMETALATED IRIDIUM AND PLATINUM COMPLEXES
WITH NON-INNOCENT LIGANDS
by
Bhavna Hirani
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(CHEMISTRY)
May 2007
Copyright 2007
Bhavna Hirani
ii
Dedication
Dedicated to my undergraduate research advisor,
late Dr. (Mrs.) Pushpa Bajaj
iii
Acknowledgments
Over 20 years ago when I was in the middle of my undergraduate program at the
Indian Institute of Technology in Delhi (IITD), I wanted to get a higher degree in
business/hotel management. Towards the end I worked on a research project under
the guidance of late Dr. (Mrs.) Pushpa Bajaj. This research later won me a student
award at the national meeting of American Association of Textile Chemists and
Colorists (AATCC), which was later donated to IITD and is now used as a research
award for undergraduate students. Madam (as we called her) Bajaj’s devotion to
research in science and technology changed my outlook on long-term research
career. She shared with me the joy of discovering and exploring new fields. I am
glad that she visited me in Japan during my master’s research work. It helped keep
my interest alive in research. Thank you, Dr. Bajaj, for being my inspiration.
Here at USC, I can still remember the day when I first met Professor Mark
Thompson. He talked about different areas of his research and showed me the
instrumentation, which looked very fancy at the time. In the end he pointed out that
if I wanted to work in a nicer, new and clean environment, I would be happier with
an advisor in the Loker Hydrocarbon Institute building. And he sure was serious.
There is not a single public elevator in the building to climb up to his lab on the 3
rd
floor! I took some time to decide on my research advisor but I am so glad at the
choice I finally made.
iv
Mark is a great advisor and a great individual. There are no simple words to thank
him enough for his constant support and care during my six years with him. There is
not that many people in academia, like Mark, that can truly support a graduate
student with three little children. For my research, I wanted to work on one subject in
greater depth but in the end I am happy at the way I was exposed to different projects
in the group. It has helped me explore and gain experience in different areas of
chemistry. From Mark, I have learned to respect knowledge, even more and to
respect others who are in the process of learning. He has shown me the path to
learning and sharing knowledge. I wish to thank you, Mark, for your guidance,
patience and understanding, throughout. I hope I can try to be an individual like you.
I appreciate the support of my committee members, Dr. Robert Bau, Dr. Thomas
Flood, Dr. Roy Periana, Dr. Gaurav Sukhatme and Dr. Florian Mansfeld. I always
enjoyed my discussions with Dr. Flood on the fundamentals of Inorganic Chemistry.
I would like to thank Dr. Bau and his student, Muhammed Yousufuddin for their
help with crystallography on the iridium and platinum complexes. With Dr.
Mansfeld I have had very valuable discussions on electrochemistry. I want to thank
him for his support in use of instruments in his group.
I am incredibly fortunate to have found a nerdy scientist and a good friend in Dr.
Mika Nystrom, a researcher in Computer Science at Caltech. He happened to see the
thermal images on my husband’s (his colleague) computer and shared his ideas on
v
improving the technique by building a method based on his knowledge of electrical
engineering. We worked together to produce a screening method that brings in a
sense of achievement in me. I enjoy with Mika, as there is always something new to
learn in the time I spend working with him. He seems to be very learned in all fields
and still an avid learner. I even picked up some chemistry from him!
Two others from Caltech, or related, who have been extremely helpful are Dr. Jonas
Oxgaard and Dr. Petter Persson. Jonas is a post-doc in Dr. William Goddard’s group
and Petter is now a Professor at Lund University in Sweden. I wish to thank Jonas
for working on the DFT calculations and helping me understand the theory of open-
shell molecules. He is always so welcoming and polite. I thank Petter, Jonas’s friend
(who I have never met), for the TDDFT calculations and for his patience with an
experimental chemist like me. Without the added input from the above two people,
some of the mystery of my experimental results would not be unraveled.
I thank Dr. Alexandre Dokutchaev for his generous help in start of the combinatorial
experiments using thermal imaging. He was then a post-doc in the Thompson group.
He is a very focused and knowledgeable man, although sometimes hard to get
through with.
I would thank all the Thompson group members, past and current, for their help and
support in day-to-day tasks. I learned a lot from Dr. Bert Alleyne and Dr. Peter
Djurovich, post-docs in the group. To name a few graduate students in the group, I
vi
extend my thanks to Eugene Polarikov for his collaboration in the synthesis of
bridging ligand. I also want to acknowledge Jian Li, a former graduate student, for
helping me get started on the synthesis of near-IR absorbing metal complexes. I am
grateful to Dr. Alex Alexander, who has always been helpful in solving technical
problems.
The staff from the machine shop helped me build the setup for the combinatorial
screening. I am incredibly grateful to Victor Jordan, Don Wiggins and especially, to
Ramón Delgadillo for their precision skills and active participation in my project.
I would like to acknowledge the contribution of Ross Lewis from the electrical shop
for patiently attaching the platinum wires onto the printed circuit board for the
combinatorial screening experiment.
The scanning electron microscopy pictures came with the help of John Curulli (at
USC) and Scott J. Robinson (at UIUC).
I would like to thank Dr. Richard Haasch at the Center of Microanalysis of Materials
at UIUC for his help with the XPS measurements.
I am very grateful to the efforts of Dr. Scott Wilson, X-ray crystallographer at UIUC
on one of the platinum complexes. I appreciate the time he took to work on the
structure and discuss with me.
vii
I thank Dr. Angelo J. Di Bilio at Caltech for his help and discussion on the EPR
experiments. I also thank Professor George Rossman at Caltech for electronic
spectroscopy in the near-infrared region.
I remember the valuable discussions towards the qualifying exam with Dr. Yi Qin
Gao, now a Professor at Texas A&M University and Professor Wilson Ho, at
University of California, Irvine. Both helped me think beyond my own research.
This dissertation would not be complete without the generous help and warm
welcome of Professor Alexander Scheeline at UIUC. He offered space and the use of
instruments in his group and made me feel very comfortable in the new place. I
would like to thank his students, particularly Rebekah Koch, for taking the time out
from her research to help me.
In the end, I would say that I am immensely fortunate to have Anil, my husband
support me throughout the long years of my graduate studies. There are no ‘two’
words to thank him enough for his encouragement in my work and immense patience
and understanding throughout. This dissertation would be impossible without his
support. He helped me with everything - research, household chores and kids. I
received a lot of help from him in using Matlab program. I still remember the day
when he deferred the tenure-track offer by a year just to give me some extra time to
complete experimental work in Mark’s lab. I hope I can support him, to a similar
viii
extent, in his pursuit of tenure at UIUC. Thank you, Anil for always being there,
home or work.
I am very thankful to my children, Sankhya, Mayank and Shashank, for the love, the
warmth, the smiles and for the little hands that help me walk on the path of learning.
I feel a sense of achievement when I see Sankhya enjoying experiments with liquid
nitrogen or dry ice in the lab. She looks forward to the hands-on chemistry in her
classroom that I offer during the National Chemistry week each year. She desires to
be an astrochemist that would make both parents happy. I hope that my children will
excuse me for the times that I have ignored them to finish this documentation.
I would like to thank my parents for their love and blessings and their help and
encouragement in all spheres of life. They are the pillars of my life. They provided
me with the best undergraduate education in the country. I could always count on
their help, especially when I needed it most, getting back to school with my twin
babies.
I also thank the rest of my family, in particular my sister, for their love and
encouragement. I am lucky to have friends who have been very helpful in many
ways. I thank Dr. Deepshikha Datta for teaching me Odissi dance, that would refresh
my mind, and later on introducing me to Jonas for theoretical calculations. I also
thank Dr. Sujata Bhattacharyya for spending long hours decompressing together, and
for giving me some fundamentals in biology. I am really lucky to have found a great
ix
friend, a listener and a supporter in Manju Singh. I enjoy the time spent with Dr.
Deniz Cizmeciyan talking over hot tea about Chemistry and everything else in life. I
am grateful to Dr. Chiradeep Panja for his help with discussions throughout my
Ph.D.
I am thankful to many others whose names may not appear here but have contributed
to my research work in some or the other way.
This research was made possible by grants from Global Energy Photonic
Corporation (GPEC), New Jersey and Final Year Dissertation Fellowship from the
USC College of Letters, Arts and Sciences for the 2005-2006 academic year.
x
Table of Contents
Dedication ii
Acknowledgments iii
List of Tables xiv
List of Figures xv
Abstract xxii
Introduction 1
Chapter 1: Combinatorial screening of metal catalysts for oxidation of water
using thermal output 4
1. Introduction 4
2. Experimental section 11
2.1. Preparation of catalyst library 11
2.2. Microscopic 12
2.3. Spectroscopic 12
2.4. Set up for thermal imaging 13
2.5. Setup of IR Camera 14
2.6. Measurement 15
2.7. Data analysis 16
3. Results and discussion 16
3.1. Preparation of catalyst library 16
3.2. Characterization of metal catalysts 17
3.2.1. Microscopic 17
3.2.2. Spectroscopic 18
3.3. Thermal imaging 20
3.3.1. Estimation of maximum possible error in heating of resistor 20
3.3.2. Optimization of system parameters 22
3.3.3. Individual measurements 24
3.3.4. Combinatorial measurements - Carbon paper as working
electrode 26
3.3.5. Combinatorial measurements - Metal particles as working
electrode 27
4. Summary 29
Chapter 1 References 57
xi
Chapter 2: Combinatorial screening of metal catalysts for oxidation of water
using visual output 59
1. Introduction 59
2. Experimental section 64
2.1 Description of the screening method 64
Version 1 64
Version 2 66
2.2 Materials and Equipment 68
Version 1 68
Version 2 68
2.3 Error estimates 69
Error from the working electrode 70
2.4 Measurement 75
Version 1 75
Version 2 76
3. Results and discussion 76
Version 1 77
3.1 Blank library (no metal catalyst) as reference 77
3.2 Screening of metal catalysts 77
3.3 Screening of electrolytes 80
Version 2 81
3.4 Screening of metal catalysts 82
4. Summary 84
Chapter 2 References 105
Chapter 3: Cyclometalated Platinum and Iridium complexes with non-
innocent ligands 106
1. Introduction 106
2. Experimental section 109
2.1 Materials and Synthesis 109
2.2 Spectroscopic measurements 112
2.3 X-ray diffraction methods 113
2.4 Electrochemical methods 115
2.5 Theoretical methods 115
3. Results and Discussion 116
3.1 Synthesis and characterization 116
3.2 EPR spectra 119
3.3 Electronic spectra 121
3.4 Electrochemistry 122
3.5 DFT calculations 125
3.6 TD-DFT calculations 128
4. Summary 131
Chapter 3 References 148
xii
Chapter 4: Cyclometalated Iridium dinuclear complex 151
1. Introduction 151
2. Experimental section 154
2.1 Materials and Synthesis 154
2.2 Spectroscopic measurements 157
2.3 Electrochemical methods 157
2.4 Theoretical methods 157
3. Results and Discussion 158
3.1 Synthesis and characterization 158
3.2 Electrochemistry 159
3.3 Electronic spectroscopy 162
3.4 Theoretical calculations 164
4. Summary 167
Chapter 4 References 180
Conclusion 182
Alphabetized Bibliography 185
Appendices 194
Appendix A Matlab program for quantitative analysis. 194
Appendix B Crystal data for tpy-Ir-sq. 200
Appendix B-1 Crystal data and structure refinement for tpy-Ir-sq. 200
Appendix B-2 Atomic coordinates (x 10
4
) and equivalent isotropic
displacement parameters (Å
2
x 10
3
) for tpy-Ir-sq. 202
Appendix B-3 Bond lengths [Å] and angles [°] for tpy-Ir-sq. 205
Appendix B-4 Anisotropic displacement parameters (Å
2
x 10
3
) for
tpy-Ir-sq. 216
Appendix B-5 Hydrogen coordinates (x 10
4
) and isotropic
displacement parameters (Å
2
x 10
3
) for tpy-Ir-sq. 219
Appendix C Crystal data for dfppy-Pt-sq. 222
Appendix C-1 Crystal data and structure refinement for dfppy-Pt-sq. 222
Appendix C-2 Atomic coordinates (x 10
4
) and equivalent isotropic
displacement parameters (Å
2
x 10
3
) for dfppy-Pt-sq. 224
Appendix C-3 Bond lengths [Å] and angles [°] for dfppy-Pt-sq. 230
Appendix C-4 Anisotropic displacement parameters (Å
2
x 10
3
) for
dfppy-Pt-sq. 257
Appendix C-5 Hydrogen coordinates (x 10
4
) and isotropic
displacement parameters (Å
2
x 10
3
) for dfppy-Pt-sq. 263
Appendix D Crystal data for pq-Pt-sq. 267
Appendix D-1 Crystal data and structure refinement for pq-Pt-sq. 267
xiii
Appendix D-2 Atomic coordinates (x 10
4
) and equivalent isotropic
displacement parameters (Å
2
x 10
3
) for pq-Pt-sq. 269
Appendix D-4 Anisotropic displacement parameters (Å
2
x 10
3
) for
pq-Pt-sq. 280
Appendix D-5 Hydrogen coordinates (x 10
4
) and isotropic
displacement parameters (Å
2
x 10
3
) for pq-Pt-sq. 282
Appendix E TDDFT data of Ir-sq and Pt-sq complexes. 284
Appendix E-1 Orbital energies (in au) for Pt-sq. 284
Appendix E-2 TDDFT Excitation energies and oscillator strengths
for Pt-sq. 285
Appendix E-3 TDDFT Excitation energies and oscillator strengths
for Pt-sq. 288
Appendix E-4 TDDFT Excitation energies and oscillator strengths
for model system of Pt-sq. 291
Appendix E-5 Orbital energies (in au) for Ir-sq. 292
Appendix E-6 TDDFT Excitation energies and oscillator strengths
for Ir-sq. 293
Appendix E-7 TDDFT Excitation energies and oscillator strengths
for model system of Ir-sq. 300
Appendix F TDDFT data for trans-isomer of Iridium dinuclear
complex. 301
Appendix F-1 Excitation energies and oscillator strengths for trans-
isomer of dinuclear Iridium complex. 301
Appendix F-2 Orbital energies (in au) for trans-isomer of dinuclear
complex. 305
Appendix G TDDFT data for cis-isomer of Iridium dinuclear
complex. 306
Appendix G-1Orbital Energies (in au) for cis-isomer of dinuclear
complex. 306
Appendix G-2 TDDFT excitation energies and oscillator strengths
for cis-isomer of dinuclear complex. 307
xiv
List of Tables
Table 1 Binding energy (BE) and full width at half maximum (FWHM) of the
core levels measured by XPS of the catalyst metal particles supported
on carbon paper. 56
Table 2 The electronic spectra and electrochemical data of iridium and
platinum dioxolene complexes. 145
Table 3 Molecular orbital energy differences (in kcal/mol) in the ground state
of the Ir-sq and Pt-sq
1
complexes. The molecular orbitals that are
involved in low energy charge-transfer transitions (see TDDFT) are
listed in the table. 146
Table 4 Excitations in the Ir-sq and Pt-sq complexes that contribute to the
charge-transfer transition in the red to near infrared region along with
their relative contributions given by the expansion coefficients. The
oscillator strength indicates the strength of absorption at that
wavelength. 147
Table 5 Data from electronic spectra and the electrochemical data of iridium
dinuclear complex and its mononuclear analog. 179
xv
List of Figures
Figure 1 Current-voltage curves from screening of nanoparticles of platinum
group metals supported on carbon paper. Results from individual
metals are shown on top and from combinations of metals are
shown on the bottom. The scan rate is 5mV/s. 31
Figure 2 Toray carbon paper, the surface as seen on SEM and the cross-
section of the fibers 32
Figure 3 Combinatorial setup for infrared thermal imaging of 96
electrochemical cells used for the screening of metal catalysts
towards the oxidation of water. The bottom picture shows the
working electrode (carbon paper supported metal particles)
sandwiched between an aluminum plate and Teflon block with 96
wells. 33
Figure 4 Scanning electron microscope pictures of Pt metal catalyst, on the
surface of a carbon fiber, prepared by thermal oxidation in air
followed by reduction in (i) hydrogen, and (ii) NaBH
4
. 34
Figure 5 Scanning electron microscope pictures of Ir metal catalyst, on the
surface of a carbon fiber, prepared by thermal oxidation in air
followed by reduction in (i) hydrogen, and (ii) NaBH
4
. 34
Figure 6 Scanning electron microscope pictures of Ru metal catalyst, on the
surface of a carbon fiber, prepared by thermal oxidation in air
followed by reduction in (i) hydrogen, and (ii) NaBH
4
. 35
Figure 7 Scanning electron microscope pictures of carbon fibers imaged after
thermal oxidation in air followed by reduction in hydrogen. 35
Figure 8 SEM pictures of iridium catalyst supported on carbon paper. 36
Figure 9 SEM pictures of ruthenium catalyst supported on carbon paper. 37
Figure 10 SEM pictures of platinum catalyst supported on carbon paper. 38
Figure 11 XPS survey scans of (a) Pt, (b) Ir and (c) Ru nanoparticles on the
surface of carbon paper. 40
Figure 12 XPS spectra of the metal (Pt, Ir and Ru) nanoparticles on the
surface of carbon paper. (a) Pt 4f, (b) Ir 4f and (c) Ru 3d and (d)
Ru 3p core levels. 42
xvi
Figure 13 Thermal image shows reflection from (a) aluminum plate and from
(b) metallic ends of the fixed resistors on the array that are in the
field of view of the camera. 43
Figure 14 A thermal imaging experiment for optimization of the magnitude
of fixed resistor in series with the electrochemical cell. Different
values of resistors were used in parallel with each other and in
series with a variable resistor to adjust the amount of current
flowing through the circuit. Rows: row 1 is 1000Ω resistors, row 2
is 270Ω resistors and row 3 is 100Ω resistors. Columns: column 1
is 7mA current, column 2 is 6mA current, column 3 is 5mA
current and column 4 is 4mA current through the circuit. 44
Figure 15 Thermal image that highlights the number of bad pixels in the
infrared camera that was used for thermal output of combinatorial
screening of catalysts towards the oxidation of water. 45
Figure 16 Thermal imaging of a library of Pt and Pd particles with different
electrolytes in varying concentrations. The scan was from 0-5V at
about 45mV/s. The image shown here is at an applied potential of
about 5V. The color bar on the right gives the thermal counts (a
100 thermal counts is equivalent to about 0.1°C rise in
temperature). 46
Figure 17 Linear sweep voltammograms of the different metal catalysts as the
working electrodes of the cell obtained on individual
measurements in the combinatorial setup. The current-voltage
curves from cells with metal catalysts are referenced to that
obtained from supporting carbon paper. The scan rate was 100
mV/s. 47
Figure 18 Thermographs from a blank carbon paper library obtained on a
scan from 0-6V at a rate of 53.5mV/s. A 100Ω array (uncoated) of
resistors was used for 49
Figure 19 Thermal images of a combinatorial library of the blank carbon
paper scanned from 3-6V at a rate of about 35mV/s. A circuit
board with 270Ω resistors was used here. Black paint was sprayed
on it to minimize reflection from the surface. The images are
shown at applied potentials of (a) about 5.8V, (b) 5.5V and (c)
4.7V. The color bar on the right gives the thermal counts (a 100
thermal counts is equivalent to about 0.1°C rise in temperature). 52
xvii
Figure 20 Thermograph of an array containing platinum and iridium metal
catalysts as working electrodes in a series of alternating diagonals.
A dashed line indicates the cells containing iridium particles. The
thermal counts for the pixels on this line are 54
Figure 21 Quantitative analysis of the thermal counts using thermal images
from a combinatorial library containing iridium and platinum
catalysts for the oxidation of water. 55
Figure 22 Automated serial photoelectrochemical screening to characterize
the activity of supported Au clusters for water oxidation and CO
oxidation. The cell containing counter and reference electrodes
traverses the library illuminating each sample and measuring the
photoelectrochemical property. 87
Figure 23 Schematic of the electrochemical control system developed for the
combinatorial electrochemical screening of catalysts of direct
methanol fuel cells. The modules depicted above are the computer
for data acquisition (top), a 64-channel current follower (center), a
potentiostat (bottom left), a triangular sweep generator (bottom
right), and an electrochemical array cell (bottom center). 88
Figure 24 Layout of version 1 of electrochemical combinatorial screening.
The schematic is shown for one electrochemical cell from the
combinatorial experiment. 89
Figure 25 Illustrates the basic principle of screening method that uses a
sensitive digital ammeter electronic circuit. The two input
voltages to the amplifier are shown as a function of time in the top
part of figure. The middle plot shows the rate of output voltage
with respect to the two input voltages. The bottom plot shows the
light intensity from LED as a function of current through the cell. 90
Figure 26 Images from equipment used in version 1 of the screening method.
(a) The 8x12 combinatorial array is shown here in the Teflon
block with 96 wells that hold the electrolyte solution. The catalyst
library on carbon paper is sandwiched between Teflon block and
aluminum plate. (b) Electronic equipment, like the waveform
generator, the sourcemeter and oscilloscope. (c) Top face of the
electronic board with surface-mount red LEDs in a 4x4 array. 91
Figure 27 Layout of the design of system in version 2 of combinatorial
screening method. The schematic is shown for one cell from the
combinatorial experiment. 92
xviii
Figure 28 Images of the three printed circuit boards used to build a sensitive
digital ammeter in version 2 of the combinatorial screening
method using visual output. Board (a) is used to interface with the
electrochemical cell, Board (b) has the potentiostats to measure
current through the cell and Board (c) has the comparators and
LEDs (on the other side) for visual output. A dime is placed on
the boards for estimation of size. 94
Figure 29 Images from the setup used in version 2 of the combinatorial
screening method using visual output. The circuit is complete in
(a) while in (b) the counter and reference electrodes are seen
encased in plastic tubing before lowering into the electrolyte wells
with working electrode at the bottom of the well. 95
Figure 30 Current-voltage curves from individual measurements in
electrochemical cells in the combinatorial setup. The dashed line
is drawn at a current of about 30 µA, where the catalytic activity
is compared in the cells. The scan rate is 100mV/s. 96
Figure 31 Images from screening of a library of carbon paper (TCP) by
version 1 of the method. The potential at which the LED turns
‘on’, is defined as the turn-on potential for the cell at that current
density. A turn-on voltage of 2.82V is obtained for the cells with
carbon paper. The maximum spread observed in the turn-on
voltage of all cells is about ±10mV. 97
Figure 32 Images from screening of a catalyst library of metal particles by
version 1 of the method. The images are at (a) 2.27V, (b) 2.33V,
(c) 2.36V, (d) 2.4V and (e) 2.6V during a voltage sweep from 0-
3V at a rate of100 mV/s. The sequence of catalytic activity
towards the oxidation of water is Ru > Ru/Ir (80/20) > Ir > TCP. 98
Figure 33 Images from screening of a catalyst library of metal particles by
version 1 of the method. The images are at potentials of (a) 2.4V,
(b) 2.5V and (c) 2.8V during a voltage sweep from 0-3V at a rate
of 100mV/s. The sequence of catalytic activity towards the
oxidation of water is Ru > Ru/Ir (50/50) > Ir with reference to
carbon paper. 99
Figure 34 Current-potential (averaged) curves obtained from recording the
values in individual electrochemical cells in version 1 of the
method. The potential is reported versus Ag-AgCl standard
reference electrode. The Ru metal particles have greater kinetic
activity than TCP throughout the scan from 0-3V at 100mV/s. 100
xix
Figure 35 Images from screening of electrolytes, tetramethylammonium
bromide [N(CH
3
)
4
Br] and sodium perchlorate [NaClO
4
] by
version 1 of the method. The images are at (a) 2.3 V and (b) 3.0 V
from a scan of 0-3V at 100mV/s. The oxidation of bromide ion
clearly precedes the oxidation of water. 101
Figure 36 Images from screening of a catalyst library of metal particles by
version 2 of the method. The potential at which the LED turns
‘off’ is measured here vs. Ag-AgCl reference electrode. The
sequence of catalytic activity at a current of 30µA through each
cell is Ir > Ru > Pt > TCP. It is in good agreement with that
obtained from measurements in individual cells using a standard
reference electrode (shown in graph). The voltage was scanned
from 0-1.5V at 100mV/s. 102
Figure 37 Images from screening a library of TCP (Toray carbon paper) by
version 2 of the method. The turn-on potential, at a current of
about 30µA through the cell (red LED), is 1.2V. It is lower at
lower values of current (green LEDs). The voltage scan rate is
100mV/s. 103
Figure 38 (a) Current-voltage curves obtained from individual measurements
in four cells, all containing metal particles as catalyst. (b) The
spread in turn-on voltage (of the order of 15-60mV) at a current of
30µA is evident here. Potentials are reported versus Ag-AgCl
reference electrode. The voltage was scanned from 0-1.5V at
100mV/s. 104
Figure 39 Chemical structures of iridium and platinum complexes. 133
Figure 40 Thermal ellipsiodal views of (a) the tpy-Ir-sq complex, (b) the pq-
Pt-sq and (c) the dfppy-Pt-sq complex. Also shown (d) is the
packing diagram of dfppy-Pt-sq in a unit cell. 135
Figure 41 Low temperature EPR spectra of the iridium and platinum
complexes measured at 80K in glassy toluene. 136
Figure 42 Electronic spectra of tpy-Ir-sq and dfppy-Pt-sq complexes
measured in dichloromethane at room temperature. The molar
absorbance is in units of M
-1
cm
-1
. The inset shows the absorbance
in the ultraviolet region of the spectra. 137
Figure 43 Electronic spectra of pq-Pt-sq and dfppy-Pt-sq complexes
measured in dichloromethane at room temperature. The molar
absorbance is in units of M
-1
cm
-1
. The inset shows the absorbance
in the ultraviolet region of the spectra. 138
xx
Figure 44 Cyclic voltammograms of tpy-Ir-sq, dfppy-Pt-sq and pq-Pt-sq
complexes measured at room temperature. The potentials are
shown relative to the internal reference couple Fc
+
/Fc. The solvent
was acetonitile for the first two complexes, the pq-complex was
measured in N,N-di-methylformamide. 139
Figure 45 Spin densities calculated from the density functional theory method
for the Ir-sq (left) and Pt-sq (right) complexes. There is some spin
density on the metal center but is mostly on the semiquinone
ligand. 140
Figure 46 Naming scheme used in this work for open-shell molecules. 141
Figure 47 Transition energies of (a) Ir-sq and (b) Pt-sq complexes obtained
from TD-DFT calculations shown along with the experimental
electronic spectra. The calculated transitions are shown for both
the model compound and the full molecule. The extinction
coefficient is given in M
-1
cm
-1
. 142
Figure 48 β-molecular orbitals of Ir-sq complex obtained from TD-DFT
calculations. The orbitals for model compound are shown on right
and those for the full complex are on the left. 143
Figure 49 β-molecular orbitals of Pt-sq complex obtained from TD-DFT
calculations. 144
Figure 50 Chemical structure of the iridium dinuclear complex. 169
Figure 51 Synthesis of the bridging ligand in the iridium dinuclear complex. 170
Figure 52
1
H-NMR spectrum of the diamagnetic iridium dinuclear complex
in d-CHCl
3
measured at RT. The bottom figure shows the peak
integrals in the aromatic region relative to the 12 aliphatic protons. 171
Figure 53 Cyclic voltammogram of iridium dinuclear complex in acetonitrile
at a scan rate of 100 mV/s. 172
Figure 54 Cyclic voltammograms of (a) Os dinuclear and (b) Ru dinuclear
complexes in acetonitrile at a scan rate of 200 mV/s. 172
Figure 55 Electronic absorption spectrum of the iridium complex in CH
2
Cl
2
shown in the ultraviolet and visible region. 173
Figure 56 Electronic absorption spectrum of the iridium complex in CH
2
Cl
2
shown in the near-infrared region (red curve) with an overlap of
the peak from the visible region (blue curve). 173
xxi
Figure 57 Electronic absorption spectrum of the dinuclear iridium complex
compared to the mononuclear iridium complex with the dioxolene
type linkage. Both were measured in dichloromethane at RT. 174
Figure 58 Electronic spectra of Ru mononuclear [Ru(bipy)
2
(bsq)][PF
6
] (upper
trace) and Ru dinuclear [B(bipy)
2
(sq-sq)B(bipy)
2
]
2+
(lower trace)
in CH
2
Cl
2
at the same concentration. 174
Figure 59 Electronic spectra of Os dinuclear complex [Os
2
(L
1
)]
n+
(n = 2, 3, or
4), where L = bis-dioxolene bridging ligand, measured during a
spectroelectrochemical experiment in acetonitrile at –30°C.
Spectra of n = 0 and n = 1 states could not be recorded due to
deposition of the reduced forms of the complex on the Pt electrode
surface. 175
Figure 60 The HOMO (left) and LUMO of iridium dinuclear complex in the
trans-configuration. The top image shows the optimized geometry
in the trans form. 176
Figure 61 The HOMO (left) and LUMO of iridium dinuclear complex in the
cis-configuration. The optimized geometry for the cis isomer is
shown above. 177
Figure 62 Experimental electronic spectra (visible to infrared region) and
calculated (TDDFT) transition energies of trans (olive) and cis
(blue) isomers of the iridium dinuclear complex. The experimental
values were obtained in dichloromethane and the calculations
were done in gas phase. The absorbance is in units of M
-1
cm
-1
and
the oscillator strength is a dimensionless quantity that relates to
the molar absorbance. 178
xxii
Abstract
Techniques are developed for the combinatorial screening of metal catalysts towards
the oxidation of water. The electrochemical reaction is thermodynamically feasible
but kinetically labile at the anode. The use of metal particles as catalysts at the anode
can lower the overpotential for the reaction. Thermal output method of combinatorial
screening is explored as a qualitative and fast measurement of activity of platinum-
group catalysts. The activity is monitored as a function of the heat dissipated across a
fixed resistor in series with the cell. The more active a catalyst, a larger current flows
through the cell for the same applied potential resulting in a larger dissipation of heat
across the resistor that is imaged by an infrared camera as greater heating. The
choice of electrolytes is also explored. The preparation of metal catalyst using
thermal reduction of metal precursor solutions is described. The catalytic surface is
characterized by microscopy (SEM) and spectroscopy (XPS).
The set up of instrumentation for a combinatorial array of metal particles for the
thermal output method is described. The optimization of system parameters is listed.
The data is presented qualitatively as thermal images and in some quantitative results
from the analysis of thermal counts. Comparative studies with individual
measurements provide an estimate of overpotential required for oxidation of water.
The limitations of thermal screening method are discussed.
xxiii
Combinatorial screening using visual output, as a more quantitative method than
thermal output, is experimented for the activity of metal catalysts. The method is
based on the amplification of current through the cell such that small differences in
the activity of metal particles can be observed by monitoring the brightness of LED
in the circuit. It is made possible by the use of a potentiostat and an ammeter for
each. It is shown useful in rating the activity of some of the platinum group metals as
catalysts for the oxidation of water. It also compares very well to individual
measurements in the same setup using a standard laboratory potentiostat.
The coordination chemistry of cyclometalated iridium and platinum metal complexes
with a dioxolene-type non-innocent ligand is discussed with interest in tuning the
low-energy transitions. The synthesis and characterization, electronic and
electrochemical properties of these open-shell complexes is described. Theoretical
studies using both density functional methods and time-dependent density functional
methods are given. The iridium and platinum metal complexes are compared through
structural, spectroscopic, and electrochemical properties to related complexes of
ruthenium and osmium.
The electronic properties of an iridium dinuclear complex are studied and compared
to the mononuclear analog. The synthesis and characterization, electronic and
electrochemical properties of the complex is described. The results from time-
dependent density functional calculations are presented as significant to the
discussion on isomers of the complex.
1
Introduction
Oxidation of water or the reduction of oxygen is one of the most important
electrocatalytic reactions because of its role in electrochemical energy conversion,
fuel cells, corrosion and several industrial processes. The reaction continues to be a
challenge for electrochemists because of its complex kinetics and the need for better
electrocatalysts. Oxidation of water is a four-electron reaction and involves the
formation of O-O bond that is of considerable stability. It is very hard to achieve the
thermodynamic reversible potential of 1.229V (versus a normal hydrogen electrode)
for the four-electron reaction that is a very irreversible reaction. Since the reaction is
not kinetically facile there is a significant overpotential that could be reduced with
the use of better catalytic surfaces. Although a mechanistic understanding of the
reaction on many surfaces is not yet detailed, there are considerable insights to the
course of the reaction. The most notable need remains the improvement of the
catalytic activity of the existing and the development of new, better, metal (or non-
metal) electrocatalysts.
Combinatorial screening methods using high-throughput tools have been developed
as efficient means to screen the catalytic activity of metals. The methods are based
on a direct or an indirect output from the reaction. Optical screening using
fluorescence imaging and infrared thermography are two notable screening tools that
2
use an indirect output. Direct measurements in series and in parallel are also used for
combinatorial screening. There are limitations to the range of experimental
conditions using the above methods.
In the first half of this thesis, we describe two combinatorial screening methods that
we developed for catalytic activity of noble metals towards the oxidation of water.
Chapter 1 gives a description of the preparation and characterization of electrode for
the reaction and discusses the results from screening using thermal output. An
infrared camera is used to image the joule heating across a fixed resistor in series
with the electrochemical cell. An active catalyst has larger amount of current through
the cell for the same applied potential and that results in a larger temperature rise on
the surface of the resistor that is imaged by the camera. We were able to identify the
more active nature and concentration of electrolytes and also tell the difference in
activity It works as a good preliminary qualitative screening method but has some
limitations. Chapter 2 introduces a fast, efficient and economical method using visual
output for the screening of metal catalysts towards oxidation of water. This method
is developed to overcome the limitations from thermal output method. The use of a
potentiostat, an ammeter and LEDs for each cell creates a sensitive digital ammeter
that amplifies the current through the cell and results in very sensitive screening of
metal catalysts. This kind of combinatorial approach has not been shown before. A
comparison is drawn in results from combinatorial screening and individual
screening of electrodes in the same setup.
3
The second half of this thesis focuses on cyclometalated complexes of iridium and
platinum with non-innocent ligands. The interest comes from observed low-energy
intense transitions that are redox switchable in ruthenium and osmium complexes.
The dioxolene ligand onto such complexes results in strong mixing of the metal and
ligand frontier orbitals such that the assignment of oxidation states to individual
metal and ligand components is difficult. A wide variety of iridium and platinum
complexes with cyclometalated-ligands have been studied as emissive materials for
organic light emitting diodes. The choice of cyclometalating ligand can help tune the
electronic properties. Chapter 3 of this thesis describes the synthesis and
characterization, electronic and electrochemical properties of cyclometalated iridium
and platinum complexes with a dioxolene ligand. Theoretical calculations are given
for the complexes that bring out some interesting results supporting the experiments.
The commonly talked about use of such complexes as sensitizers in solar cells will
not be likely with these iridium and platinum complexes. Chapter 4 extends the study
to a dinuclear complex of iridium. The extensive delocalization on a bridging ligand
can result in unique metal-metal interactions. The magnitude of these interactions
can be controlled by the conformation of the bridging ligand if it is redox active. The
synthesis and characterization, electronic and electrochemical properties of bis-
dioxolene bridging ligand with cyclometalated iridium centers is described in this
chapter. Theoretical calculations are provided for understanding of the presence of
different isomers and their role in determining the properties of complex.
4
Chapter 1: Combinatorial screening of metal catalysts for
oxidation of water using thermal output
1. Introduction
The splitting of water by electrolysis to generate oxygen and hydrogen gases is given
by the following reactions at the anode and the cathode, respectively.
2H
2
O (l) = O
2
(g) + 4H
+
+ 4e
-
(1)
4H
+
+ 4e
-
= 2H
2
(g) (2)
The thermodynamic potential for the reaction (1) at the anode is 1.229V vs. NHE
(normal hydrogen electrode) and for reaction (2) at the cathode is 0.000V vs. NHE in
aqueous solution at pH = 0 at 25°C. The oxidation of water is a thermodynamically
demanding reaction. It is also mechanistically demanding since it requires the loss of
four electrons and four protons with the concomitant formation of an O-O bond. The
kinetics is favorable for the electrocatalysis of hydrogen at a platinum electrode.
With unfavorable kinetics at the anode for oxidation of water there is a considerable
overpotential required for the reaction. This decreases the efficiency and raises the
cost. There is need for catalysts that can reduce the overpotential by their increased
activity. At the same time, catalysts need to be stable to corrosion caused by the
positive potentials used for electrolysis.
5
Metal alloys are used as heterogeneous catalytic materials for the electrolysis of
water. The elements for alloys usually belong to the platinum group metals. There is
vast variety of combinations of these and other elements (non-noble metals) in the
periodic table that have not been studied so far as catalysts for reduction of
overpotential in oxidation of water. To discover some of the most active and stable
catalysts there has to be a fast, reliable and economical method that can screen a
large number at one time.
Combinatorial chemistry of catalytic materials involves library preparation,
component characterization, property assay and a structural database to manage the
information flow. Large libraries of potential catalysts or materials can be prepared
in a combinatorial fashion. High-throughput screening (HTS) combined with a high-
capacity and efficient informatics system can increase the rate of progress in
combinatorial screening of catalysts.
Some of the high-throughput screening tools used in search of active anode catalysts
for the oxidation of water or the reduction of oxygen have been infrared
thermography, optical screening and electrochemical methods, both in series and in
parallel. A few review articles
1,2,3,4,5,6,7,8,9
in the field summarize the different methods
of screening catalysts. The common approach to screening involves the application
of a bias to an array of electrodes, step up the bias and monitor the current activity to
check which one has a significant current flowing through it first. This is the
electrode with the lowest overpotential for the reaction.
6
The optical screening method has been demonstrated for the optimization of catalysts
for oxidation of water and reduction of oxygen for regenerative fuel cells,
10
for
colloidal oxygen-evolving catalysts,
11
electrocatalysts for enzyme-free amperometric
glucose sensors
12
and for the electro-oxidation of methanol for direct methanol fuel
cells.
13
This method is based on an optical response of a fluorescent dye to changes
in the local pH brought about by the electrochemical reaction. The advantage lies in
the simplicity of a single working electrode, a parallel technique that uses only
aqueous indicator solutions and a hand-held lamp, and the use of a single potentiostat
and current follower for electrochemical control and measurement. The limitations of
this indirect method are the relative insensitivity (signal-to-noise) compared to the
direct measurement of electrode current and the limited range of experimental
conditions (for example, the nature of electrolyte, the pH of solutions) because of the
need of a proton-sensitive dye in the electrolyte. There is the possibility of
adsorption or reaction of dye at the electrode surface that may influence the activity
of the catalyst during screening.
Infrared (IR) thermography has been used for the evaluation of activity in
combinatorial libraries of catalysts. It detects the infrared radiation emitted and
reflected by all objects. A photovoltaic IR camera with a focal plane array (FPA)
detector can deliver a high-resolution two-dimensional thermal image of the object in
focus. The image is a spatial map related to the temperature and emissivity
distribution of the objects in picture. Different colors in thermal IR image visualize
7
different photon intensities of the detected IR radiation. Photon intensities can be
converted into blackbody temperatures of the object either by knowing the emissivity
of a material or through a temperature calibration.
Infrared thermography has recently gained momentum due to the development and
introduction of FPA cameras. The major advantages of FPA cameras compared to
traditional IR scanning thermal imagers are their simpler construction, quicker
reading time, and the fact that pixels are acquired simultaneously (although they are
read sequentially).
14
The main drawback of FPA cameras is that the output is not
calibrated since there is no internal temperature reference source to which the signal
can be referenced. This is the main reason why FPA cameras are used for qualitative
rather than quantitative IR thermography applications.
The advantage of IR thermography is that it is a fast and non-contact technique for
primary screening. The screening time is independent of the sample number on a
library. The data can be visualized directly or processed for quantitative results. IR
sensors can be used to detect, image and measure patterns of thermal radiation that
catalysts emit as a by-product of their activity. Real-time detection and analysis of
temperature profiles enable an exothermic reaction to be monitored in a truly parallel
manner. The catalytic activity of a library can be displayed after careful removal of
the artifacts by emissivity correction. This has been demonstrated for the screening
of heterogeneous catalysts for the oxidation of hydrogen to water,
15
for the catalytic
hydrogenation of hexyne and the oxidation of isooctane and toluene (gas phase
8
reactions),
16
and for the enantioselective reactions mediated by biocatalysts or chiral
transition metal catalysts (liquid-phase reactions).
17
All of the above studies report
the analysis of temperature profiles of exothermic reactions catalyzed by metals or
metal oxides. Temperature differences of 0.1K were clearly resolved after emissivity
corrections.
Real-time observation of temperature rise and thermal breakdown processes in
organic light emitting diodes has been studied using infrared thermal imaging.
18
This
study does not require very high resolution of temperature differences. This was not
a combinatorial study, though.
We propose the use of infrared thermal imaging technique for the combinatorial
screening of metal catalysts towards the oxidation of water. Fluorescence imaging
has been used for screening nanoparticulate platinum group metals on a supported
electrode for the above reaction.
19
It was followed by electrochemical measurements
on a few electrodes resulting in a quaternary mixture of metals as the most active and
stable catalyst. They have shown that a mixture of metals helps increase the activity
and stability of individual metals at the electrode (Figure 1). A large variety of
binary, ternary, quaternary and more combinations of metals should be screened for
potential use as active and stable catalysts. Combinatorial screening becomes
necessary to speed up the analysis of metals and their combinations for catalytic
activity towards the oxidation of water.
9
Due to the limitations of optical imaging, mentioned earlier, we tried the thermal
approach for a parallel measurement. IR thermography is based on measurements of
energy in the infrared portion of the electromagnetic spectrum being irradiated by a
target under inspection. All objects with temperatures above absolute zero radiate
energy and the amount of energy radiated by the object is proportional to the fourth
power of its absolute temperature. Thermal energy radiated from an object can also
be accompanied by thermal energy the object reflects from the environment. The
combined thermal energy is referred to as the thermal energy emitted. It is this
emitted thermal energy, the combination of radiated and reflected thermal energies
that thermal imagers are able to detect. It is only the radiated energy, however, that is
of interest in diagnostic processing.
20
In our experiment (Scheme 1), the IR camera does not directly image the infrared
radiation from the top of the cells because there is quick dissipation of heat into the
bulk. The amount of catalyst on the surface occupies a very small spatial area and
thus the temperature change is very small to be detected in bulk solution. We cannot
monitor the evolution of oxygen and hydrogen gases by infrared spectroscopy
because they are IR inactive.
To modify the array for use with IR camera imaging we introduced a fixed resistance
in series with each of the electrochemical cell circuits (Figure 3). The current
flowing through the cell gives a potential drop across the resistor. The joule heating
across the resistor is directly proportional to the current through the cell. The IR
10
camera images this internal thermal energy radiated by the resistor. The surroundings
are at a lower temperature than the resistors when there is current flowing through
the cell.
Scheme 1
Our combinatorial setup is a 12x8 array of electrochemical cells. The working
electrode (of metal particles) is different from cell-to-cell while the counter electrode
is fixed for each cell. The nature and concentration of electrolyte can be varied from
cell-to-cell.
11
2. Experimental section
2.1. Preparation of catalyst library
Platinum group metal chloride salts were used as starting materials. IrCl
3
was
purchased from Next Chimica and H
2
PtCl
6
, PdCl
2
and RuCl
3
were obtained from
Aldrich Chemical Co. Solutions of 2.5 mM concentration were prepared by
dissolving the metal salt in de-ionized water. To ensure good solubility the solutions
were sonicated for about one hour and a drop of hydrochloric acid was added, as
needed, to adjust the pH to about 2 in order to slow the hydrolysis process.
Toray carbon paper (TGP-H-120, 0.37mm thickness, density=0.49g/cc) [Figure 2]
was used as the electrode substrate for the metal particles. It is made of
polyacrylonitrile fibers placed in a random orientation. It is inexpensive
($0.13/sq.in), conducting (ρ=1.5Ω/cm) and resistant to deformation at high
temperatures. It is easy to handle and is resistant to electrochemical corrosion. It also
has good gas permeability. It was cut into rectangular pieces of 13.4 cm x 9.8 cm and
cleaned by rinsing with acetone and DI water, then dried in the oven at 90°C before
use. A plastic template was used as a guide to deposition of metal salt solutions onto
the carbon paper.
A 10µl volume of the solution was dropped onto each spot on the array using a
repeater-pipette for multiple dispensing. For binary mixtures, in order to achieve the
12
desired composition of the catalyst spot, first component 1 was dispensed at each
spot, and then component 2 was dispensed onto the pre-existing spot containing
component 1. Thus the mixtures were prepared in situ on each spot. The total
number of moles of metal on each catalyst spot was maintained constant. The drops
on the carbon paper were left to dry in air for a couple of hours.
The library containing the metal salts was then calcined in ambient air in a tube
furnace at 430ºC for four hours followed by reduction in H
2
(5% H
2
mixed with N
2
at
a low flow rate) at the same temperature for 4 hours.
2.2. Microscopic
Scanning Electron Microscope (SEM) images were obtained on Cambridge S-360
SEM. The microscope has a resolution of 30 Å. It has a LaB6 source and an
acceleration voltage of 20kV. The stage features tilt capability from 0º to 90º.
The SEM images were also obtained on a Philips XL30 field-emission
environmental scanning electron microscope (ESEM). The microscope is equipped
with Everhart-Thornley secondary electron detector.
2.3. Spectroscopic
XPS analysis was performed using a Kratos Axis Ultra spectrometer.
Monochromatic AlKα X-ray excitation was used for the measurement of binding
energies of the metal catalysts on carbon paper. The base pressure was 9x10
-10
torr
and the operating pressure was 4x10
-9
torr. A hybrid (combination of magnetic and
13
electrostatic lenses) slot was used for analysis of a 0.7 x 0.3 mm
2
area of the sample.
The surveys of the samples were done with 160 eV as pass energy. High-resolution
scans (10) were collected with 40 eV as pass energy. Binding energies of all core
levels are referenced to the Carbon (as graphite) 1s core level (B.E. = 284.5 eV). The
curve fitting for the metal peaks was done on CasaXPS software using DS (Doniach
Sunjic) asymmetric line shapes.
2.4. Set up for thermal imaging
In the experimental set up (Figure 3) the fixed resistance is a flat rectangular surface
mount resistor of 100 ohm (6.4 mm x 3.2 mm in size, rating of 1 Watt). All the 96
resistors were mounted on the top surface of a two-layer printed circuit board. The
bottom of the board holds 96 platinum wires (0.25 mm in diameter, about 20 mm in
length) that are in series with the resistors on the top surface. The platinum wires
serve as counter electrodes for the electrochemical cells.
The carbon paper containing metal catalysts serves as the working electrode. Since
they are all on the same surface separated only by distance, they are shorted together.
The carbon paper was sandwiched between an aluminum plate on the bottom and a
Teflon block with 96 wells (both ends open) on the top. A silicone coated fiber
gasket (0.01mm in thickness, from LGS Technologies) was used between the carbon
paper and the Teflon block to seal the assembly.
14
De-ionized water was used for the electrolysis. Sodium perchlorate (NaClO
4
), from
Aldrich Chemical Co. was used as the electrolyte (pH = 5.05). Each cell was filled
with 0.75ml of this solution. The other salts, namely lithium perchlorate (LiClO
4
),
sodium nitrate (NaNO
3
), sodium tetrafloroborate (NaBF
4
) and lithium bromide
(NaBr) for screening of electrolytes were also purchased from the above Company.
An anti-reflective coating of Krylon ultra flat black paint (emissivity = 0.97, λ = 5
µm) helped reduce the reflected part of the thermal energy that comes from the
environment. The paint was used on all exposed surfaces in view of the camera. The
set up was placed in a black box that was made to enclose the entire space between
the lens of the camera and the bench on which the assembly lay.
2.5. Setup of IR Camera
The IR camera used for the study is a Merlin-uncooled microbolometer camera
provided by Indigo Systems. The camera consists of a Boeing Gen II uncooled Focal
Plane Array (FPA) incorporating a 320 X 240 matrix or a ‘staring’ array of
microbolometer detectors, sensitive in the long-wavelength infrared (LWIR) 7.0-14.0
micron range [Indigo Systems, 2000]. The Gen II FPA incorporates internal
resistance detectors that provide compensation for thermal drift and noise. The
camera supports both one- and two-point non-uniformity corrections. Non-
uniformity correction is used to compensate for the individual response of infrared
detectors. One-point correction is achieved by activating an internal flag source that
updates the offset correction coefficients to give a clear, uniform image. Using one
15
of the three Non-Uniformity Correction (NUC) tables provided by Indigo Systems a
two-point correction was attempted in the lab and finally performed at the factory.
Two-point correction updates gain and offset correction coefficients. NUC table 1
provided with the camera is utilized for temperatures ranges of 0 to 120ºC. This
camera is able to generate real time, 60Hz, 12-bit digital images. The FPA is
operated in the “integrate while read” mode, using a variable integration time from
10 µsec to 16 ms. It allows the user to choose from a corrected or non-corrected
image, where a corrected image is produced using a NUC table. The application of
the integration time occurs on a row-by-row basis, not on the entire FPA. As a result,
this camera is a rolling-mode device, whereas a photon detector camera is a
snapshot-mode device.
2.6. Measurement
Using a Keithley sourcemeter, the voltage was swept from 0-5V in steps of 2-3mV in
a stair configuration at the rate of about 50mV/s and the data was recorded. Although
the camera acquires 60 frames/sec the total number of frames acquired was limited
by the memory (< 1GB) on the computer. In general, this limitation required
skipping every few frames in the acquisition. This does not affect the measurements
since the voltage sweep rate is reasonably low. Talon GUI program was used for
acquisition of data in synchronization with the sourcemeter. A NUC 1-point
correction (internal calibration for camera) was done before every measurement
using the Merlin software for the IR camera. The default camera settings were used
with an integration time of 48µs.
16
2.7. Data analysis
The data was collected in a FITS (Flexible Image Transport System) file format. It
was then converted from hexadecimal FITS format to decimal TXT (ASCII) format.
Every 10-60 frames were averaged to reduce the noise and ease the analysis. At the
same time the 320 x 240 matrix was reduced in size to fit the image of just the
combinatorial array. The data was analyzed mostly in Origin7.0 program. The data is
plotted as an image of thermal counts in the given pixels. The color bar is arbitrarily
chosen to represent the change in thermal counts for example, from black-blue for
lower counts (cold) to red-white for higher counts (hot). A calibration of thermal
intensity results in the fact that about 100 thermal counts from the camera is
equivalent to a temperature rise of 0.1°C in the object in field-of-view of the camera.
3. Results and discussion
3.1. Preparation of catalyst library
The metal salt solutions were characterized as H
2
PtCl
6
solution of pH = 1.62, light
yellow in appearance, IrCl
3
solution of pH = 1.76, olive green and RuCl
3
solution of
pH = 1.57, brown in color. There was no spreading of the solution on the carbon
paper due to the surface tension of water.
17
The anodes of conductive metal oxides prepared by thermal decomposition of
chloride precursors onto carbon have been known to be highly dimensionally stable
electrodes.
21
The metal salts form the corresponding oxides on heating in air and the
oxides are further reduced to zero-valent metals using hydrogen gas. The catalyst
library was thus prepared by thermal decomposition. The calcination-reduction
process results in a smaller particle size and a narrow particle size distribution of the
metal particles.
MCl
3
.nH
2
O (or H
2
MCl
6
.nH
2
O) + O
2
 MO
x
+ Cl
2
(+ HCl + nH
2
O)
MO
x
+ xH
2
 M + xH
2
O
3.2. Characterization of metal catalysts
3.2.1. Microscopic
Observations on the optical microscope suggest that the metal particles are
distributed both on the surface of the fibers and in the interstices of the fibers of the
carbon paper. Scanning electron microscopy pictures led to more information on the
metal catalyst particles. The particle size is of the order of tens of nanometers. The
thermal reduction procedure in hydrogen gas is compared to the reduction in sodium
borohydride (NaBH
4
). In the second case, catalyst library was first calcined in air at
430°C for 4 hours and then reduced in aqueous NaBH
4
(200mM solution) for 10
minutes, followed by a rinse in DI water and dried in vacuum overnight (Figure 4,
Figure 5, Figure 6). The microscopic images show that when reduced in hydrogen
18
gas the carbon fibers seem more intact (Figure 7) and the particle size was over a
100nm smaller than the reduction by sodium borohydride.
The surface of iridium (Figure 8) appears as nanoparticles measuring about 30-40nm
in diameter. The surface of ruthenium (Figure 9) and of platinum (Figure 10) appears
as cracked-mud at low magnification but a closer inspection at high magnification
reveals that the catalysts consist of ultra-fine particles in the microscopically visible
cracks. The particle size for platinum and ruthenium measures to be about the same
(30-40nm) as that of iridium. Similar morphologies have been reported for platinum-
ruthenium catalyst on carbon or titanium
22
.
3.2.2. Spectroscopic
The XPS spectra were recorded on samples calcined and reduced but stored in
ambient conditions. The elapsed time between preparation and analysis was more
than a day. The main peaks observed in the survey scans of the different samples are
C 1s, Pt 4f, 4d and 4p, Ir 4f, 4d and 4p, Ru 3d and 3p and O 1s peaks (Figure 11).
The binding energies from the fitted spectra of Pt 4f, Ir 4f, and Ru 3d and 3p are
shown in Figure 12 and the peak positions with their FWHMs are listed in Table 1.
The binding energies of Pt 4f in the XPS spectra of platinum particles, supported on
carbon paper, are 71.4eV and 74.7eV with FWHM of 1.1eV. These values are
consistent with platinum in the zero-valent state.
23
The binding energies for the
platinum oxides are about 2eV higher than those of platinum metal.
24
The O 1s peak
19
at 532.0eV is symmetric and the atomic concentration of oxygen was the about the
same as of platinum. There could be some oxygen from the environment adsorbed on
the surface layer but the results are indicative of platinum metal in its pure state.
The experimental Ir 4f peaks are well fitted with binding energy positions at 62.0eV
and 65.0eV and a FWHM of 1.4eV. These values are about 1.0eV shifted from those
of iridium metal and the FWHM is little wider. The O 1s peak at 532.0eV is broad
with a shoulder and the atomic concentration of oxygen is about 2.8 times that of
iridium. The results suggest the presence of iridium oxide (IrO
2
) in the surface
layer.
25
The Ru 3d peaks were fit to binding energies of 280.8eV and 285.0eV with FWHM
of 1eV. These values are close to the value for ruthenium in the 4+ valence state.
26
The presence of ruthenium oxide in the surface layer is supported by the low energy,
broad and asymmetric peak of O 1s and the high atomic concentration of oxygen.
The Ru 3d
3/2
peaks near 285.0eV overlap with the aliphatic C 1s making it difficult to
make an accurate analysis. The Ru 3p
3/2
peak does not overlap another signal and
was used to analyze the oxidation state of the nanoparticles on the surface. The high
resolution Ru 3p
3/2
binding energy region is well fitted with the ruthenium in the 4+
oxidation state. The binding energy of Ru 3p
3/2
for bulk RuO
2
is generally in the
range of 462.4-463.2eV
23
. The atomic concentration of oxygen is slightly over two
times that of ruthenium. The results suggest the presence of ruthenium oxide (RuO
2
)
in the surface layer.
20
The spectrum analysis was also performed on Cl 2p core levels, along with the O 1s,
that are characteristic of the elements present under the conditions of preparation.
The results indicate that there is negligible amount (<0.1%) of chloride left from the
precursor salts.
The binding energies of platinum are close in value to the metal in its pure state
while those of iridium and ruthenium are closer in value to the metal oxides. Small
particle sizes and clustering of particles can cause a shift in the binding energies. The
presence of oxide in the surface layer could come from the formation of metal oxides
on exposure of metal surface to air.
3.3. Thermal imaging
3.3.1. Estimation of maximum possible error in heating of resistor
A modeling of temperature rise on the surface of resistor is given here, assuming the
absence of any convective cooling. The calculations are shown for a 100Ω resistor in
series with electrochemical cell where metal catalyst supported on carbon paper is
the working electrode.
Volume of the resistor = 6.4 x 3.2 x 0.6mm
3
Density of the resistor = 2.1g/cc (if it is graphite)
Thus, wt. of the resistor = volume x density = 25.8mg
21
Length of the experiment = 30sec
For the reference carbon paper:
Power dissipated across the resistor = P = i
2
R = (0.73)
2
x 100 = 53.3 x 10
-6
watt
Total heat supplied to the resistor = P.t = 53.3 x 10
-6
x 30 = 1.6 x = 10
-3
J
Specific heat to the resistor = J/g = 1.6 x 10
-3
/25.8 J/mg = 0.062 J/g
Specific heat capacity of graphite = 0.72 J/g-K
Thus, the temperature rise through the resistor = heat supplied/heat capacity =
0.062/0.72 = 0.086K (< 0.1K)
For metal catalyst supported on carbon paper:
For a Ru catalyst supported on carbon paper, current, i = 1.7mA
Thus, temperature rise through the resistor = 0.46 K
The above calculations give a rough idea of the upper bound on temperature
difference as about 0.3K in the heating between cell with a metal catalyst and cell
with the reference carbon paper. Thus the IR camera, with a resolution limit of 0.1K,
should be able to distinguish a good catalyst in reference to the supporting carbon
paper, although it may be close to the limit for distinction between two catalysts.
22
3.3.2. Optimization of system parameters
The process of development of a combinatorial screening technique involved
configuration and optimization of various parameters. It involved both hardware and
software challenges. Some of the hardware problems that I addressed in the process
and some of the parameters that I optimized are as follows:
(i) The basic design of the set up, from a stable and workable layout of the
array on the bench to the proper positioning of the IR camera.
(ii) Reflection: The construction of a black box and the use of a black
absorptive paint towards reduction of reflections from surface in the field
of view of the IR camera (Figure 13).
(iii) Value of the resistor on the board: The construction of a circuit with a
range of resistor values (100Ω, 270Ω and 1000Ω) to image the difference
in power loss across each of the resistors in response to varying currents
through the resistor (Figure 14). As the value of resistor increases the
thermal intensity becomes more distinct for the same amount of current
flowing through the circuit, which is expected. But the high value of
resistor gets too large to distinctly observe the catalytic activity in the
cells. This is also understood by the fact that since there is no reference
electrode in the cell a higher value resistor would mean that the voltage at
the counter electrode would vary a lot with the current.
(iv) Calibration: The external calibration of the IR camera. This led to the
reduction of some bad pixels (Figure 15) on the CCD of the camera.
23
(v) Gasket: The choice of gasket, its optimal thickness and material (silicone-
reinforced rubber/ silicone coated fiber) to avoid any leakage of
electrolyte from one cell to another. The use of thin silicone coated fiber
sheets showed no leakage of electrolyte from one cell to another.
(vi) Support: The choice of material for the supporting plate (aluminium/
copper/ stainless steel) used to hold the carbon paper. Copper gets etched
easily and so does aluminum. Stainless steel seems less uniform than
aluminum since it is too rigid to conform to the surface of carbon paper.
We settled for aluminum with occasional re-surfacing of the plate.
(vii) Carbon paper: The thickness (0.37mm for TGP-H-120/0.28mm for TGP-
H-090/0.19mm for TGP-H-060), dimensions (for the array) and the
surface finish (Teflon-coated or not) of carbon paper used as the electrode
substrate. The thicker the paper, the harder it was to sandwich between
the layers. The aqueous solution of metal salt was hard to deposit on the
Teflon-coated carbon paper.
(viii) Metal salts: The choice of precursor salts (hydrogen/ sodium/ potassium
salts) and the optimal solution concentration to get finely dispersed
particles. Sodium and potassium salt were harder to reduce to the zero-
valent transition metal without any contamination from the main group
metals.
(ix) Nature and concentration of electrolyte: Early on in the study, we looked
at a few electrolytes for the nature and optimum concentration of the
electrolyte towards the oxidation of water. The concentration of
24
electrolyte was varied from 40mM to 120mM in steps of 20mM for
sodium perchlorate(NaClO
4
), lithium perchlorate(LiClO
4
), sodium
nitrate(NaNO
3
), sodium tetrafloroborate(NaBF
4
) and lithium
bromide(NaBr). Platinum and palladium particles were prepared as
catalysts for the experiment. The voltage was swept from 0-5V at a rate
of about 45mV/s. The thermal images (Figure 16) indicate that the most
active cells have Pt and Pd as catalyst with electrolyte concentration of
0.04-0.08M of sodium perchlorate or lithium perchlorate. This
experiment suggests that the tetrafloroborate, bromide and nitrate salts are
not very active electrolytes for the oxidation of water on Pt or Pd metal
catalysts. In the following experiments sodium perchlorate was used as
the electrolyte.
The above optimizations lead to the choice of parameters and the setup used in the
experiments described here. There are many different experiments that were
performed during the process of this study using different combinations of the metals
as catalysts. Only a few examples highlighting the main results are given here.
3.3.3. Individual measurements
A library of metal nanoparticles containing ruthenium, iridium and platinum was
prepared and placed in the combinatorial setup. A silver-silver chloride (Ag/AgCl)
microelectrode was used as the reference electrode and a single platinum wire of the
25
same dimension as in the combinatorial measurement was used as the counter
electrode. The counter and reference electrodes were moved from cell-to-cell for
measurement in current variation across the working electrode. A linear sweep
voltammogram of the different catalysts measured from 0-2V (vs. Ag/AgCl) at a
scan rate of 100mV/s is shown in Figure 17. There is a significant amount of current
through the cells at an applied potential of about 1.1V. The results suggest that for a
significant current density through the cell, ruthenium has the lowest overpotential
towards the reaction. Thus we can say that ruthenium is the most active metal
catalyst in the given conditions towards the oxidation of water although not the most
stable. Iridium metal seems active and stable in the charge transfer or activation
controlled region of the process. The results from this experiment serve as a useful
quantitative reference to the combinatorial measurements that are qualitative in
nature. A rough calculation was done by measurement of the potential drop across
the fixed resistor at a given applied potential to estimate the amount of current
flowing through the cell. This current is of the order of 2mA at an applied potential
of 4V that translates to a potential of about 1.9V versus the Ag/AgCl reference
electrode (The thermodynamic potential for the above reaction at a pH of 5.05 at
25°C is a 0.73V vs. Ag/AgCl electrode.). Thus the potential at which the difference
in thermal activity of any two catalysts becomes evident is close to 2V vs. Ag/AgCl.
It suggests that overpotential of at least 1V is required to observe by infrared
imaging a difference in thermal activity of metal catalysts for the oxidation of water.
26
3.3.4. Combinatorial measurements - Carbon paper as working electrode
A thermal imaging experiment was performed on the carbon paper (as received).
This serves as a reference to determine the uniformity in activity across the 96-cell
array. In this experiment, carbon paper is the working electrode, platinum wire is the
counter electrode and a 0.1M solution of sodium perchlorate is the electrolyte. The
potential was applied from 0-6V at a rate of about 53mV/s.
There was no observed leakage of electrolyte from one cell to another. Some cells
close to the center appear to be more intense than the others on the array [Figure 18
(a)-(d)]. The difference in the thermal counts from a hot spot to a cold spot is about
100-200 counts that accounts to about 0.1-0.2°C in temperature difference. If the
thermal intensity is analyzed for a cell that is away from the intense region, it
appears more uniform across the rows and columns [Figure 18 (d) vs.(c)]. This
difference in intensity was first attributed to reflection from the surroundings or from
the metallic endings of the resistors on the surface board. Following this, a 2-point
correction on the camera was performed and then Krylon flat black paint was spray
coated on the surface to take care of any reflection from the surface in the focal plane
array of IR camera. The results from the modified setup are somewhat better (Figure
19). There is no obvious region of higher intensity due to reflection from the surface,
even at about 4.7V where the resistors become distinct from the background. The
origin of this reflection seems to be the camera itself. The high intensity area shifts
as the tilt of the camera was changed to different angles, although changing the
camera tilt results in a non-uniform collection of thermal counts. Assuming that all
27
other parameters are consistent from one cell to another, this non-uniformity is
attributed partly to the reflection of the camera lens onto the object in view. An
example of this reflection on a steel plate at room temperature is shown in Figure 13.
It decreases with an absorptive coating on the surface in view of the camera. It is
hard to judge the precise activity in the different cells given the non-uniformity
across the field of view of the camera.
3.3.5. Combinatorial measurements - Metal particles as working electrode
A library of platinum and iridium metal particles was prepared by arranging them in
alternate diagonals. The choice of the above two metals was based on the difference
in their activity such that it would be easy to distinguish them apart. The voltage was
swept from 3-6V at a rate of about 35mV/s. The evidence of activity in the thermal
images is seen between 4V and 4.5V (Figure 20). In general, the cells containing
iridium metal as catalyst appear hotter than the ones with platinum metal at applied
potentials between 4.5V and 6V. The difference in the activity of the two metal
catalysts is about 50-100 thermal counts. This is equivalent to less than 0.1 degrees
change in temperature on the surface being imaged. It is near the resolution limit
(0.1°C) of the IR camera. This being the case for individual metals, it would be very
difficult to tell the difference in activity between a mixture of catalysts with different
concentrations, like a 50/50 Pt/Ru and a 60/40 Pt/Ru, where the difference is even
smaller. Many such libraries of different combinations of metal catalysts were
screened but in all measurements the above limitation is reached in the distinction of
28
activity using thermal output. Thus, we conclude that it is hard to draw conclusions
on the activity of metal catalysts in lowering the overpotential for oxidation of water
using thermal output as a method of screening.
Quantitative analysis using Matlab: The data from the qualitative thermal images
was studied in a more quantitative way using Matlab (Appendix A). The Pt-Ir
combinatorial library, mentioned above was analyzed to obtain the average thermal
counts through the experiment. The rough geometric position of the center of
resistors is determined by picking the three corners of the array on any one of the
frames and calculating the position of remaining resistors from there. The intensity
of thermal counts is averaged for nine pixels around the center of each resistor. The
sum of thermal counts and the average and standard deviation of the thermal counts
is plotted against the number of frames (Figure 21). The number of frames captured
by the IR camera is a direct function of time and of the applied voltage. The results
indicate that although there is inhomogenous across the array, overall the iridium
catalyst is more active than the platinum catalyst at any applied potential. The
difference in the activity of the two metal catalysts towards the oxidation of water
becomes evident at around 4V (about 20 frames in the graph). The difference in the
averaged intensity of thermal counts for the two catalysts seems to be less than 50
counts. The quantitative analysis helps quantify and support the qualitative results
obtained by thermal output of combinatorial screening.
29
4. Summary
Thermal output of current through the cells is used as a method for combinatorial
screening of metal catalysts towards the oxidation of water. An infrared camera
images the joule heating across a fixed resistor in series with the cell and the thermal
intensity is analyzed as a measure of the activity of metal catalysts at the electrode.
The larger the current through the cell at some applied potential, larger is the amount
of heat dissipated at the resistor, higher the thermal intensity for the cell and thus
greater the activity of catalyst at the electrode in the cell. The metal catalysts,
supported on carbon paper, were prepared by thermal reduction of their precursor
salt solutions. The surface characteristics of the resulting metal particles were studied
using microscopy and spectroscopy. The metal particles are of the order of about
50nm in diameter with a fairly uniform distribution. Spectroscopic data indicates
zero-valent form of metals while the higher oxidation states cannot be ruled out due
to measurements in ambient conditions.
The setup of combinatorial array allows screening of metal catalysts in 96
electrochemical cells at one time. The screening of different electrolytes results in
optimizing the nature and concentration of electrolyte for further experiments. From
one of the experiments, using platinum or palladium electrodes, we found that a
0.1M solution of sodium perchlorate would be optimal for use as electrolyte. The
screening method is used for a comparative study of the catalytic activity of metal
particles of iridium, platinum and ruthenium towards the oxidation of water. In one
30
of the experiments described here, most of the cells containing Ir-particles at the
electrode seem to be higher in thermal intensity than the ones with Pt-particles,
although the distinction is not uniform throughout the array. The order of catalytic
activity at an applied potential of about 4.5V is ranked as Ir > Pt in reference to the
supporting carbon paper. In order to distinguish between the thermal intensity of
cells containing metal particles at the electrode using thermal output method, a large
amount of current has to flow through the cell. This equates to a kinetic region where
large amounts of oxygen gas is produced by oxidation of water at the electrode. We
are interested in the region where the current density starts to increase from being
negligible to a significant amount but not too large (we define the potential at about
this current as the turn-on potential). Roughly speaking this current would be a few
hundred or less microamperes in magnitude. Some of the limitations of the thermal
output method of combinatorial screening seem to be the cooling of resistors by
convection, a time delay in heating of the resistors and being near the resolution limit
of infrared camera. In an attempt to amplify the magnitude of current at the turn-on
potential we developed another method of screening that is based on a visual output
approach. It is discussed in Chapter 2 of this document.
31
Chem. Mater. 14 (2002), 3343
Figure 1 Current-voltage curves from screening of nanoparticles of platinum group
metals supported on carbon paper. Results from individual metals are shown on top
and from combinations of metals are shown on the bottom. The scan rate is 5mV/s.
32
Figure 2 Toray carbon paper, the surface as seen on SEM and the cross-section of the
fibers
33
Figure 3 Combinatorial setup for infrared thermal imaging of 96 electrochemical
cells used for the screening of metal catalysts towards the oxidation of water. The
bottom picture shows the working electrode (carbon paper supported metal particles)
sandwiched between an aluminum plate and Teflon block with 96 wells.
34
(i) (ii)
Figure 4 Scanning electron microscope pictures of Pt metal catalyst, on the surface
of a carbon fiber, prepared by thermal oxidation in air followed by reduction in (i)
hydrogen, and (ii) NaBH
4
.
(i) (ii)
Figure 5 Scanning electron microscope pictures of Ir metal catalyst, on the surface of
a carbon fiber, prepared by thermal oxidation in air followed by reduction in (i)
hydrogen, and (ii) NaBH
4
.
35
(i) (ii)
Figure 6 Scanning electron microscope pictures of Ru metal catalyst, on the surface
of a carbon fiber, prepared by thermal oxidation in air followed by reduction in (i)
hydrogen, and (ii) NaBH
4
.
Figure 7 Scanning electron microscope pictures of carbon fibers imaged after
thermal oxidation in air followed by reduction in hydrogen.
36
Figure 8 SEM pictures of iridium catalyst supported on carbon paper.
c
a b
d
37
Figure 9 SEM pictures of ruthenium catalyst supported on carbon paper.
c
e
a
d
f
b
38
Figure 10 SEM pictures of platinum catalyst supported on carbon paper.
c
a b
d
39
0
20000
40000
60000
80000
100000
120000
0 100 200 300 400 500 600 700 800
binding energy (eV)
intensity (cps)
0
20000
40000
60000
80000
100000
120000
140000
0 100 200 300 400 500 600 700 800
binding energy (eV)
intensity (cps)
Figure 11: Continued
5p
4f
7/2
4f
5/2
4d
5/2
4d
3/2
4p
3/2
C 1s
(a)
(b)
40
0
20000
40000
60000
80000
100000
120000
140000
0 100 200 300 400 500 600 700 800
binding energy (eV)
intensity (cps)
Figure 11 XPS survey scans of (a) Pt, (b) Ir and (c) Ru nanoparticles on the surface
of carbon paper.
4f
7/2
4f
5/2
C 1s + Ru 3d
3p
1/2
(c)
41
Figure 12: Continued
a.
b.
42
Figure 12 XPS spectra of the metal (Pt, Ir and Ru) nanoparticles on the surface of
carbon paper. (a) Pt 4f, (b) Ir 4f and (c) Ru 3d and (d) Ru 3p core levels.
c.
d.
43
(a)
(b)
Figure 13 Thermal image shows reflection from (a) aluminum plate and from (b)
metallic ends of the fixed resistors on the array that are in the field of view of the
camera.
44
Figure 14 A thermal imaging experiment for optimization of the magnitude of fixed
resistor in series with the electrochemical cell. Different values of resistors were used
in parallel with each other and in series with a variable resistor to adjust the amount
of current flowing through the circuit. Rows: row 1 is 1000Ω resistors, row 2 is
270Ω resistors and row 3 is 100Ω resistors. Columns: column 1 is 7mA current,
column 2 is 6mA current, column 3 is 5mA current and column 4 is 4mA current
through the circuit.
45
Figure 15 Thermal image that highlights the number of bad pixels in the infrared
camera that was used for thermal output of combinatorial screening of catalysts
towards the oxidation of water.
46
Sodium perchlorate
Sodium nitrate
Lithium perchlorate
Sodium tetrafloroborate
Lithium bromide
Figure 16 Thermal imaging of a library of Pt and Pd particles with different
electrolytes in varying concentrations. The scan was from 0-5V at about 45mV/s.
The image shown here is at an applied potential of about 5V. The color bar on the
right gives the thermal counts (a 100 thermal counts is equivalent to about 0.1°C rise
in temperature).
Pd Pd Pd Pd Pd Pd Pt Pt Pt Pt Pt Pt
Pd Pd Pd Pd Pd Pd Pt Pt Pt Pt Pt Pt
Pd Pd Pd Pd Pd Pd Pt Pt Pt Pt Pt Pt
Pd Pd Pd Pd Pd Pd Pt Pt Pt Pt Pt Pt
Pd Pd Pd Pd Pd Pd Pt Pt Pt Pt Pt Pt
Pd Pd Pd Pd Pd Pd Pt Pt Pt Pt Pt Pt
Pd Pd Pd Pd Pd Pd Pt Pt Pt Pt Pt Pt
Pd Pd Pd Pd Pd Pd Pt Pt Pt Pt Pt Pt
none
0.04M
0.06M
0.08M
0.10M
0.12M
0.12M
0.10M
0.08M
0.06M
0.04M
none
47
Figure 17 Linear sweep voltammograms of the different metal catalysts as the
working electrodes of the cell obtained on individual measurements in the
combinatorial setup. The current-voltage curves from cells with metal catalysts are
referenced to that obtained from supporting carbon paper. The scan rate was 100
mV/s.
48
(a)
(b)
Figure 18: Continued
49
(c)
(d)
Figure 18 Thermographs from a blank carbon paper library obtained on a scan from
0-6V at a rate of 53.5mV/s. A 100Ω array (uncoated) of resistors was used for
50
imaging the thermal output of this experiment. The images are shown at about
(a)1.0V, (b)2.0 V and (c), (d)5.3 V. The thermal intensity in image (d) seems more
uniform across the array in the region where there is no obvious reflection, in
comparison to that in image (c) where there is reflection. The color bar on the right
gives the thermal counts (a 100 thermal counts is equivalent to about 0.1°C rise in
temperature).
51
(a)
(b)
Figure 19: Continued
52
(c)
Figure 19 Thermal images of a combinatorial library of the blank carbon paper
scanned from 3-6V at a rate of about 35mV/s. A circuit board with 270Ω resistors
was used here. Black paint was sprayed on it to minimize reflection from the surface.
The images are shown at applied potentials of (a) about 5.8V, (b) 5.5V and (c) 4.7V.
The color bar on the right gives the thermal counts (a 100 thermal counts is
equivalent to about 0.1°C rise in temperature).
53
(a)
(b)
Figure 20: Continued
54
(c)
Ir Pt Ir Pt Ir Pt Ir Pt Ir Pt Ir Pt
Pt Ir Pt Ir Pt Ir Pt Ir Pt Ir Pt Ir
Ir Pt Ir Pt Ir Pt Ir Pt Ir Pt Ir Pt
Pt Ir Pt Ir Pt Ir Pt Ir Pt Ir Pt Ir
Ir Pt Ir Pt Ir Pt Ir Pt Ir Pt Ir Pt
Pt Ir Pt Ir Pt Ir Pt Ir Pt Ir Pt Ir
Ir Pt Ir Pt Ir Pt Ir Pt Ir Pt Ir Pt
Pt Ir Pt Ir Pt Ir Pt Ir Pt Ir Pt Ir
Figure 20 Thermograph of an array containing platinum and iridium metal catalysts
as working electrodes in a series of alternating diagonals. A dashed line indicates the
cells containing iridium particles. The thermal counts for the pixels on this line are
55
indicated in the x-z(top) and y-z(right) graphs. The thermal images shown here are at
applied potentials of (a) 4.5V, (b) 5V and (c) about 5.8V.
Figure 21 Quantitative analysis of the thermal counts using thermal images from a
combinatorial library containing iridium and platinum catalysts for the oxidation of
water.
56
Table 1 Binding energy (BE) and full width at half maximum (FWHM) of the core
levels measured by XPS of the catalyst metal particles supported on carbon paper.
Region BE (eV) FWHM (eV)
Pt 4f
7/2
71.4 1.1
Pt 4f
5/2
74.7 1.1
Ir 4f
7/2
62.0 1.4
Ir 4f
5/2
65.0 1.4
Ru 3d
5/2
280.8 0.9
Ru 3d
3/2
285.0 1.0
Ru 3p3/2
Ru 3p1/2
462.8
484.8
4.2
3.9
Values are determined relative to the C 1s BE at 284.5 eV.
57
Chapter 1 References
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2. Yudin A. K., Siu T., Curr. Opin. Chem. Bio., 5 (2001), 269.
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58
20. Wenzel, D., Bernal, A., Burris, D., and Dalton, A.M., Thermal Energy Emission Diagnostics Enhancement to the Advanced Power Supply
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59
Chapter 2: Combinatorial screening of metal catalysts for
oxidation of water using visual output
1. Introduction
A general introduction to combinatorial screening of metal catalysts for oxidation of
water is given in chapter 1 of this document. The preparation and surface
characterization of metal particles and the setup of electrochemical cells in a
combinatorial array for screening of metal catalysts are also described in that
chapter. The combinatorial screening method using visual output stems from the
results and limitations of thermal output method discussed in the last chapter.
The thermal imaging method of screening was used as an indirect method to screen
metal catalysts in a parallel combinatorial fashion. The results show that the thermal
output method works as a qualitative preliminary screening of metal catalysts if the
difference in their turn-on potentials is large enough at a significantly large amount
of current through the cell. This method has some limitations from the use of
resistors, like cooling by convection and a time delay in their heating. One of the
bigger limitations to its use is its insensitivity to small amounts of current through
the cell due to the resolution limit of infrared camera. The data obtained from
individual measurements suggests that the slope of current-voltage curves changes
significantly (i.e. significant kinetic activity) at a few tens of microamperes of
60
current through the cell. Thus, we would like to compare the overpotential of
different metals for the reaction at a few tens of microamperes of current through the
cell. In order to do so, we need to somehow amplify the current in our output such
that a very clear distinction is observed in the activity of metal catalysts. This is
achieved by building what we call a ‘sensitive digital ammeter’.
A direct measurement of current at each electrode in an array that can be
independently addressed can provide fast monitoring of reactions without the need
for any kind of indicator. Electrochemical screening methods are direct
measurements in the sense that the current and potential of each individual catalyst is
accurately controlled and monitored.
1
The electrochemical cell can be constructed
such that either the moveable counter and reference electrodes are sequentially
brought in contact with individual working electrodes
2,3
or the fixed counter and
reference electrodes are in contact with all of the working electrodes in the same
electrolyte
4,5,6
.
The first approach of serial measurement was used to study the effects of catalyst
loading and methanol concentration on the performance of methanol | air cells and to
screen the activity of various metal-doped tungsten oxides for hydrogen production
by photoelectrolysis of water. It was using this technique that Warren
6
had shown
Pt/Ru (50/50) as the most active catalyst for methanol oxidation by electrodepositing
Pt-Ru on an array of Pt electrodes. Gorer
7
studied electrodeposited ternary methanol
oxidation catalysts in multi-electrode arrays. The ease of serial measurement has
61
been improved by the development of automated systems (Figure 22) for high-
throughput photoelectrochemical screening of activity of supported Au clusters for
water oxidation and CO oxidation.
8
This approach is economical with the use of just
one potentiostat and a current follower but practically slow since the electrodes need
to be physically moved.
The second approach of parallel measurement was demonstrated in the screening of
active zones from a 64-electrode array of gold surfaces modified with organosulfur
monolayers of different chain lengths. The direct measurement improved to a
pseudoparallel screening method with the use of special ASIC (application-specific
integrated circuit) switches to apply potential to all the working electrodes of the
library via bias lines and read the current in series from individual working
electrodes
9
. The multiplexing (in the ms range) and serial read-out (pA currents) of
electrode arrays was demonstrated by redox recycling of p-aminophenol in an
interdigitated microelectrode array made in silicon technology at potentials that are
addressed by the ASIC to the anodes and cathodes. This approach is slow and suffers
from the contact of all electrodes, active or non-active, with the solution at all times.
The pseudoparallel screening approach was also used to study the oxidation of
adsorbed carbon monoxide and methanol in solution and the reduction of oxygen on
a series of carbon-supported platinum catalysts of varying particle sizes.
10
They
constructed a cell consisting of 64-element array of electrodes that are at the same
potential in a common electrolyte addressed by a single channel potentiostat and a
62
multi-channel current follower (Figure 23). The electrode currents were collected
serially and thus limited by the speed of computation. Larger particle sizes were
found to be more active for the oxidation of methanol and reduction of oxygen in
H
2
SO
4
electrolyte at room temperature. The difference in activity of metal particles
with varying sizes is much smaller than the difference in activity of metal-based
alloy catalysts for the same reaction. This method has also been used to study the
spatial pattern forming at corroding electrodes
11,12
and for the screening of positive
electrode candidates for lithium batteries
13
. A single voltage follower and 25 current
followers were used to simultaneously obtain polarization curves from the 25
catalytic spots on array for the ranking of four different catalysts, one made by
sodium borohydride reduction and the rest were commercially available direct
methanol fuel cell anode catalysts.
14,15
It is difficult to compare the above methods or draw a conclusion since they differ in
the method of preparation of catalyst, the choice of catalyst used and the chemical
reaction in consideration. The two approaches that we have taken, electrochemical
screening by thermal output and by visual output, are towards the analysis of metal
catalyst for the oxidation of water. They both involve the use of a consistent method
for preparation of metal catalysts and use the same combinatorial setup for the cells.
The difference lies in the output as a way to measure current through the cells. A
truly parallel cyclic voltammetric screening method requires the simultaneous
control of potential and measurement of current at a large number of electrodes (64
to 96 in number). This multiplexing function is not readily available as commercial
63
instrumentation. Thereby research groups have developed alternate methods, parallel
and serial, to screen electrocatalysts. Described here is an alternate parallel screening
method that we developed in the laboratory for screening of catalysts towards the
oxidation of water.
A sensitive digital ammeter makes use of an operational amplifier as a comparator
for voltage and a LED (light-emitting diode) for measurement of current through the
cell. The potential difference across a fixed resistor in series with the electrochemical
cell is compared against a known voltage and the output is used to illuminate the
LED. The potential at which the LED illuminates is defined as the turn-on voltage at
a known current through the electrochemical cell. The turn-on voltage defined here
relates to the overpotential (energy required in addition to the thermodynamic
potential) required for significant kinetic activity at the electrode where the reaction
is studied. The lower the turn-on voltage at a known current through the cell, the
more active the catalyst is towards reaction at the electrode.
The advantage with this technique is that it is comparable to direct measurement of
current through electrochemical cells in parallel. The electronic circuit is built from
components that are economically available that makes it a low cost technique for
screening large numbers of catalysts for a reaction. There is no limit to the nature
and concentration of electrolyte for different cells in a single setup of combinatorial
array. It is a fast and simple approach to qualitative combinatorial screening of metal
catalysts prior to individual quantitative measurements.
64
The initial experiments were performed using a two-electrode system in the
electrochemical cell. This is referred to as version 1 of the screening method. There
is no reference electrode used in this version, so the turn-on voltage cannot be
referenced directly to a standard potential. A better design of the electronic circuit
reduced the amount of estimated error in electrical measurement of current through
the cells. This is referred to as version 2 of the screening method, where a
potentiostat was built and introduced in the electronic circuit that allows the use of a
reference electrode in each cell. The results from screening of metal catalysts using
this method are direct and consistent. The two methods are described in details in the
following section.
2. Experimental section
2.1 Description of the screening method
Version 1
The basic working principle for the ammeter electronic circuit in the screening
method is as follows (Figure 24). The positive input voltage (V+) to the operational
amplifier is the voltage drop across a fixed resistor (22Ω in our experiment), in series
with the counter electrode of the cell. An ac waveform generator drives the negative
input voltage (V-) to the amplifier. The difference in the two input voltages results in
a voltage drop that corresponds to positive (V++) or negative (V--) driving voltage
65
for the operational amplifier, as shown in Figure 25. The driving voltage of
operational amplifier is labeled as V
0
(not shown in the figure). When V+ is greater
than V-, the LED lights up. The most active metal catalyst draws the most current in
the electrochemical cell at any given potential. This amounts to a greater potential
drop across the fixed resistor of 22Ω. Thus, the LED for this cell turns on first. The
order in which the LEDs light up is a direct measure of the catalytic activity of metal
particles in the electrochemical cells. The sequence is observed by the naked eye
and/or recorded for analysis using a digital video camera (30 frames/second).
For preliminary experiments, the electronics was assembled for 16 cells (4x4 array)
on a printed circuit board. Platinum wires (as counter electrodes for the reaction)
were soldered to the bottom face of the electronic board. The red LEDs were surface
mounted on the top face of the board (Figure 26c). The schematic shown in Figure
24 shows a layout of the ammeter circuit for one electrochemical cell. The electronic
board supports one ammeter circuit per electrochemical cell.
The working electrode of cell with the metal catalyst supported on carbon paper
forms the anode (+) and the counter electrode (platinum wire) is the cathode (-),
grounded for convenience in this set up. The combinatorial wells of the Teflon block
(Figure 26a) hold the electrolyte solution. A sourcemeter is used to sweep voltage, in
parallel, across the electrochemical cells. The input voltage to the operational
amplifier is a triangular waveform (frequency = 1 kHz) (Figure 26b). The frequency
of this waveform is such that the LED appears to be illuminated once it is turned on.
66
The brightness of LED increases as the cell draws more current with increasing
voltage of the sweep. A current-limiting resistor of 500Ω placed in series with the
red LED limits the current through the output circuit.
Version 2
The second version of combinatorial screening method uses a similar ammeter
circuit (Figure 27) but with a potentiostat added to each electrochemical cell such
that the measurements become more direct with the use of a reference electrode in
the improved circuit. The visual output of turn-on potential, as a measure of the
catalytic activity, is the same as in version 1 of the screening method.
For a preliminary study of the method, an 8x2 array was assembled as a stack of
three electronic boards. This cumbersome approach is needed because of the very
fine pitch of cells. The top board has LEDs for imaging, the middle board has
potentiostats and the bottom board holds the electrodes, both counter and reference
electrodes (Figure 28, Figure 29). The voltage scan (voltage form, range and sweep
rate) at the potentiostat is controlled by Keithley sourcemeter.
The op-amp AD8625 works like a potentiostat that measures the current. Since it has
ultra high input impedance, negligible current flows through it. It has a high gain,
negative feedback configuration. The larger the potential drop at the counter
electrode (CE), the larger the drop at the reference electrode (RE). It maintains the
reference electrode at the same potential as the control voltage. No current flows
67
through the reference electrode. A silver-silver chloride wire is used as the reference
electrode. The reference and counter electrodes for each cell are cased in a plastic
tube such that it is easy to align and lower the electrodes into the combinatorial
wells, without bending the thin electrode wires. The working electrode (WE),
catalyst-modified carbon paper, is ground in electrical terms, for convenience. The
counter electrode, platinum wire, is at whatever potential it needs to be, some voltage
higher than the reference electrode. As it is in a potentiostat, current i
CE
= i
WE
.
We chose the value of current-measuring resistor R to be 1000Ω. The op-amp,
AD620 is a low cost, high accuracy instrumentation amplifier; together with the
resistor R it makes an ammeter. It is used as a buffer that makes the potential drop
(of say 1V, from 1mA current flowing through 1kΩ resistor) appear on the output
relative to this input. The op-amp, LM324A on the top board functions as a
comparator for the display unit. Two sets of LEDs are used for imaging on the top
board. The current to red LEDs (Hi-monitor on the board) is tuned to the potential
drop set on the output of ammeter. The green LEDs (Low-monitor on the board) are
set to a choice of some percent value of the above potential drop, for example, at half
the potential of the red LEDs. In this case, the LEDs turn off, rather than turn on,
with the voltage sweep. The potential at which the LEDs turn off is a direct measure
of the turn-on potential of the cell and thus the electrochemical activity of the
catalyst.
68
2.2 Materials and Equipment
The materials used for setup of combinatorial screening are given in Chapter 1. The
components used in addition to those mentioned earlier are listed here.
Version 1
Express PCB was used to make the printed circuit board (the prototype board) for an
array of 12x8 (96) individual electronic circuits. The electronic components
purchased from Digi-key Corporation include the red LEDs (surface mount),
capacitors (0.15µF) and resistors (22Ω and 500Ω). The operational amplifiers
MAX437CSA (low-noise, high precision, offset voltage: 15 µV max) were obtained
from Maxim Integrated Products. Platinum wire (0.25 mm in diameter), sodium
perchlorate and tetramethylammonium bromide was purchased from Aldrich
Chemical Co. and used as received. Platinum wire was cut into strips of 20 mm in
length. Keithley 2400 sourcemeter was used to control the potential sweep across the
electrochemical cells. Hewlett Packard 3466A digital multimeter was used to
generate the triangular ac waveform. DC power supplies from Hewlett-Packard were
used as sources for all other circuits. Digital video camera recorder from Sony (2.11
Mega Pixel, 30 frames/sec) was used to record the sequence in which LEDs turn on.
Version 2
The material and equipment listed above was also used for the second version of the
method. In addition, the op-amps used here include AD620 (input offset voltage: 185
µV max, output offset voltage: 2mV max, input offset current: 2.0nA max), AD8625
(input offset voltage: 0.5mV max, input offset current: 1.0pA max) and LM324A
69
(input offset voltage: 3.0mV max, input offset current: 30nA max) from Analog
Devices. The red and green LEDs (surface mount, 0805) were purchased from Digi-
key Corporation. Sodium chloride was purchased from Aldrich Chemical Co. The
silver wire (Premion, 99.9985%, 0.25mm diameter) was obtained from Alfa Aesar. It
was cut into strips 20 mm long, washed with ethanol and oxidized in ambient
conditions for 20 minutes in a Clorox bleach solution to form the silver chloride salt
on the silver wire. The silver-silver chloride wires were used after rinsing them with
DI water. They were stored in saturated potassium chloride solution, washed and
rinsed with DI water before each use. A polycarbonate plastic pipe was cut into
dimensions and glued onto the bottom board for casing the platinum and silver wires.
2.3 Error estimates
The thermodynamic potential for oxidation of water is 1.229V vs. NHE. With
conventional electrodes there is an overpotential required to overcome the energy
barrier for significant current density at the electrode. With the use of platinum group
metals as catalysts, typical overpotential is in the range of 0.5-1.0V. We are
interested in measuring the applied potential at a current where the rate of reaction
becomes significant. We define this as the turn-on potential for activity of the
catalyst for the reaction. To estimate this current value, current-voltage curves were
recorded using a standard potentiostat on individual electrochemical cells of the
combinatorial setup (Figure 30). The measurements were done using a standard
silver-silver chloride reference electrode and a platinum wire as counter electrode.
70
Error from the working electrode
From the above measurements a rough estimate is made for the value where current
starts to increase at a significant rate and this is determined to be about 30µA of
current. At this current value, the measurements give a spread of about 20-50mV in
the applied potential at working electrode. The spread in applied potential is larger at
higher current densities as the overpotential increases. Thus the error in measurement
of turn-on potential at the working electrode is of the order of 50mV. It implies that
the preparation of metal catalyst supported on carbon paper as the working electrode
results in some non-uniformity across the array. In order to discriminate between the
turn-on potential of metal catalysts at the above current value, a minimum error of
50mV could occur from the working electrode.
Error from the electronics in combinatorial measurement (version 1)
In the set up for version 1 the value of current where the turn-on potentials for
catalysts could be compared is determined to be about 500µA. This value is much
higher than 30µA used in version 2. Given the circuit, LEDs for the cells with blank
reference at working electrode require a minimum offset voltage of 10-15mV in
order to turn on before the end of experiment (voltage sweep). The above voltage
drop across a 22Ω resistor translates to a minimum current value of about 450µA.
The possible sources of error from the electrical circuit used in measurement of turn-
on potential, at a current of 450 µA through the cell, are listed here.
71
1. Current-measuring resistor, R
L
= 22Ω (1% tolerance).
Voltage drop across resistor at the current where LEDs turn on = (450µA) x (22Ω) =
9.9mV. With 1% tolerance of the 22Ω resistor, the maximum error in current
measurement is 4.5µA. Calculations from individual I-V curves of different catalysts
(Figure 30) show that the maximum error in the measurement of turn-on potential
from this resistor is about 1.3mV.
Calculation of the above error (an example):
(∆V/∆I)
at 30µA
V/µA x 4.5µA = (1.264-1.263)/(450.5-447.0) V/µA x 4.5µA
= 1.28mV
2. Op-amp, MAX437CSA.
The maximum offset voltage of the op-amp = 15µV. For a 9.9mV potential drop, this
translates to a maximum possible error of 0.15% in voltage. It is very low and can be
considered a negligible source of error in measurement of turn-on potential.
3. Printed circuit board.
The return current from the LEDs, due to a common ground, can lead to a shift in the
potential. The maximum resistance of the trace of printed circuit board would be
0.1Ω. The typical current drawn by 100 LEDs on the board would be about 1-2mA
each. Even if half the LEDs were turned on at full brightness, a current of about
100mA would flow through. It results in a potential drop of 10mV across the board.
This large amount of current flowing through the circuit board brings in a 100%
72
error in measurement of potential. Since we had only 14 LEDs on the board, the
error is about 14% in the current measurement, i.e. 140µA through each LED. From
our current-voltage data, it corresponds to an error of about 20mV in the turn-
potential.
To sum up the error from electronics that is computed above, we find that the source
of error from the printed circuit board is much larger than from the electrical
components. It is still small smaller than the possible error from working electrode.
In order to improve the design of this circuit board the common ground was
eliminated and two separate grounds were used for analog and digital circuits. Some
measurements made with the improved design of circuit board show promising
results (not shown here). Since the absence of a reference electrode in the circuit
makes it impossible to measure the actual potential between working electrode and
the electrolyte, the above factors led to the development of version 2 of the screening
method.
Error from the electronics in combinatorial measurement (version 2)
The measurement of turn-on potential for catalysts could now be done at a current of
30µA instead of 450µA since the problem of a common ground in the circuit is
solved in version 2. From the individual measurements, this amount of current seems
very reasonable for significant kinetic activity at the electrode.
73
The possible sources of error from the electrical circuit used in measurement of turn-
on potential, at a current of 30 µA through the cell, are listed here.
1. Current-measuring resistor, R = 1000Ω (of 1% tolerance).
Voltage drop across the resistor at the current where LEDs turn on = (30µA) x
(1000Ω) = 30mV. Given 1% tolerance of 1000Ω resistor, the maximum error in
current measurement is 0.3µA. Calculations from individual I-V curves of different
catalysts (Figure 30) show that the maximum error in the measurement of turn-on
potential from this resistor is about 0.2mV.
Calculation of the above error (an example):
(∆V/∆I)
at 30µA
V/µA x 0.3µA = (1.036-1.035)/(30.78-28.58) V/µA x 0.3µA
= 0.13mV
2. Op-amp, AD620A on the middle board as the instrumentation amplifier. It has an
input offset voltage of about 185µV and an output offset voltage of maximum 2mV.
It has a gain of 9.98 with an error of 1.3%. The voltage at the input of this
instrumentation amplifier is given by
V
input at 620
= I
R
(R ± R
error
),
where I
R
= current through the resistor R. Thus,
V
input at 620
= I
R
(1000Ω ± 1%)
74
3. Op-amp, LM324A, on the top board that functions as a comparator. It has an input
offset voltage of 3mV. The input voltage V+ at the comparator is given by
V+ = gain (V
input

at 620
± V
input offset at 620
) ± V
output offset at 620
Thus, V+ = (9.98 ± 1.3%)[I
R
(1000Ω ± 1%) ± 185µV] ± 2mV
≈ 9.98[I
R
(1000Ω ± 2.3%) ± 185µV] ± 2mV
≈ 9.98[I
R
(1000Ω ± 2.3%)] ± 1.85mV ± 2mV
≈ 9.98[I
R
(1000Ω ± 2.3%)] ± 3.85mV
Also, V- = V- ± V
input offset at 324
The LED turns OFF when V+ = V-, thus
V- = 9.98[I
R
(1000Ω ± 2.3%)] ± 3.85mV ± 3mV
= 9.98[I
R
(1000Ω ± 2.3%)] ± 6.85mV
We set this V- to 300mV in our experiment such that this potential drop across a
1000Ω resistor gives a current of 30µA. Thus, we get about a 5% error in the current,
I
R
= 30µA, i.e. a maximum error of 1.5µA in the current. From our I-V curves, a 5%
error in current at 30µA gives a maximum error of about 0.65mV in the
measurement of turn-on potential.
4. The op-amp, AD8625 that functions as a potentiostat, has an input offset voltage
of 50µV. Thus, there is an error of 50µV in the measurement of cell potential.
The input current of this op-amp AD8625 is a maximum of 1.0pA that can be
considered negligible in comparison to the reasonable conductance (about 1.0 Ω
–1
m
-
1
) of electrolyte solution. The impedance of the silver-silver chloride reference
75
electrode is probably not so large as to make the voltage drop across it significant.
There may also be errors in the voltage applied to the cell. We neglect the errors
from sourcemeter or from the power supply for V- since the system is almost linear
in behavior. Thus we assume a zero offset for the voltage applied to the
electrochemical cell.
The above calculations give a total maximum error in electronics as about 1.0mV
(0.2mV + 0.65mV + 0.05mV), in the measurement of turn-on potential at a current
of 30µA. The estimated error is reduced to a very large extent in version 2 of
screening method. The error from electronics in version 2 is very small (1mV vs.
50mV) compared to the variation in working electrode from cell-to-cell. Thus, the
combinatorial screening method using visual output in version 2 should prove to be a
very sensitive screening approach for metal catalysts as long as the catalysts are
uniform in surface composition from one cell to another.
2.4 Measurement
Version 1
The catalyst library, supported on carbon paper (TCP: Toray carbon paper) was
sandwiched between the aluminum plate and the Teflon block and sealed using
silicone gasket (Figure 26a). A 0.1M solution of sodium perchlorate (NaClO
4
) in de-
ionized water was used as the electrolyte. Each cell was filled with 0.75 ml of this
solution. The electrochemical circuit was driven from 0-3V in steps of 5-6mV in a
76
stair configuration at a scan rate of 100mV/s. The data was recorded manually as a
digital movie (30 frames/s) of the LEDs turning on within the voltage sweep. The
sequence in which the LEDs turn on is proportional to the electrochemical activity of
metal catalysts for the reaction in the cells.
Version 2
The same above procedure was followed for measurement of current in version 2 of
the screening method. Due to a larger displacement of electrolyte in cells (as a result
of plastic casing around the wires), only 0.4 ml of the electrolyte solution was added
in each well. To the electrolyte solution, a pinch of sodium chloride solution was
added to maintain the stability of Ag-AgCl reference electrodes. The slight presence
of chloride ions seems to help maintain the silver chloride salt on the silver wires.
The voltage was swept from 0 to 2V at a rate of 100mV/s.
3. Results and discussion
Various experiments were conducted to study the catalytic activity of metal particles
using the combinatorial screening method. A few of these experiments are described
here to highlight the results of screening method.
77
Version 1
3.1 Blank library (no metal catalyst) as reference
A blank carbon paper library (used as received), with no metal catalyst was screened.
The driving voltage for the op-amps was 8 V. The offset voltage was set to 10 mV
that corresponds to a current of about 450µA (across a 22Ω resistor) flowing through
a cell. The voltage across the cells was swept from 0-3V at a rate of 100mV/s. The
results shown here (Figure 31) are for 14 cells, though the electronic board was
designed for a 4x4 array of cells. Two of the sixteen LEDs were accidentally short-
circuit in the process of experimentation.
The LEDs turn on at about 2.82V and the spread in their turn-on voltage is about
20mV. This turn-on potential for carbon paper (TCP) containing cells, serves as a
reference for defining the activity of cells containing metal particles as catalysts. It
also brings out the limit of resolution of the experiment suggesting that we can
distinguish between catalytic activity in two cells that have a difference in turn-on
potential of at least 20mV.
3.2 Screening of metal catalysts
(i) A library of ruthenium and iridium metal particles was prepared such that the pure
metals were compared to a 4:1 atomic mixture of Ru and Ir. A mixture of two metals
was prepared by taking parts by volume of the precursor salt solutions (2.5mM
solutions). The carbon paper (TCP), calcined and reduced under the same conditions
78
as the metal salts on the carbon paper, was left blank in one row to serve as a
reference for comparison. The offset voltage was set to 10mV. The operational
amplifiers were driven at 8.0V for this experiment. The voltage across the
electrochemical cells was swept from 0-3 volts at a rate of 100mV/s.
The sequence of catalytic activity is observed (Figure 32) to be in the following
order: Ru > Ru/Ir (80/20) > Ir > TCP. The turn-on potential for cells containing Ru
metal particles is about 2.3V. The turn-on potential for the cells containing TCP (no
metal catalyst) was about 2.6V. This value is about 200 mV lower than that obtained
in the above experiment, probably since the carbon paper here was heat treatment
during catalyst preparation. The difference in the turn-on potential for more active
Ru catalyst and TCP is about 300mV, as analyzed from the movie of sequence
recorded on camera. The difference in the turn-on potentials of metal catalysts, Ru,
Ru/Ir and Ir is much smaller (tens of mV), as seen on analysis of individual frames of
the sequence. This method works reasonably to screen the electrochemical activity of
metal catalysts in a combinatorial array, towards the oxidation of water.
(ii) A combinatorial library containing iridium and ruthenium metal particles was
prepared. The design of this library has a row of pure metal each and a row of 1:1
atomic mixture of Ru and Ir metal particles. The 4th row was left blank with no
catalyst to serve as reference TCP for the experiment. The driving voltage for the op-
amps was set to 2.5V and the offset voltage was set to 10mV. The voltage was swept
from 0-3V at a rate of 100mV/s.
79
The sequence of activity of catalysts was observed as: Ru and Ru/Ir (50/50) > Ir >
carbon paper (Figure 33). The cells with Ru and Ru/Ir (50/50) metal particles appear
to turn on at about the same potential of 2.4V. The cells with Ir catalyst turn on a
100mV later, at 2.5V. The TCP reference cells have a turn-on potential of about
2.8V. The turn-on potentials are in close agreement with those obtained from
individual measurements on cells containing Ru and TCP (Figure 34), at a current of
about 450µA through a cell. A discussion on these measurements follows in the next
paragraph.
(iii) Current-voltage curves were plotted for some of the electrochemical cells in an
attempt to obtain the turn-on potentials of individual cells in the combinatorial setup.
The data was obtained by video recording of current and voltage values observed on
the sourcemeter during the voltage sweep. A platinum wire of the same dimensions
was used as the counter electrode and a silver wire was used as reference electrode
for the measurements. The data plot is an average of measurements from different
cells of the same catalyst.
The current-potential curves of Ru metal particles are shown in Figure 34 with
reference to TCP. In the combinatorial experiments, a 10mV offset in voltage
suggests a current of about 450µA (across a 22Ω resistor) flowing through a cell.
This magnitude of current parallels a potential of about 2.35V for the cells with Ru
metal particles and about 2.85V for TCP. The results from combinatorial screening
80
show about the same potentials for the turn-on of LEDs in the cells. This shows that
the results from combinatorial screening experiments are in close agreement with the
individual current measurements. The above magnitude of current relates to a turn-
on potential of about 1.25V vs. a standard Ag-AgCl reference electrode for the Ru
metal catalyst, and about 1.5V for TCP (Chapter 1, Figure 20). Thus, the above
experiment suggests that the overpotential is reduced by about 250mV with a
ruthenium catalyst on surface of carbon paper for the reaction in question.
A direct comparison with other studies in literature on the activity of metal catalysts,
for oxidation of water at the anode, is difficult to make since the activity of catalyst
depends not only on its composition but also on its method of preparation. Catalysts
of the same composition prepared by the use of different reducing agents have shown
very different activity as direct methanol fuel cell anode catalysts.
16
Synthesis of
catalysts in situ in large arrays results in low surface area materials while those
prepared in bulk form as high surface area catalysts. High throughput screening
methods use the first method of synthesis because of speed and smaller volumes of
solvent used. We can only draw comparison of our combinatorial measurements to
our individual measurements and justify the screening method.
3.3 Screening of electrolytes
A library of TCP was prepared by the same procedure of calcination followed by
reduction as used for preparation of catalyst metal particles. Aqueous solutions of
81
sodium perchlorate (0.1M) and tetramethylammonium bromide (0.1M) were
prepared for screening using this method. The voltage was swept from 0-3V at a rate
of 100mV/s. The offset voltage was set to 15mV.
The LEDs of the cells containing the N(Me)
4
Br electrolyte turned on at about 2.3V
while those with NaClO
4
turned on at about 2.9-3.0V (Figure 35). This was expected
because the oxidation of bromide ion precedes the oxidation of water for the same
amount of current flowing through the cells. The two-electron oxidation of bromide
ion (Br
-
) to bromine gas (Br
2
) occurs at about 1.09V vs. NHE (normal hydrogen
electrode) whereas reduction of ClO
4
-
occurs at about 1.19V. The oxidation of water
occurs at a thermodynamic potential of 1.23V vs. NHE. This experiment shows that
the screening method works well for different electrolytes as well. Other aqueous
electrolytes could be screened and evaluated in a rapid manner using this method.
Version 2
The above preliminary screening results led to the development of an improved
version (version 2) of screening method for combinatorial screening of metal
catalysts towards the oxidation of water. A few results that highlight the method and
its use for the above are described here.
82
3.4 Screening of metal catalysts
Many combinatorial libraries containing metal catalysts were screened for their
catalytic activity towards the oxidation of water. Results from one of the experiments
from this method of screening are described in details. The library was prepared as
described before, by the thermal reduction of metal salts of Pt, Ir and Ru on carbon
paper. For this particular experiment, the voltage was swept from 0 to 1.5 V at a rate
of 100mV/s. The offset voltage for red LEDs to turn off was set to 300mV that
amounts to a current of 30µA through each cell.
The results indicate that the order in which red LEDs turn off is Ir > Ru > Pt (Figure
36). The turn-on potentials obtained from experiment are Ir: 0.85V, Ru: 0.95V, Pt:
1.05 V and TCP: 1.20V. Thus, the turn-on potential at a current of 30µA through the
cell is lowest for the iridium metal catalyst on the surface of carbon paper. The order
of catalytic activity of metal particles towards the oxidation of water is given by the
above results. The difference in the turn-on voltage at the above current for any two
catalysts is about 100mV. The results agree very well with the individual
measurements of current through such cells (Figure 36). The screening method
works well within the error limits (8-10mV) to distinguish two catalysts that are only
100mV apart in their turn-on potentials at a very low current of 30µA through the
cell. Depending on the kinetics of the reaction, a higher or lower current value can be
used to screen catalysts for a reaction.
83
The results from a library of blank carbon paper (used as received), under the same
experimental conditions, support the findings from screening a catalyst library. The
turn-off potential (about 1.2V) at a current of 30µA through all 16 cells containing
just carbon paper (Figure 37) agrees with that observed in the catalyst library
described above. The standard deviation in turn-on voltage is of the order of 50mV,
which is the same as observed in a blank area of catalyst library. The chance that
thermal treatment to the carbon paper brings in surface modification, if any, can be
ruled out from the above finding.
Thus, we can say that the combinatorial screening method described here works well
as a quick process to rate the activity of metal catalysts for oxidation of water. The
selected good catalysts can be analyzed further by detailed individual measurements.
The method is shown to work as a fast, reliable, qualitative preliminary screening of
catalysts. Considering the variation in results from individual measurements of
different cells of the same catalyst in the combinatorial setup (Figure 38) our results
from combinatorial screening using this method are in good agreement. The
flickering observed in the LEDs, before they finally turn off also relates very well to
the minor fluctuations in current, from 1mV to the next, in current-voltage curves
obtained from individual measurements. In comparison to thermal imaging method
and the first version of this method, the activity of metal catalysts is screened more
clearly and consistently by this method. We have not yet tried the method on a
library of mixed metal alloys as catalysts for the reaction but expect it to be working
for the same.
84
Some improvements that we suggest to this method include the use of a better and
more stable reference electrode. Ag-AgCl microelectrodes can be obtained and used
for more consistent results. It would add to the cost of measurement but would
certainly be durable and reliable for screening multiple libraries in a short time. The
electronic boards designed for this method have a layout for thin tubing to each cell
that allows the use of a gas to purge into the solution. This would be very useful not
just to purge the electrolyte solution but also to study the effect of adsorbed gases at
the surface of catalysts. The preparation of catalyst library starting from metal
precursor salts can be explored and different methods can be tried. We chose thermal
treatment because it gives uniform and stable surfaces and is a quick method for
preparation of metal catalysts on the surface of carbon paper. Finally, a robotic
system for this method of combinatorial screening can be developed to speed up the
entire process and quick screen multiple combinations of metals from across the
periodic table.
4. Summary
A combinatorial method using visual output of LEDs is developed for screening
metal catalysts towards the oxidation of water. It started as an improvement in the
amplification of current, close to the turn-potential for electrochemical activity, over
the thermal output method described in Chapter 1 of this document. It involves the
85
use of potentiostats and ammeters in the circuit for each cell. We call it a sensitive
digital ammeter. The difficult part in the design of the system is not just keeping a
low cost but also building the electronics in a very small area that is limited by the
pitch of the cells in this combinatorial experiment.
The first version of the screening method gives the turn-on potentials for metal
catalysts at a current of 450µA (about 15mA/cm
2
) through the cell. The activity of
metal catalysts is rated as Ru > Ru/Ir > Ir with reference to the carbon paper. Similar
results are obtained for two different atomic ratios of Ru and Ir catalysts. The
difference in turn-on potentials for the above catalysts is about 50-100mV.
The second version of the screening method incorporates a reference electrode in
each cell with the use of a potentiostat. The measurements are now like in a true
electrochemical cell, unlike the floating electrode system (varying voltage of counter
electrode with current) in version 1 of the method. The activity of metal catalysts, at
a current of 30µA (about 1mA/cm2) through the cell, is rated as Ir > Ru > Pt with
reference to the carbon paper. The difference in turn-on potentials for the above
catalysts is about 100mV.
The combinatorial setup in version 2 is extremely useful for screening metal
catalysts for the oxidation of water. It makes use of multiple potentiostats and
ammeters, and LEDs for visual output of the results, all assembled on circuit boards
the size of a 12x8 combinatorial lab-array. It costs less than a single potentiostat used
86
in laboratory for electrochemical measurements but does about 100 times the work.
Thus it is a very efficient and economical method for screening the activity of metal
catalysts. The measurements can be made even faster with the use of a digital
readout board for parallel readout to a computer. We are in the process of developing
this kind of board. Also, the use of standard Ag/AgCl reference microelectrodes
would add to the stability of the system.
The resolution of the method is about ±20mV in the measurement of turn-on
potential at a current density of about 1mA/cm
2
. This limit is set more by the
inhomogeneous distribution of metal catalyst on carbon paper that works as the
working electrode of the cells. The preparation of metal catalyst on the surface of
carbon paper results in nanoparticles of metal that do have uniform size and
distribution but it seems like the catalytic activity is not truly uniform across the
cells. The most likely source for this cell-to-cell variation for the same set of
electrodes is the carbon paper itself. In other words we could argue that the screening
method using digital ammeters is so sensitive that it can tell a very small difference
in activity of the same catalyst across cells.
87
Meas. Sci. Technol., 16 (2005) 54–59
Figure 22 Automated serial photoelectrochemical screening to characterize the
activity of supported Au clusters for water oxidation and CO oxidation. The cell
containing counter and reference electrodes traverses the library illuminating each
sample and measuring the photoelectrochemical property.
88
J. Comb. Chem., 6 (2004) 149-158
Figure 23 Schematic of the electrochemical control system developed for the
combinatorial electrochemical screening of catalysts of direct methanol fuel cells.
The modules depicted above are the computer for data acquisition (top), a 64-
channel current follower (center), a potentiostat (bottom left), a triangular sweep
generator (bottom right), and an electrochemical array cell (bottom center).
89
Figure 24 Layout of version 1 of electrochemical combinatorial screening. The
schematic is shown for one electrochemical cell from the combinatorial experiment.
R
L
: load resistor in series with the LED
V
-
: input voltage to amplifier from waveform generator
V
+
: input voltage to amplifier from across R in series with electrochemical cell
90
Figure 25 Illustrates the basic principle of screening method that uses a sensitive
digital ammeter electronic circuit. The two input voltages to the amplifier are shown
as a function of time in the top part of figure. The middle plot shows the rate of
output voltage with respect to the two input voltages. The bottom plot shows the
light intensity from LED as a function of current through the cell.
91
(a) (b)
(c)
Figure 26 Images from equipment used in version 1 of the screening method. (a) The
8x12 combinatorial array is shown here in the Teflon block with 96 wells that hold
the electrolyte solution. The catalyst library on carbon paper is sandwiched between
Teflon block and aluminum plate. (b) Electronic equipment, like the waveform
generator, the sourcemeter and oscilloscope. (c) Top face of the electronic board
with surface-mount red LEDs in a 4x4 array.
92
Figure 27 Layout of the design of system in version 2 of combinatorial screening
method. The schematic is shown for one cell from the combinatorial experiment.
93
(a)
(b)
Figure 28: Continued
94
(c)
Figure 28 Images of the three printed circuit boards used to build a sensitive digital
ammeter in version 2 of the combinatorial screening method using visual output.
Board (a) is used to interface with the electrochemical cell, Board (b) has the
potentiostats to measure current through the cell and Board (c) has the comparators
and LEDs (on the other side) for visual output. A dime is placed on the boards for
estimation of size.
95
(a)
(b)
Figure 29 Images from the setup used in version 2 of the combinatorial screening
method using visual output. The circuit is complete in (a) while in (b) the counter
and reference electrodes are seen encased in plastic tubing before lowering into the
electrolyte wells with working electrode at the bottom of the well.
96
Figure 30 Current-voltage curves from individual measurements in electrochemical
cells in the combinatorial setup. The dashed line is drawn at a current of about 30
µA, where the catalytic activity is compared in the cells. The scan rate is 100mV/s.
— Iridium
— Ruthenium
— Platinum
— TCP
97
Figure 31 Images from screening of a library of carbon paper (TCP) by version 1 of
the method. The potential at which the LED turns ‘on’, is defined as the turn-on
potential for the cell at that current density. A turn-on voltage of 2.82V is obtained
for the cells with carbon paper. The maximum spread observed in the turn-on voltage
of all cells is about ±10mV.
98

(a) (b) (c)

(d) (e)
Ru/Ir (80/20) Ru/Ir (80/20) Ru/Ir (80/20) Ru/Ir (80/20)
Ir Ir Ir Ir
Ru Ru Ru Ru
TCP TCP
Figure 32 Images from screening of a catalyst library of metal particles by version 1
of the method. The images are at (a) 2.27V, (b) 2.33V, (c) 2.36V, (d) 2.4V and (e)
2.6V during a voltage sweep from 0-3V at a rate of100 mV/s. The sequence of
catalytic activity towards the oxidation of water is Ru > Ru/Ir (80/20) > Ir > TCP.
99
(a) (b) (c)
Ru Ru Ru Ru
Ru/Ir (50/50) Ru/Ir (50/50) Ru/Ir (50/50) Ru/Ir (50/50)
Ir Ir Ir Ir
TCP TCP
Figure 33 Images from screening of a catalyst library of metal particles by version 1
of the method. The images are at potentials of (a) 2.4V, (b) 2.5V and (c) 2.8V during
a voltage sweep from 0-3V at a rate of 100mV/s. The sequence of catalytic activity
towards the oxidation of water is Ru > Ru/Ir (50/50) > Ir with reference to carbon
paper.
100
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 0.5 1 1.5 2 2.5 3
potential (volts)
current (mA)
carbon paper
ruthenium catalyst
Figure 34 Current-potential (averaged) curves obtained from recording the values in
individual electrochemical cells in version 1 of the method. The potential is reported
versus Ag-AgCl standard reference electrode. The Ru metal particles have greater
kinetic activity than TCP throughout the scan from 0-3V at 100mV/s.
101
(a) (b)
NaClO
4
NaClO
4
NaClO
4
NaClO
4
N(CH
3
)
4
Br N(CH
3
)
4
Br N(CH
3
)
4
Br N(CH
3
)
4
Br
NaClO
4
NaClO
4
NaClO
4
NaClO
4
N(CH
3
)
4
Br N(CH
3
)
4
Br
Figure 35 Images from screening of electrolytes, tetramethylammonium bromide
[N(CH
3
)
4
Br] and sodium perchlorate [NaClO
4
] by version 1 of the method. The
images are at (a) 2.3 V and (b) 3.0 V from a scan of 0-3V at 100mV/s. The oxidation
of bromide ion clearly precedes the oxidation of water.
102

Ir Ir Pt Pt Ru Ru TCP TCP
Ir Ir Pt Pt Ru Ru TCP TCP
Figure 36 Images from screening of a catalyst library of metal particles by version 2
of the method. The potential at which the LED turns ‘off’ is measured here vs. Ag-
AgCl reference electrode. The sequence of catalytic activity at a current of 30µA
through each cell is Ir > Ru > Pt > TCP. It is in good agreement with that obtained
from measurements in individual cells using a standard reference electrode (shown in
graph). The voltage was scanned from 0-1.5V at 100mV/s.
0.2V 0.6V 0.87V
0.98V 1.06V
1.14V
0.87V
V
1.36V
0.98V 1.06V
103

Figure 37 Images from screening a library of TCP (Toray carbon paper) by version 2
of the method. The turn-on potential, at a current of about 30µA through the cell (red
LED), is 1.2V. It is lower at lower values of current (green LEDs). The voltage scan
rate is 100mV/s.
0V 0.96V 1.2V
104

(a) (b)
Figure 38 (a) Current-voltage curves obtained from individual measurements in four
cells, all containing metal particles as catalyst. (b) The spread in turn-on voltage (of
the order of 15-60mV) at a current of 30µA is evident here. Potentials are reported
versus Ag-AgCl reference electrode. The voltage was scanned from 0-1.5V at
100mV/s.
Ir catalyst
Ru catalyst
Pt catalyst
105
Chapter 2 References
1. Hegemeyer A., Strasser P., Volpe A. F., Jr., High-Throughput Screening in Chemical Catalysis, Wiley-VCH, Weinheim, (2004), 273.
2. Jiang R., Chu D., J. Electroanal. Chem., 527 (2002), 137.
3. Baeck S. H., Jaramillo T. F., Brandli C., McFarlan E. W., J. Comb. Chem., 4 (2002), 563.
4. Yudin A. K., Siu T., Curr. Opin. Chem. Bio., 5 (2001), 269.
5. Sullivan M. G., Utomo H., Fagan P. J., Ward M. D., Anal. Chem., 71 (1999), 4369.
6. Warren C. J., Haushalter R. C., Matsiev L., U.S. Patent No. 6187164, (2001).
7. U.S. Patent No. 6682837, (2004); 6498121, (2003); 657965, (2003).
8. (a) Baeck S. H., Jaramillo T. F., Kleiman-Shwarsctein A., McFarland E. W., Meas. Sci. Technol., 16 (2005), 54; (b) Jaramillo T. F., Baeck S.
H., Kleiman-Shwarsctein A., McFarland E. W., Macromol. Rapid Commun., 25 (2004), 297.
9. Hintsche R., Albers J., Bernt H., Eder A. E., Electroanalysis, 12 (2000), 660.
10. Guerin S., Hayden B. E., Lee C. E., Mormiche C., Owen J. R., Russell A. E., Theobald B., Thompsett D., J. Comb. Chem., 6 (2004), 149.
11. Fei Z., Hudson J. L., J. Phys. Chem., 100 (1996), 18986.
12. Fei Z., Hudson J. L., J. Phys. Chem. B, 101 (1997), 10356.
13. Spong A. D., Vitins G., Guerin S., Hayden B. E., Russell A. E., Owen J. R., J. Power Sources, 119-121 (2003), 778.
14. Liu R., Smotkin E.S., J. Electroanal. Chem., 535 (2002), 49.
15. Diaz-Morales R. R., Liu R., Fachini E., Chen G., Segre C. U., Martinez A., Cabrera C., Smotkin E. S., J. Electrochem. Soc., 151 (2004),
A1314.
16. Chan B. C., Liu R., Jambunathan K., Zhang H., Chen G., Mallouk T. E., Smotkin E. S., J. Electrochem. Soc., 152 (2005), A594.
106
Chapter 3: Cyclometalated Platinum and Iridium
complexes with non-innocent ligands
1. Introduction
The coordination chemistry of transition metal complexes of the redox active 1,2-
dioxolene ligands has been extensively studied in the last twenty-five years
1,2,3,4,5,6
.
Part of the interest in these complexes stems from the fact that the transition metal
and ligand frontier orbitals are close in energy that results in strong mixing between
these orbitals such that the assignment of oxidation states to individual metal and
ligand components is difficult. Such ligands are termed as ‘non-innocent’ ligands.
The redox isomers of the ligands, shown below, exhibit the potential for forming
complexes that may exist in a number of electronic states due to the combined
electrochemical activity of the metal and the ligand. The metal complexes show low-
energy charge-transfer transitions that are fully allowed and thereby intense. They
are also redox-switchable.
Scheme1
107
A number of applications have been listed that stem from fundamental studies on
non-innocent ligands and their metal-complexes. Redox-switchable electrochromic
dyes to modulate optical signals and smart windows to filter out infrared radiation
from visible light are some such examples.
7,8,9
In addition, these materials could find
use in organic solar cells as sensitizers due to their strong absorption extending into
the near-infrared region (700-900 nm).
10,11
The spectroelectrochemical properties of
ruthenium and osmium complexes with dioxolene ligands have been reported in
detail.
12,13,14,15
Many of these complexes have shown intense, low-energy transitions
that are redox switchable. The molecule with the low-energy transition has the
semiquinone form of the dioxolene ligand coordinated to the metal center.
There are fewer reports on the electronic structures of open-shell platinum and
iridium complexes of dioxolene ligands, than their Ru and Os counterparts. In the
previous reports of Pt and Ir complexes where dioxolene is the ancillary ligand,
triarylphosphines or cyclooctadienes were used to fill out the metal coordination
sphere.
16,17,18
The semiquinone form of the ligand was formed by the chemical
oxidation of the catecholate and the complex was found to be unstable at room
temperature, in some cases.
19,20
A stable platinum complex
16
formed by the
electrochemical oxidation of catecholate (diamagnetic) to the semiquinone
(paramagnetic) form showed a red shift in absorbance. A square-planar
bis(semiquinone) complex
21
of platinum(II) has also been studied that is diamagnetic
and shows intense absorption bands in the near-infrared region. Platinum(II)
complexes containing 2,2’-bipyridine as the cyclometalating ligand and a chelated
108
dithiolene/dioxolene ligand were reported as efficient and stable photosensitizers for
singlet molecular oxygen production.
22,23
These complexes were neutral and
diamagnetic. The catecholate form of a five-coordinate triphos-iridium(III)
compound
24,25,26
has been studied for the uptake of dioxygen, both experimentally and
theoretically. The electrochemical oxidation of this complex results in the
semiquinone form of the ligand. A bis(catechol)-iridium(IV) complex
27
with 1,5-
cyclooctadiene ligand was characterized with an intense absorption band at very low
energy.
Recently a wide variety of iridium
28
and platinum
29
complexes with cyclometalated-
ligands have been reported as emissive materials in organic light emitting diodes
(OLEDs). The C
^
N ligands were used to tune the electronic properties of metal
complexes.
30, 31
With the use of different cyclometalating ligands on the metal we
could possibly be able to tune the electronic properties of the metal-dioxolene
complex, giving materials that absorb at long wavelengths, with high oscillator
strengths.
We report here the synthesis and characterization of cyclometalated (C
^
N)
complexes of iridium and platinum with 3,5-di-tert-butylcatechol (Figure 39). The
electronic transitions and the electrochemical behavior of these open-shell molecules
are presented here both from experimental observations and theoretical calculations.
109
2. Experimental section
2.1 Materials and Synthesis
Iridium(III) chloride, IrCl
3
and potassium tetrachloroplatinate(II), K
2
PtCl
4
were used
as purchased from Next Chimica. 3,5-di-tert-butylcatechol (dtbcat), p-tolylpyridine
(tpy), 2-phenyl quinoline (pq) and tetramethylammonium hydroxide (25 wt%
solution in methanol) were purchased from Aldrich Chemical Company and used
without further purification. 2,4-difluorophenylpyridine (dfppy) was synthesized by
Suzuki coupling reaction of the commercially available di-fluoroboronic acid with
the bromopyridine. The reference dyes, IR-27 and IR-140 for near-infrared emission
studies were also purchased from Aldrich Chemical Company.
(tpy-Ir-sq). The iridium(III) µ-dichloro-bridged dimer, [Ir(C
^
N)
2
(µ-Cl)]
2
was made
by thermal coupling of the Ir(III) chloride (IrCl
3
.nH
2
O) salt with a slight excess of 2
equivalents of p-tolyl pyridine (tpy) in a 3:1 mixture of ethoxyethanol and water at
80°C. The mixture was refluxed overnight and the yellow precipitate of product was
filtered, washed and dried.
The 3,5-di-tert-butylcatechol (3,5-DTBCat) was coupled to the chloro-bridged
iridium dimer in the presence of the base tetramethyl ammonium hydroxide. To a
solution of the dimer and a slight excess of 3,5-DTBCat in dichloroethane:ethanol
(5:1), the base was added drop wise while purging with nitrogen. The color changed
110
gradually from yellow to olive-green. The mixture was stirred at RT and exposed to
air in about one hour. The stirring was stopped after 3 days and the solvent
evaporated. The product was purified by silica gel column chromatography using
dichloromethane as solvent.
The pure complex was isolated as an olive green solid in about 90% yield. FAB
+
-
MS: m/z 749.27. Elemental analysis: C 61.18, H 5.46, N 3.66 (found); C 60.94, H
5.38, N 3.74 (calculated).
1
H-NMR (250 MHz, in d-CHCl
3
): broad signals in
aromatic and aliphatic regions. Some of it was sublimed at about 220°C in vacuum.
(dfppy-Pt-sq). The platinum(II) monochloro complex, [Pt(C
^
N)(HC
^
N)(Cl)] was
made as above by thermal coupling of potassium tetrachloroplatinate (K
2
PtCl
4
) salt
with 2,4-diflorophenylpyridine (dfppy). The light yellow precipitate of product was
filtered, washed and dried.
The 3,5-di-tert-butylcatechol was coupled to the above complex in the presence of
the base tetramethyl ammonium hydroxide. To a solution of the monochloro
complex and a slight excess of the catechol ligand in a 5:1 mixture of 1,2-
dichloroethane and ethanol, the base was added drop wise while purging with
nitrogen. The color changed gradually from yellow to olive-green. The mixture was
stirred at RT and exposed to air in about one hour. The stirring was stopped after 3
days and the solvent evaporated. The product was purified by silica gel column
chromatography using dichloromethane as solvent.
111
The pure complex was isolated as a green-brown solid in about 90% yield. EI-MS:
m/z 605. Elemental analysis: C 49.37, H 3.98, N 2.33 (found); C 49.59, H 4.33, N
2.31 (calculated).
1
H-NMR (250 MHz, in d-CHCl
3
): broad signals in aromatic and
aliphatic regions.
(pq-Pt-sq). The platinum(II) monochloro complex, [Pt(C
^
N)(HC
^
N)(Cl)] was made
as above by thermal coupling of potassium tetrachloroplatinate (K
2
PtCl
4
) salt with 2-
phenylquinoline (pq). The red precipitate of product was filtered, washed and dried.
The 3,5-di-tert-butylcatechol was coupled to the above complex in the presence of
the base tetramethyl ammonium hydroxide. To a solution of the monochloro
complex and a slight excess of the catechol ligand in a 5:1 mixture of 1,2-
dichloroethane and ethanol, the base was added drop wise while purging with
nitrogen. The color changed gradually from red to purple to black. The mixture was
stirred at RT and exposed to air in about one hour. The stirring was stopped after 3
days and the solvent evaporated. The product was purified by silica gel column
chromatography using dichloromethane as solvent.
The pure complex was isolated as a purple-black solid in about 90% yield. EI-MS:
m/z 618.
1
H-NMR (250 MHz, in d-CHCl
3
): broad signals in aromatic and aliphatic
regions.
112
2.2 Spectroscopic measurements
I
H-NMR spectra were recorded on Bruker AC 250 MHz instrument. The elemental
analysis was done at the Microanalysis Laboratory at the University of Illinois,
Urbana-Champaign. The mass spectrometry for the tpy-Ir-sq complex in the FAB
(fast atom bombardment) ionization mode was performed at California Institute of
Technology, Pasadena on a JEOL machine using nitrooctophenyl ether as the matrix.
The solid-probe mass spectra for the dfppy-Pt-sq and pq-Pt-sq complexes were taken
with Hewlett-Packard GC/MS (gas chromatography/mass spectrometry) instrument
with electron impact ionization and model 5973 mass selective detector.
EPR spectra were recorded using an X-band Bruker EMX spectrometer (controlled
by Bruker Win EPR Software v. 3.0) equipped with a rectangular cavity working in
the TE
102
mode. Low temperature measurements at 80K were conducted with an
Oxford continuous-flow helium cryostat (temperature range 3.6 – 300 K). All spectra
were acquired in toluene solution.
The UV-visible absorption spectra were recorded at room temperature in
dichloromethane solution on a Hewlett-Packard 4853 diode array spectrophotometer.
The near-infrared absorption spectra were recorded at room temperature in
dichloromethane solution on a Nicolet 860 Magna Series FTIR (fourier transform
infrared) using a quartz beam splitter and a DTGS-KBr (deuterated triglycine sulfate
– potassium bromide) detector. Steady-state emission spectra were measured using a
Photon Technology International QuantaMaster model C-60 spectrofluorimeter. The
113
room temperature measurements were done both in dichloromethane and in 2-
methyltetrahydrofuran solutions that were freshly distilled over sodium. The low
temperature (77K) measurements were done only in the 2-methyltetrahydrofuran
solutions. The solutions were degassed under nitrogen before measurement.
Solutions of IR-27 and IR-140 in dichloromethane were used as a reference in the
near-infrared region.
2.3 X-ray diffraction methods
Diffraction data for tpy-Ir-sq and pq-Pt-sq complexes were collected on a Bruker
SMART APEX CCD diffractometer with graphite-monochromated Mo Kα radiation
(λ = 0.71073 Å). The cell parameters were obtained from the least-squares
refinement of the spots (from 60 collected frames) using the SMART program. A
hemisphere of the crystal was collected up to a resolution of 0.75 Å, and the intensity
data was processed using the “Saint Plus” program. All calculations for structure
determination were carried out using the SHELXTL package (version 5.1). Initial
atomic positions were located by Patterson methods using XS, and the structures
were refined by least-squares methods using SHELX 93 with 7149 independent
reflections within the range of φ = 1.60 to 27.49 (completeness 93.7%) for tpy-Ir-sq
and 4749 independent reflections within the range of φ = 1.54 to 25.68
(completeness 99.4%) for pq-Pt-sq. Empirical absorptions were applied by using
SADABS. Calculated hydrogen positions were input and refined in a riding manner
114
along with the attached carbons. A summary of the refinement details and the
resulting factors are given in the Appendices.
Diffraction data for the dfppy-Pt-sq platinum complex was collected on a Bruker
Kappa/ApexII system equipped with graphite monochromated Mo radiation. The
data crystal was mounted using oil (Parantone-N, Exxon) to a 0.3 mm cryo-loop
(Hampton Research) with the (0 1 -1) scattering planes roughly normal to the spindle
axis. All crystals examined exhibited non-merohedral twinning (roughly imposing a
pseudo two-fold along the a-axis). Two distinct cells were identified using APEX2
(Bruker, 2004) and Cell_Now (Sheldrick, 2004). Four frame series were integrated
and filtered for statistical outliers using SAINT (Bruker, 2001) then corrected for
absorption by integration using SHELXTL/XPREP (Bruker, 2001) before using
SAINT/TWINABS (Bruker, 2001) to sort, merge, and scale the combined data.
Combined unit cell parameters were determined from both components using SAINT
(Bruker, 2001). The twin law by rows was (1 0 0.296), (0 -1 0), (0 0 -1). Non-
overlapping reflections from the primary orientation were used for phasing.
Combined data with complete or no overlap were used for refinement. No decay
correction was applied.
Structure was phased by dual space methods (Schneider, 2002). Systematic
conditions suggested the ambiguous space group. The space group choice was
confirmed by successful convergence of the full-matrix least-squares refinement on
F^2^. The highest peaks in the final difference Fourier map were in the vicinity of
115
atoms C21_1, C1_3, and C6_2; the final map had no other significant features. A
final analysis of variance between observed and calculated structure factors showed
little dependence on amplitude or resolution; however, reflections in the h1l planes
were sensitive to minor changes in the proposed model. A summary of the
refinement details and the resulting factors are given in the supplementary material.
2.4 Electrochemical methods
Cyclic voltammetry and differential pulsed voltammetry were performed using an
EG&G potentiostat/galvanostat model 283. Anhydrous acetonitrile (Aldrich) and
N,N-di-methylformamide (Aldrich) were used as solvents under a nitrogen
atmosphere, and 0.1M tetra(n-butyl)ammonium hexafluorophosphate was used as the
supporting electrolyte. A glassy carbon rod was used as the working electrode, a
platinum wire was used as the counter electrode, and a silver/silver chloride
microelectrode was used as the reference electrode. The redox potentials are reported
relative to a ferrocene/ferrocenium (Cp
2
Fe/Cp
2
Fe
+
) redox couple.
2.5 Theoretical methods
Geometry optimizations were performed using the hybrid DFT functional B3LYP as
implemented by the Jaguar 6.0 program package.
32
This DFT functional utilizes the
Becke three-parameter functional
33
(B3) combined with the correlation functional of
Lee, Yang, and Par
34
(LYP), and is known to produce good descriptions of reaction
profiles for transition metal containing compounds.
35,36
The metals were described by
116
the Wadt and Hay
37
core-valence (relativistic) effective core potential (treating the
valence electrons explicitly) using the LACVP basis set with the valence double-
contraction of the basis functions, LACVP**. All electrons were used for all other
elements using a modified variant of Pople’s
38
6-31G** basis set, where the six d
functions have been reduced to five. All DFT calculations were calculated as
unrestricted doublets.
Excited states were investigated theoretically using time dependent DFT (TD-DFT)
calculations with the Gaussian 03 program.
39
To investigate the low-energy
excitations in the Pt and Ir complexes, TD-DFT calculations were performed using
the B3LYP hybrid functional
33,34
together with the standard LanL2DZ basis set and
ECP specification, which uses the D95V valence double-zeta basis set
40
for the light
elements, and the Los Alamos ECP plus DZ
37a
on the metals.
3. Results and Discussion
3.1 Synthesis and characterization
The C
^
N chloride-complexes of Ir and Pt were treated with base and 3,5-di-tert-
butylcatechol (3,5-dtbcat) to form the dark colored complexes of the dioxolene
ligand. The reaction was carried out under nitrogen to avoid oxidation of the
deprotonated catechol species. The organic base, tetramethyl ammonium hydroxide
[N(Me)
4
OH] has good solubility in methanol and thereby miscible with the catechol
117
in solution. This avoids the use of thallium acetate that has previously been used for
the synthesis of ruthenium-dioxolene complexes.
15
The dark green to purple-red to
black-looking metal complexes of both platinum and iridium were worked up and
purified in ambient conditions and are found to be stable. The iridium complex is
sublimable in vacuum at about 220°C.
Note: Iridium complexes with different dioxolene-type ligands were attempted by
two different preparation methods. Reaction of iridium dimer with alizarin (1,2-
dihydroxy-9,10-anthraquinone) and coumarin (6,7-dihydroxy-4-methylcoumarin)
failed to proceed in the forward direction by either method to give a substantial and
stable product.
The crystals for the compounds were grown at room temperature over a period of
one week by diffusion of hexane into a dichloromethane solution. The iridium
compound crystals are olive green in color while the platinum ones are green-brown
or purple-red in appearance. They are prismatic in shape, the dfppy-Pt-sq is platy in
appearance.
The structures for the complexes were determined by X-ray crystallography. The
thermal ellipsoid views of the metal complexes are shown in Figure 40. The C-O
bond lengths in the semiquinone ligand of the complexes are 1.28-1.30Å (C1-O1 =
1.295(5)Å and 1.285(7)Å, C2-O2 = 1.291(5)Å and 1.296(7)Å for tpy-Ir-sq and
dfppy-Pt-sq, respectively). This bond distance is consistent with the C-O length
118
found in the semiquinone ligand in a large number of quinone complexes.
6
The two
C-O lengths are different in the pq-Pt-sq complex, one corresponding to the
semiquinone distance (1.27(2) Å) and the other to the catechol distance (1.33(2) Å).
The six-carbon ring (C1 through C6) has non-aromatic character with bond distances
consistent with other metal complexes of the same semiquinone ligand.
21,41
The C1-
C2 bond length within the chelate ring is 1.447(6)Å for tpy-Ir-sq and 1.444(7)Å for
dfppy-Pt-sq complex. This bond distance corresponds to the semiquinone form of the
ligand in comparison to the 1.40Å bond length for the same two carbons in a
catecholate ligand.
6
A slightly longer C1-C2 bond length (1.49(2)Å) is found for the
pq-Pt-sq complex, again suggests the mixed semiquinone-catechol form of the
ligand.
In the dfppy-Pt-sq complex, mirror symmetry was imposed on two independent
molecules related separated by one-half unit cell length along the unique b-axis
(Figure 40). The stacked dimers have an inter-planar spacing of 3.4 Å while the
closest Pt-Pt distance is 3.47 Å. The metal-metal interaction in the crystal is very
weak, however, similar structures in related Pt(II) complexes lead to dimer or
excimer structures in their excited state.
42
There was no such stacking observed in the
pq-Pt-sq complex.
The crystal structure data confirms the presence of semiquinone form of the
dioxolene ligand bound to the metal center in the iridium and platinum complexes.
119
3.2 EPR spectra
Previous reports of metal complexes of platinum and iridium with the dioxolene
ligand, show that they are EPR active, with g-values close to that of a free electron.
22,
23, 24, 25, 30
The iridium and platinum complexes, tpy-Ir-sq and dfppy-Pt-sq, as isolated
in ambient conditions, appear as a sharp radical signal centered at g = 1.987 and g =
2.003, respectively in the room-temperature EPR spectra in toluene. This leads us to
conclude that the compounds are paramagnetic in nature and that the catechol ligand
is in the semiquinone form as a radical anion. The g-values are comparable to those
observed for other platinum- and iridium-dioxolene complexes.
The heavy metal complexes of platinum, iridium, ruthenium and osmium exhibit
anisotropy that is observed at low temperatures. The reported line width from peak to
peak is less than 10 Gauss.
19
Most of them do not show any coupling features
expected from hyperfine splitting caused by the interaction of the unpaired electron
with the metal nucleus. There is no detectable coupling even to phosphorous atoms
in compounds of platinum and iridium with triphenylphosphines and 1,2-dioxolene
type ligands,
16,24
consistent with preferential localization of the unpaired electron on
the semiquinone ligand. The ruthenium complex
14
(bpy)
2
Ru(dtbsq) shows axially
symmetric EPR at 77K that lead the authors to conclude that the molecular orbital
containing the unpaired electron is partially localized on the metal and thus gives it
somewhat of a Ru(III) ground state character. In the related osmium complex
13
(bpy)
2
Os(dtbsq), rhombic structure associated with low-spin d
5
Os(III) in an
octahedral environment was observed from the EPR spectrum at 77K. Two
120
components at g
1
= 2.448 and g
2
= 1.71 were seen but g
3
, the third component at high
field, was reported unobserved. There has been no mention of any coupling features
observed for the above ruthenium or osmium complexes.
At 80K, in glassy toluene, a rhombic spectrum (Figure 41) is obtained for the Ir-
complex with g
1
= 2.035, g
2
= 1.987, g
3
= 1.935 with peak-to-peak separation of
about 10 Gauss. The parameters for the Pt-complex (Figure 41) are g
1
= 2.042, g
2
=
2.006, g
3
= 1.958. The anisotropy reflects lower symmetry of electronic environment
around the metal centers. The g-value and the small g-spread indicate that the p-
orbital contribution from the ligand is greater than the d-orbital from the metal and
thus the unpaired electron is localized mainly on the ligand. The low-spin d
5
metal-
complexes, on the other hand, exhibit an even larger anisotropy with a large g-spread
suggesting the delocalization of the unpaired electron on the metal.
43
The line width
observed here corresponds to that observed for iridium(III) and platinum(II)
complexes
19
of dioxolene type ligands.
No resolvable hyperfine features are observed. The hyperfine splitting is not seen,
neither due to the proton at C-4 of the o-semiquinone ligand nor due to the metal
nuclei (
191
Ir or
193
Ir I=3/2,
195
Pt I=1/2). This agrees with the previously reported
absence of coupling features in similar metal complexes.
The symmetry observations from EPR spectra suggest that the ground-state
electronic structures of both Ru- and Os-complexes have contribution from the metal
121
orbitals but it is significantly more in the Os-complex than in the Ru-complex.
Similarly we can say that the mixing of metal and ligand orbitals in both the iridium
and platinum complexes results in delocalization of the unpaired electron that gives
them a mixed ground state electronic structure but with the unpaired electron being
localized mainly on the ligand.
3.3 Electronic spectra
The absorption spectra of both the iridium and platinum complexes (Figure 42 and
Figure 43) show intense bands in the ultraviolet region between 250 and 350 nm.
These high-energy bands can be assigned primarily to the allowed
1
(π-π
*
) transitions
of the C
^
N cyclometalating ligand.
30
The intensity of absorption (Table 2) is higher
for the iridium complex than for the platinum complexes because of the presence of
twice the number of C
^
N ligands in the iridium complex. The low-energy transition
peaked between 600 and 650 nm is intense and broad. This band extends to 1200 nm
in the near-infrared region. The semiquinone ligand (3,5-DTBSQ) itself gives a
similar spectrum. A broad low-energy transition centered at 650 nm (ε
max
of about
500 M
-1
cm
-1
) is observed in the spectrum of 3,5-di-tert-butyl-o-benzosemiquinone in
a basic DMF solution.
44
The coupling of the ligand to the metal complex increases
the intensity of absorption in this region because of greater charge transfer caused by
the mixing of metal and ligand orbitals (see the molecular modeling study below).
122
The charge transfer bands in the low energy region are red-shifted in wavelength in
the platinum complexes in comparison to the iridium complex. It seems to be a result
of the metal more than the C
^
N ligand since there is not much of a difference in the
absorption maxima of methyl and di-fluoro substituted C
^
N rings. In a comparison of
the two platinum complexes (Figure 43) the absorption bands are red-shifted in the
complex with 2-phenylquinoline because of an extension in the size of conjugated π-
system. Similar shifts have been observed in the tuning of energy by varying
substituents or ring systems in cyclometalated iridium and platinum complexes.
30, 31
The complexes were examined for photoluminescence at room temperature and at
77K in 2-methyltetrahydrofuran. No visible emission was observed in the visible or
near-infrared region at any temperature.
3.4 Electrochemistry
The electrochemical properties of the complexes were examined using cyclic
voltammetry and differential-pulse voltammetry. The redox data is given in Table 2.
The potentials that are reported here were measured relative to standard Ag/AgCl
reference electrode and are adjusted to internal ferrocene reference (ferrocene
measured 0.436V vs. Ag/AgCl) for literature report.
The tpy-Ir-sq complex shows four redox couples in the range of –2.5V to +1.5V (vs.
Fc
+
/Fc couple). Part of the cyclic voltammogram is shown in Figure 44. The
123
dioxolene ligand is in the semiquinone oxidation state at the beginning of the
experiment. The most negative couple, observed around –2.68V (not shown in
figure), has been observed from our studies of other complexes with the same C
^
N
ligands
28,30
and has been assigned as the reduction potential for the metal bound tpy
ligand. The other negative redox peak at –0.88V is a fully reversible one electron
process. It is attributed to the catechol/semiquinone couple. The analogous
ruthenium complex, Ru(bpy)
2
(dtbcat) shows this couple at –0.91V vs. Fc
+
/Fc in
dichloroethane.
14
The semiquinone/catechol couple for the 3,5-di-tert-butylcatechol
ligand in the same solvent, acetonitrile is observed at –1.75V.
44
This implies that the
ligand-based reduction is easier when the ligand is coordinated to the metal complex.
The positive potential process at +0.08V for the Ir-complex is quasi-reversible. This
implies that the oxidation of the semiquinone form of the ligand to the quinone state
leaves it unstable in the medium and leads to the formation of some other species.
This new species grows in on repeated cycling. The ligand-based redox couples are
observed even on multiple cycles. This kind of slow decomposition pathway has
been observed at room temperature in other Ir(III), Co(II) and Rh(III) catecholate
complexes.
24, 25, 26
The unstable quinone form results in the formation of a di-solvento
complex of acetonitrile and a free quinone (Q). The chemical process responsible for
this decomposition in [(triphos)M
III
(DTBCat)]
3+
, where M = Ir, Rh, Co, accelerated
with an increase in temperature and is not observed at low temperatures.
124
MeCN
[(tpy)
2
Ir
III
(dtbq)] [(tpy)
2
Ir
III
(NCMe)
2
]
+
+ Q
The most positive couple observed at a potential of +0.90V is reversible. It relates to
the oxidation of bis-acetonitrile-iridium moiety in the solvent-coordinated cationic
species. It could correspond to the Ir(III)/Ir(IV) couple.
Similar data is observed for cyclic voltammetry on the dfppy-Pt-sq and pq-Pt-sq
platinum complexes (Figure 44). The separation in the two ligand-based couples is
about 0.8V or 0.86V for the Pt-complexes versus 0.96V for the Ir-complex. This
separation is about 0.8V in the electrochemical process of the ligand, 3,5-di-tert-
butylcatechol (3,5-DTBCat).
44
Since the oxidation of either one of these complexes
is irreversible (leading to the formation of a new species), this difference is not a
clear measure of the HOMO-LUMO energy gap. Since square planar Pt(III) metal
center is susceptible to nucleophilic attack by solvents, this redox couple is usually
irreversible. It may well be occurring at the same time as the sq/q process, which we
also believe to be irreversible in these complexes, under the conditions that the
electrochemistry is carried out here. The most negative potential that is localized on
the cyclometalating ligand is lower for the Pt-complexes than the Ir-complex. The
redox properties are influenced by the presence of two electron-withdrawing fluorine
atoms on the phenyl rings and the greater stabilization of negative charge on the
more delocalized π-orbital system that makes C
^
N an easier to reduce ligand.
125
The addition of ferrocene (as an internal reference) to the solution for
electrochemistry of the Ir-complex results in a visible change in color. This suggests
that the ferrocene gets chemically oxidized to the ferrocenium salt and the Ir-
complex is reduced. The two species either form a new complex or decompose.
Further cyclic voltammetry on this solution results in gradual disappearance of the
previously observed redox peaks. Similar behavior is observed for the Pt-complex.
Our speculation is that the metal-complex in its semiquinone form undergoes a
ligand-based oxidation that results in the formation of a quinone and a di-solvento
complex. Only the ligand-based reduction from semiquinone to catechol is a fully
reversible couple.
3.5 DFT calculations
Calculations were carried out on Ir-sq and on both isomers of Pt-sq (referred to as Pt-
sq
1
and Pt-sq
2
, Scheme 2). The results of the Pt-sq calculations showed very little
difference between the two isomers, with an energy difference of only 0.1 kcal/mol.
Thus, they should be considered isoenergetic within the margin of error of the
calculations. The change in spin density was insignificant (root mean square of
change = 0.01 electrons) while the change in orbital energies was about 1 kcal/mol
on average.
126
Pt-sq
1
Pt-sq
2
Scheme 2
Calculations were also done on the model compounds of the two complexes that use
simplified (less-substituted) analogs of the metal complexes for the calculations,
where the methyl or fluoro groups on the phenylpyridine moieties and the tert-butyl
groups on the semiquinone moieties are replaced with hydrogens. This significantly
reduces the size and consequently the computational cost of the systems. There is no
significant difference in the spin density in the model systems.
The spin densities in the calculated complexes are shown in Figure 45. For both
metal complexes, the spin density is centered mainly on the semiquinone ligand,
only a small metal contribution. The calculated mulliken spin populations show the
presence of 0.95 electrons on the semiquinone in the Ir complex, and 0.94 electrons
in the Pt complexes. In both cases, ~0.04 electrons reside on the metal, with the rest
are on the other ligands. This indicates that the metals should be considered Pt
II
and
Ir
III
complexes with an open-shell semiquinone ligand, which supports our
observations from the EPR spectra. Furthermore, the spin density is in agreement
with the spin density calculated for the isolated ligand 3,5-DTBSQ, located mostly
on the oxygen atoms of the ligand.
45
127
Molecular orbital pictures, for the Ir-sq (Figure 48) and Pt-sq (Figure 49) complexes,
of the different energy levels mainly involved in the redox and excitation processes
obtained by the calculations, are shown for the β-electron. The difference in energy
levels for the α- and β-electrons (see Figure 46) are listed in Table 3. It should be
noted that the HOMO (highest occupied molecular orbital) of the α-electron (the α-
HOMO) does not necessarily have the same symmetry as the LUMO of the β-
electron (the β-LUMO), due to orbital reordering. Though the symmetry of the α-
HOMO matches that of the β-LUMO in the platinum complexes, this is not true in
the iridium complex. In the iridium complex, the two highest occupied α-molecular
orbitals (α-HOMO and α-HOMO-1) are nearly degenerate (the energy difference is
less than 2 kcal/mol). The α-HOMO corresponds in symmetry to the β-HOMO,
while the α-HOMO-1 corresponds to the β-LUMO.
Initial analysis of the molecular orbitals suggest that the lowest energy transition
should be from the β–HOMO to the β–LUMO, which has a calculated energy
difference lower than the α-HOMO to α-LUMO transition. However, the calculated
energy difference in the different orbitals does not correspond to the lowest
measured absorbance peak for either compound. Consequently, time dependent
density functional (TD-DFT) calculations were performed on Ir-sq and Pt-sq
complexes in an attempt to explain the experimentally observed electronic behavior
of the two metal complexes.
128
3.6 TD-DFT calculations
The transition energies obtained from calculations on both open-shell complexes are
shown in Figure 47 for both complexes. The calculated absorption peak positions are
in close agreement with those in the measured spectrum for each complex.
The calculations provide a list of the electronic transitions that contribute to each of
the excited states, the oscillator strength of the transition to an excited state and the
expansion coefficient that relates to the percent contribution of the different
excitations to the particular excited state (Table 4). The results show that the lowest
energy excitations come from the β-molecular orbitals, in accordance with the orbital
energy differences discussed above.
In the iridium complex in dichloromethane solvent, the transition at a wavelength of
571 nm is the most favorable low energy transition with oscillator strength of about
0.09. This corresponds to the measured molar absorption maximum at 594 nm for the
analogous experimental complex. The calculations show that this transition comes
mainly from the β-HOMO-2 to the β-LUMO excitation. The orbital pictures (Figure
48) show a good degree of overlap in the iridium metal d-orbitals of the two
molecular orbitals. Both the β-HOMO and the β-HOMO-1 have very poor orbital
overlap with the β-LUMO and thus the excited state has almost no contribution from
these excitations. This leads us to conclude that the electronic transition in the red to
near-infrared region is primarily a HOMO-2  LUMO excitation of the β-electron
of the iridium complex.
129
The theoretical calculations were done on the two conformational isomers of the
platinum complex in dichloromethane solvent. The complex with the catechol ligand
flipped along the horizontal axis is labeled Pt-sq
2
. In the platinum complex, the
electronic transition from the β-HOMO-1 molecular orbital to the β-LUMO
molecular orbital contributes most significantly to the absorption at a wavelength of
592 nm for Pt-sq
1
and the β-HOMO-2 molecular orbital to the β-LUMO molecular
orbital at 604 nm for Pt-sq
2
. The β-HOMO-1 molecular orbital of Pt-sq
1
identifies
with the β-HOMO-2 molecular orbital of Pt-sq
2
. This excitation results from a good
orbital overlap (Figure 49). Most of the electron density is centered on the
semiquinone ligand, and some on the metal center. For both isomers, the β-HOMO
has poorer orbital overlap with the β-LUMO that results in a very small percent
contribution to the excited states (less than 10%). Similarly, the β-HOMO-2 has
almost no overlap with the β-LUMO since the metal d-orbitals are orthogonal to
each other in the two orbitals of Pt-sq. The molecular orbital pictures that correspond
to the excitation energy of transitions clearly indicate that the lowest energy
transition is a β-HOMO-1  β-LUMO excitation or a β-HOMO-2  β-LUMO
excitation and not a HOMO  LUMO excitation (of either spin).
Another excited state transition of significant oscillator strength was calculated at
wavelengths of 494 nm (f = 0.10) in Pt-sq
1
and 526 nm (f = 0.21) in Pt-sq
2
. The
major contribution to this state comes from the β-HOMO-3  β-LUMO excitation.
Yet another excited state transition (at 476 nm in Pt-sq
1
and at 445 nm in Pt-sq
2
) that
130
is of significant strength (0.1 and 0.06) results mainly from a α-HOMO to α-LUMO
excitation. The calculations show a not so intense, low energy transition in the near-
infrared region for both Ir-sq (758 nm, 0.0045 oscillator strength) and Pt-sq (840 nm
and 877 nm, 0.003 oscillator strength) complexes (Figure 49). This transition
involves the β-HOMO-1 and β-LUMO of Ir-sq and primarily the β-HOMO and β-
LUMO of Pt-sq. The poor orbital overlap explains the lower oscillator strength. The
calculated low energy transition corresponds to the tail of the absorption band
observed in the electronic spectra of the two complexes.
It should be noted that despite minor discrepancies the calculations suggest that two
isomers in Pt-sq complex are not significantly different in their low energy electronic
excitations. Also, the model system works to a certain extent in our theoretical
understanding of the electronic structure of compounds. A comparative analysis of
the simplified model system with the full system suggests that the molecular orbitals
that contribute significantly to the excited states are the same in density for both
systems. There is a clear difference in the two systems in their calculated excitation
energies in the low energy region of the spectra. In our results on both complexes,
the model system is lower in absolute energy than the full system. Nevertheless, the
interpretation of electronic structure of the complexes is the same from either system.
Thus, the theoretical calculations show that the low-energy electronic transitions
observed in the open-shell iridium and platinum complexes are a result of excitations
of β-electrons from a HOMO-n (n is an integer, n ≥ 1) to the LUMO. This suggests
that the relaxation of the excited β-electron from the LUMO into the filled molecular
131
orbitals could occur through a series of rapid internal conversion processes, leading
to no observable emission in the red to near-infrared region of the electromagnetic
spectrum. Transient absorption spectroscopy of the complexes in the picosecond to
femtosecond range could support the above argument.
4. Summary
The synthesis of iridium (tpy-Ir-sq) and platinum (dfppy-Pt-sq and pq-Pt-sq) neutral
complexes was achieved by coupling the catechol ligand to the cyclometalated
complex in the presence of a base under ambient conditions. The third row transition
metal complexes were characterized by crystallography. The bond lengths of the
catechol ligand indicate that it is in the semiquinone form in the two complexes. This
observation is also supported by the electronic configuration as determined by
density functional theory calculations. The low-energy transitions and the rhombic
EPR spectra suggest that the unpaired electron resides mainly on the semiquinone
ligand with Ir(III) and Pt(II) as the metal oxidation states. The reversible redox
couple of semiquinone and catechol, and the density functional theory calculations
support the localization of charge on the ligand. The electrochemical oxidation
results in solvent-coordinated complexes implying the poor stability of the quinone
complexes. The low energy metal-to-ligand charge-transfer transitions calculated
from time-dependent density functional theory calculations overlap well with the
observed absorptions of the two open-shell molecules. The calculations provide a
132
good picture of the molecular orbitals and of the difference in orbital energies
showing that the beta-electron excitation is favored over the unpaired alpha-electron
in both the complexes. This vertical excitation and a possible internal relaxation help
us understand the lack of luminescence in the visible to near infrared region of the
spectrum. The rapid internal conversion observed for these complexes suggests that
they will not be useful as light absorbing or sensitizing materials in solar cells, since
internal conversion will likely deactivate the excited state faster than charge
separation.
133
tpy-Ir-sq
dfppy-Pt-sq pq-Pt-sq
Figure 39 Chemical structures of iridium and platinum complexes.
134
(a)
(b)
Figure 40: Continued
135
(c)
(d)
Figure 40 Thermal ellipsiodal views of (a) the tpy-Ir-sq complex, (b) the pq-Pt-sq
and (c) the dfppy-Pt-sq complex. Also shown (d) is the packing diagram of dfppy-Pt-
sq in a unit cell.
136
Figure 41 Low temperature EPR spectra of the iridium and platinum complexes
measured at 80K in glassy toluene.
137
Figure 42 Electronic spectra of tpy-Ir-sq and dfppy-Pt-sq complexes measured in
dichloromethane at room temperature. The molar absorbance is in units of M
-1
cm
-1
.
The inset shows the absorbance in the ultraviolet region of the spectra.
138
Figure 43 Electronic spectra of pq-Pt-sq and dfppy-Pt-sq complexes measured in
dichloromethane at room temperature. The molar absorbance is in units of M
-1
cm
-1
.
The inset shows the absorbance in the ultraviolet region of the spectra.
139
Figure 44 Cyclic voltammograms of tpy-Ir-sq, dfppy-Pt-sq and pq-Pt-sq complexes
measured at room temperature. The potentials are shown relative to the internal
reference couple Fc
+
/Fc. The solvent was acetonitile for the first two complexes, the
pq-complex was measured in N,N-di-methylformamide.
140
Figure 45 Spin densities calculated from the density functional theory method for the
Ir-sq (left) and Pt-sq (right) complexes. There is some spin density on the metal
center but is mostly on the semiquinone ligand.
141
Figure 46 Naming scheme used in this work for open-shell molecules.
142
(a)
(b)
Figure 47 Transition energies of (a) Ir-sq and (b) Pt-sq complexes obtained from TD-
DFT calculations shown along with the experimental electronic spectra. The
calculated transitions are shown for both the model compound and the full molecule.
The extinction coefficient is given in M
-1
cm
-1
.
— Observed
— Calculated
— Calculated,
model system
— Observed
— Calculated, Pt-sq
1
— Calculated, Pt-sq
2
— Calculated,
model system
143
Figure 48 β-molecular orbitals of Ir-sq complex obtained from TD-DFT calculations.
The orbitals for model compound are shown on right and those for the full complex
are on the left.
β-LUMO
β- HOMO
β- HOMO-1
β- HOMO-2
144
Figure 49 β-molecular orbitals of Pt-sq complex obtained from TD-DFT
calculations.
isomer 1 (full system) isomer 2 (full system) simplified system
β-LUMO
β- HOMO
β- HOMO-1
β- HOMO-2
145
Table 2 The electronic spectra and electrochemical data of iridium and platinum
dioxolene complexes.
Sample Electronic spectra
a
λ
max
/nm (ε/10
-3
M
-1
cm
-1
)
Electrochemical potentials
(V vs. Fc
+
/Fc)
b
tpy-Ir-sq 267 (36.7), 313 (21.2), 408 (4.27),
594 (3.07)
-2.68, -0.88, +0.08
qr
,
+0.90
ir
dfppy-Pt-sq 248 (30.2), 281 (15.2), 442 (6.00),
522 (3.05), 648 (3.08)
-2.34, -0.46, +0.34
qr
pq-Pt-sq 253 (34.1), 294 (23.4), 433 (4.71),
491 (5.62), 679 (2.85)
-2.36, -0.56, +0.30
qr
a: Dichloromethane solution, the molar absorption coefficients (ε) are given in
parentheses, measurements done at room temperature.
b: Cyclic voltammetry measured in acetonitrile, with 0.1M TBAP as supporting
electrolyte, at a scan rate of 100 mV/s, measured at room temperature. The potential
reported here is the average of anodic and cathodic peak potentials for a reversible
process, or the peak potential for an irreversible process. All potentials are reported
versus the ferrocenium/ferrocene (Fc
+
/Fc) couple. Unless otherwise noted, the redox
process is reversible.
qr: quasi-reversible; ir: irreversible
146
Table 3 Molecular orbital energy differences (in kcal/mol) in the ground state of the
Ir-sq and Pt-sq
1
complexes. The molecular orbitals that are involved in low energy
charge-transfer transitions (see TDDFT) are listed in the table.
Molecular orbitals
of Ir-sq
ΔE for the α-electron
(kcal/mol)
ΔE for the β-electron
(kcal/mol)
E(HOMO) – E(LUMO) 77.50 48.28
E(HOMO-1) – E(HOMO) 03.81 15.17
E(HOMO-2) – E(HOMO-1) 18.88 04.13
Molecular orbitals
of Pt-sq
1
ΔE for the α-electron
(kcal/mol)
ΔE for the β-electron
(kcal/mol)
E(HOMO) – E(LUMO) 75.56 58.52
E(HOMO-1) – E(HOMO) 18.11 08.35
E(HOMO-2) – E(HOMO-1) 9.89 4.28
E(HOMO-3) – E(HOMO-2) 00.32 1.28
The molecular orbitals that are involved in low energy charge-transfer transitions
(see TDDFT) are listed in the above table.
147
Table 4 Excitations in the Ir-sq and Pt-sq complexes that contribute to the charge-
transfer transition in the red to near infrared region along with their relative
contributions given by the expansion coefficients. The oscillator strength indicates
the strength of absorption at that wavelength.
Excitation
wavelength
(nm)
Excitation
energy
(eV)
Oscillator
strength, f
Excited state
(major contribution)
Expansion
coefficient
Ir-sq 571.54 2.1693 0.0918 HOMO-2  LUMO,
HOMO-3  LUMO
0.76590
0.51939
Ir-sq, model
system
625.61 1.9818 0.0980 HOMO-2  LUMO,
HOMO-3  LUMO
0.86547
0.39865
Pt-sq
1
591.77 2.0951 0.0409
HOMO-1  LUMO
0.92845
Pt-sq
2
604.31 2.0517 0.0272 HOMO-2  LUMO 0.90972
Pt-sq, model
system
667.46 1.8576 0.0578 HOMO-1  LUMO 0.89196
148
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151
Chapter 4: Cyclometalated Iridium dinuclear complex
1. Introduction
The electronic interactions in molecules in which two (or more) metal centers are
linked by a bridging ligand have been studied since the Creutz-Taube ion
1
that links
two ruthenium metals (Scheme 1). The interaction occurs because the d-electrons of
the metal ions are in d(π) orbitals which can effectively overlap with the π-acceptor
ligand and are therefore delocalized to a certain extent between both metals across
the conjugated bridge. This interaction results in a separation of the two metal-
centered redox potentials for metals that are apparently in chemically identical
environments. Oxidation of one metal center results in a change of electron density
that is communicated to the other across the bridging ligand; the second metal-ion
‘feels’ the additional positive charge and is therefore more difficult to oxidize than
the first.
Scheme 1
152
Conformation of the bridging ligand, particularly when the bridging ligand contains
a biphenyl-type linkage, can control the magnitude of metal-metal interaction. In
such a linkage there is low potential barrier to rotation about the central C-C bond.
The rotation about the central bond (dihedral twist angle) affects the extent of π-
delocalization between the two ends of the ligand. It is possible to alter the
conformation of a bridging ligand electrochemically if the bridging ligand is redox-
active. The catecholate dianion (cat) is well known to undergo two successive one-
electron oxidations to the semiquinone (sq) and then quinone (q) oxidation states in
many of its complexes.
Non-innocence, which occurs when metal-based and ligand-based redox orbitals are
similar in energy, has been known since the first dithiolene complexes of the Ni
triad.
2
Complexes of ruthenium
3,4,5,6,7,8,9,10,11,12,13,14,15,16
and osmium
17,18
have received
particular attention because of their rich electrochemical and spectroscopic properties
that allows the internal charge distribution to be studied in many different oxidation
states. The ruthenium and osmium complexes with bis-dioxolene bridging ligand
have shown very rich electrochemical and spectroscopic behavior. A large number of
ligand-centered and/or metal-centered redox processes and strong metal-to-ligand
charge-transfer transitions in the near-infrared region of the spectra have been
observed in these complexes. The bis-dioxolene bridging ligand can exist in five
oxidation states that are related by one-electron transfers.
153
J. Chem. Soc., Dalton Trans., 1994, 799.
Scheme 2
In the cat-cat and q-q oxidation states the central biphenyl unit is twisted (dihedral
angle greater than 0°) because of a formal single bond between the rings that allows
the two halves to rotate freely, but the intermediate sq-sq state is a diamagnetic (odd
electrons of the semiquinone radicals are paired) quinoidal structure with a double
bond between the phenyl rings that constrains the ligand to be planar (dihedral angle
near 0°). The geometry of the mixed-valence cat-sq and sq-q states is not obvious,
they may be planar with the odd electron delocalized over the entire bridging ligand
and chemically equivalent ends or may be twisted (decoupled) with chemically
distinct ends. The electronic interaction between the two metals is through the
bridging ligand and thus depends on the conformation of this ligand. The non-
innocent behavior in a dinuclear complex is an essential prerequisite for strong
metal-metal electronic coupling across the bridging ligand.
154
We studied the electronic properties of iridium and platinum complexes of dioxolene
ligand, reported in the previous chapter of this document. They exhibit low energy
absorption bands of high intensity in the red to near-infrared region of the electronic
spectrum. We extended our investigations to iridium metal complexes with a
bridging ligand based on two dioxolene sites. They are expected to have higher
intensity absorption bands that are red-shifted in energy compared to the
mononuclear complexes due to the introduction of two dioxolene ligands on metal
centers that are linked by a bridging ligand. The dinuclear complexes could find use
in organic solar cells as sensitizers because of their efficient photon absorption
extending into the near-infrared region (700-900 nm) and the potential for higher
quantum efficiency due to triplet absorption. We describe here the syntheses, spectral
and electronic properties of the iridium dinuclear complex (Figure 50) based on the
bis-catechol ligand 3,3’,4,4’-tetrahydroxybiphenyl and draw comparisons with the
mononuclear complex described in chapter 3 of this document.
2. Experimental section
2.1 Materials and Synthesis
Iridium(III) chloride, IrCl
3
was used as purchased from Next Chimica. p-
tolylpyridine (tpy), tetramethylammonium hydroxide (25 wt% solution in methanol),
palladium acetate (Pd(OAc)
2
), triphenyl phosphine (PPh
3
), 3,4-dimethoxyboronic
155
acid, 4-bromoveratrole, sodium carbonate and boron tribromide (1.0 M solution in
dichloromethane) were purchased from Aldrich Chemical Company and used
without further purification. The reference dyes, IR-27 and IR-140 for near-infrared
emission studies were also purchased from Aldrich Chemical Company.
Iridium dimer. The iridium(III) µ-dichloro-bridged dimer, [Ir(C
^
N)
2
(µ-Cl)]
2
was
made by thermal coupling of the Ir(III) chloride (IrCl
3
.nH
2
O) salt with a slight excess
of 2 equivalents of p-tolyl pyridine (tpy) in a 3:1 mixture of ethoxyethanol and water
at 80°C. The mixture was refluxed overnight and the yellow precipitate of product
was filtered, washed and dried.
Bridging ligand. A mixture of 3,4-dimethoxyboronic acid (1g) and 4-
bromoveratrole (1.5 equivalent) with triphenyl phosphine (0.2 equiv) and sodium
carbonate (4 equiv) in ethanol (20 ml) and toluene (120 ml) was purged well with
nitrogen. The catalyst, palladium acetate (1/20 parts) was added and the mixture was
kept under nitrogen. The mixture was refluxed overnight, cooled to RT and phase
separated using dichloromethane and water. The organic layer containing the
product was washed a few times, dried and then re-crystallized from ethanol.
The product, 3,3’,4,4’-tetramethoxy biphenyl was isolated as light yellow to brown
crystals in about 70-80% yield. EI-MS: m/z 274.
1
H-NMR (250 MHz, in d-CHCl
3
),
ppm: 7.10(d, 2H, 2.05 Hz), 7.06(dd, 2H, 2.39, 2.05 Hz), 6.92(d, 2H, 8.18 Hz), 3.95(s,
6H), 3.91(s, 6H).
156
The demethylation reaction for the tetramethoxy biphenyl was carried out under
nitrogen using boron tribromide (5-6 equiv) in a dichloromethane solution at –78°C.
The solution was warmed up to RT overnight and exposed to air to release the fumes
of hydrogen bromide. Then DI water, along with 1ml of saturated ammonium
chloride solution was slowly added to get a white precipitate that was filtered and
washed with water. The color turned to light pink when dry.
The 3,3’,4,4’-tetrahydroxy biphenyl was isolated as very light pink solid in near
100% yield. EI-MS: m/z 218.
1
H-NMR (250 MHz, in d-acetone), ppm: 7.10(d, 2H,
9.89 Hz), 6.18(d, 2H, 2.05 Hz), 6.00(dd, 2H, 2.05, 4.43 Hz). Analysis for C
12
H
10
O
4
:
found C 65.14, H 4.49, calculated C 66.05, H 4.62.
Iridium dinuclear complex. The 3,3’,4,4’-tetrahydroxy biphenyl was coupled to
the chloro-bridged iridium dimer in the presence of the base tetramethyl ammonium
hydroxide. To a solution of 3,3’,4,4’-tetrahydroxy biphenyl and the dimer (2 equiv)
in dichloroethane:ethanol (5:1), the base was added drop wise while purging with
nitrogen. The color changed gradually from yellow to dark olive-green. The mixture
was stirred at RT and exposed to air in about one hour. The stirring was stopped after
3 days and the solvent evaporated. The product was purified by silica gel column
chromatography using dichloromethane as solvent.
157
The pure complex was isolated as an olive green solid in about 90% yield. FAB
+
-
MS: m/z 1272. Elemental analysis for C
60
H
46
Ir
2
N
4
O
4
: C 54.91, H 3.64, N 4.11
(found); C 56.68, H 3.65, N 4.41 (calculated).
1
H-NMR (250 MHz, in d-CHCl
3
),
ppm: 8.34(d, 6Hz, d, 13Hz, 2H), 8.14(m, 2H), 7.78(m, 4H), 7.68(m, 4H), 7.48(m,
4H), 7.03(m, 6H), 6.77(d, 2H, 9Hz), 6.63(t, 4H, 6Hz, 9Hz), 6.03(s, 2H), 5.95(d, 2H,
4Hz), 2.05(d, 12H, 5.14Hz).
2.2 Spectroscopic measurements
The methods used for spectroscopic analysis were the same as in Chapter 3 of this
document. The mass spectrometry in the FAB ionization mode was performed at
University of California, Riverside on a VG-ZAB machine.
2.3 Electrochemical methods
The electrochemical analysis was performed using the methods described in Chapter
3.
2.4 Theoretical methods
The density functional theory (DFT) and the time-dependent density functional
theory (TD-DFT) calculations were done in the same manner as for the mononuclear
complexes described in Chapter 3.
158
3. Results and Discussion
3.1 Synthesis and characterization
The iridium dimer was synthesized by the method used before in the synthesis of
mononuclear iridium complexes described in Chapter 3 of this document. The dimer
is characterized by
1
H-NMR such that a comparison can be made with the final
product.
Suzuki coupling followed by the demethylation reaction
3,19,20
was used to synthesize
the bridging ligand (Figure 51). The tetramethoxy biphenyl compound is
characterized in agreement with previous results of the same compound.
21
The
tetrahydroxy biphenyl compound was stored under nitrogen to avoid oxidation of the
hydroxy groups. The absence of methyl peaks on the
1
H-NMR of the compound
indicates the complete conversion of methoxy to the hydroxy compound. The
structure is confirmed by elemental analysis.
The bridging ligand is coupled to the C
^
N chloride-complex of iridium in the
presence of a base to form the dark colored dinuclear iridium complex. The reaction
was carried out under nitrogen to avoid oxidation of the deprotonated catechol
species. The organic base, tetramethyl ammonium hydroxide [N(Me)
4
OH] has good
solubility in methanol and thus be easily miscible with the bridging ligand in
solution. This avoids the use of thallium acetate that has previously been used for the
159
synthesis of ruthenium-dioxolene complexes.
22
The olive-green product was worked
up and purified in ambient conditions and is found to be stable. Similar preparation
was used for the iridium mononuclear complex and has also been used for the
synthesis of an iridium binuclear catecholate complex with 3,4-
dihydroxybenzaldehydeazine as bridging ligand.
23
The aromatic region of the
1
H-
NMR spectrum (Figure 52) contains all the peaks from the iridium dimer and in
addition the peaks from the three different proton environments of the bridging
ligand. The aromatic protons add up to 32 and the aliphatic to 12, as expected. The
low chemical shifts of the protons from the bridging ligand suggest that the bridging
ligand is no longer aromatic. The fact that the complex is diamagnetic confirms that
the bridging ligand is in the semiquinone-semiquinone state carrying a 2- charge,
where the two unpaired electrons are paired to give an alkoxy-ketone structure. The
elemental analysis of the dinuclear complex gives low %C values. This has been
commonly observed for polynuclear complexes of heavy metals with extended,
highly aromatic ligands. We tried to grow crystals of the complex by slow
evaporation of a solution of it but failed in all our attempts.
3.2 Electrochemistry
The electrochemical properties of the complex are examined using cyclic
voltammetry. The redox data is given in Table 5. All potentials that are reported here
are measured vs. standard Ag/AgCl and adjusted to ferrocene reference for literature
report (ferrocene measured 0.436V vs. Ag/AgCl).
160
The dinuclear iridium complex shows five redox couples in the range of –2.5V to
+2.0V (vs. Fc
+
/Fc couple). The cyclic voltammogram is shown in Figure 53. The
bridging ligand is in the semiquinone-semiquinone oxidation state at the beginning
of the experiment. The most negative couple, observed around –2.92V (not shown in
figure) is independent of the type of ligand and has been known from our other
studies
24, 25
as the redox potential for one of the tolyl-pyridyl ligands (tpy/tpy
-
process). The two other negative redox peaks at –0.52V and –0.16V are fully
reversible ligand-based electron processes. They are attributed to the
catechol/semiquinone couple on the two halves of bridging ligand. Thus the
reduction proceeds through a mixed valence state semiquinone-catechol to form
catechol-catechol. The analogous ruthenium complex, [{Ru(bpy)
2
}(µ-
L){Ru(bpy)
2
}]
2+
where L = tetrahydroxy biphenyl, exhibits two reversible reductions
at –1.04V and –0.70V vs. Fc
+
/Fc in dichloromethane (Figure 54).
3
The separation
between the pair of reductions is nearly the same in both ruthenium (0.34V) and
iridium (0.36V) dinuclear complexes. This shows that the bridging ligand-based
redox chemistry is fairly independent of the transition metal center and the
cyclometalating ligands. The separation of 360 mV indicates a strong electronic
interaction between the two halves of the bridging ligand. The analogous osmium
complex, [{Os(bpy)
2
}(µ-L){Os(bpy)
2
}]
2+
where L = tetrahydroxy biphenyl, exhibits
two reversible reductions at –0.78V and –0.68V vs. Fc
+
/Fc in acetonitrile (Figure
54).
17
The reduced separation of 100 mV between the two reductions indicates that
the redox processes are predominantly metal-centered in the osmium complex,
161
unlike the ligand-centered reduction processes in ruthenium and iridium dinuclear
compounds. There was also a mention of the return waves changing in position and
intensity and even disappearing in some experiments making the reduction processes
irreversible. The authors ascribe it to deposition of the reduced form of the complex
onto the platinum electrode surface. The osmium complex was therefore formulated
with the metal as Os
III
and cat-cat state of the bridging ligand.
The first oxidation wave at +0.80V for the complex is quasi-reversible (the return
wave is of lower intensity than the outward wave) followed by a reversible oxidation
wave at +1.39V. This implies that the oxidation of the semiquinone state of the
bridging ligand to the quinone state leaves it unstable in the medium and leads to the
formation of some other species. This new species grows in on repeated cycling.
This kind of slow decomposition pathway is similar to the mononuclear iridium and
platinum complexes of catechol ligands. The pair of oxidations in the similar
ruthenium and osmium complexes has been reversible and substantially separated by
about 320 and 340 mV, respectively indicating that they are ligand-centered.
The separation of about 1V between the first redox couple and the irreversibility of
the oxidation process has both been observed in metal-catecholate complexes.
9, 26
Surprisingly, the separation between the first oxidation and the first reduction
potentials of the mononuclear and dinuclear iridium complexes is exactly the same
(0.96V). Considering the greater extent of π-conjugation in the bridging ligand
compared to the catechol ligand, it is expected that the HOMO-LUMO gap of the
162
semiquinone-semiquinone bridging ligand should be smaller resulting in a smaller
separation. The first oxidation process, not being a truly ligand-based process could
possibly justify the above observation. The very large separation of about 1.44V
observed in a dinuclear Osmium complex that has a lower extent of π-conjugation in
the bridging ligand (chloranilic acid) was also due to the oxidation being metal-
centered rather than being ligand-based.
18
3.3 Electronic spectroscopy
The absorption spectrum of the dinuclear iridium complex (Figure 55) shows an
intense band (ε = 117,000 M
-1
cm
-1
) in the ultraviolet region between 250 and 350
nm. This high-energy band can be assigned primarily to the allowed
1
(π-π
*
)
transitions of the four C
^
N cyclometalating ligands. The bridging ligand alone in the
sq-sq form with un-substituted phenyl rings shows an absorbance at about 400 nm.
27
The lower energy metal-to-ligand charge transfer transitions in the visible region of
the spectrum are quite intense (~10
4
M
-1
cm
-1
) for transitions occurring in this low
energy region. There is a very intense (ε = 32,000 M
-1
cm
-1
) and broad absorption
band in the near-infrared region at about 863 nm. This transition could be arising
from the mixing of the frontier orbitals of the metal (d(π) orbitals) and the ligand in
its semiquinone state (singly occupied molecular orbitals). This absorption band is
fully traced in the near-infrared region (Figure 56) using a near-infrared detector.
The tail of the intense, low-energy transition extends to about 1,600 nm. This band is
red-shifted from the mononuclear iridium complex [(tpy)
2
Ir(sq)] by about 5250 cm
-1
163
and has an extinction coefficient of ten times that of the band in the mononuclear
complex with one semiquinone moiety (Figure 57, Table 5). This large increase is
primarily due to the better electron accepting property of the bridging ligand than the
semiquinone alone but could also include the presence of some intra-ligand π-π
*
transitions. The long tail of this band on the low-energy side helps explain the above
statement.
A comparison with the ruthenium analog (Figure 58) of the dinuclear complex
(1,080 nm, ε = 37,000 M
-1
cm
-1
) shows that the low energy absorption band in iridium
dinuclear is very similar in shape and intensity but not as red-shifted.
3
Also, the
iridium complex shows a greater shift in the low energy band along with a larger
increase in intensity (5250 cm
-1
shift, about 10 times higher) from mononuclear to
dinuclear than the ruthenium complex (2,100 cm
-1
shift, 2.6 times increase). The
osmium analog (Figure 59) shows a low-energy transition at 961 nm (ε = 14,000 M
-
1
cm
-1
) that is red-shifted from its mononuclear complex by about 2,000 cm
-1
and
about 2.3 times higher in intensity. The difference in the electronic states of metal
complexes that are responsible for the low energy transitions brings out the above
differences.
A comparison of iridium, ruthenium and osmium complex shows that the electronic
properties of their dinuclear complexes are very similar while those of their
mononuclear complexes are significantly different. It suggests that the extensive
delocalization across the bridging ligand in the dinuclear complexes tunes the
164
electronic properties more significantly than the metal properties. In the mononuclear
complexes, it is the metal-dioxolene interaction, besides the cyclometalating ligand,
that tunes the electronic properties.
The iridium complex was examined for photoluminescence at room temperature and
at 77K in 2-methyltetrahydrofuran. No visible emission is observed in the visible or
near-infrared region at any temperature.
3.4 Theoretical calculations
Density functional theory calculations have been used to describe the electronic
structure of bis-dioxolene radical metal complexes of cobalt and chromium where
the bridging ligand was in a mixed-valence state.
19
They concluded on a fully
delocalized electronic structure of the mixed-valence system (sq-cat) that is
independent of the dihedral angle between the dioxolene planes. The two tert-butyl
groups on the phenyl rings keep the symmetry of the bis-dioxolene molecule.
We used time dependent density functional (TD-DFT) calculations to study the
ground and excited states of the iridium dinuclear complex. The calculations were
done on the less-substituted analog of the iridium complex, where the methyl groups
on the phenylpyridine moieties were replaced with hydrogens. This reduces the size
and consequently the computational cost of the systems.
165
The dinuclear iridium complex was optimized in two independent geometries giving
two nearly degenerate (about 0.4 kcal/mol different) minima with dihedral angles
between the two phenyl moieties of the bridging ligand of about 16° and 164°,
respectively, with an interconversion energy barrier of about 15 kcal/mol. These are
the two rotational isomers, cis and trans, with the cis being a little more stable than
the trans form. A total of 16 stereoisomers are possible. The two rotational isomers,
cis and trans are discussed here. The energy barrier between the two minima is not
high enough to prevent a fluctional behavior in solution at room temperature. This
could also explain our unsuccessful attempts at growing a crystal from a solution of
the complex. The dihedral angle being well under 45° (or over 135°) confirms that
there is π-conjugation in the bridging ligand and the molecule is in a singlet ground
state, as observed by its diamagnetic character.
In the trans-configuration of metal complex, the most favorable calculated transitions
are at wavelengths of 1146 nm (ΔE
HOMO-->LUMO
= 23.4 kcal/mol) and 740 nm (ΔE
HOMO-
4-->LUMO
= 53.1 kcal/mol) (Figure 60) with oscillator strengths of 0.46 and 0.22
respectively. The two calculated values of transitions for the trans-isomer are not
close to the observed low energy transition peak at 863 nm but do fall within the
broad transition band (Figure 62). The complex in the cis-configuration on the other
hand, results in most favorable low energy transition at 894 nm (Figure 61) with high
oscillator strength of 0.69. This value lies close to the peak of observed transition
band (at 863 nm) in the low energy region of the spectrum. The major contribution to
this excited state comes from HOMO to LUMO transition (ΔE = 28 kcal/mol). Yet
166
another transition was calculated at 664 nm that is of higher energy (ΔE
HOMO-4-->LUMO
= 56 kcal/mol) and lower oscillator strength (0.19). This value also overlaps with the
above observed transition band. The calculated transition in the visible region at
about 455 nm with oscillator strength of 0.035 corresponds to the observed transition
in the spectrum at 456 nm (Figure 62).
The electron density in the HOMO and LUMO of the cis or the trans isomer of
dinuclear iridium complex is centered on the bridging ligand with some metal
character. The theoretical calculations suggest that the cis isomer is the dominant
form.
Note: We made an attempt to synthesize the same dinuclear complex of platinum
(Scheme 3a). The reaction mixture suggests the formation of the product with an
absorbance peak at 730 nm in the near-infrared region. Either the product is unstable
in air or is a different state of the bridging ligand (eg. sq-cat or cat-cat) that the
purification loses this absorption band and there is no clear separation by column
chromatography. Another iridium dinuclear complex was attempted using a different
bridging ligand, 9-phenyl-2,3,7-trihydroxy-6-fluorene (Scheme 3b). The peak
integrations (37 aromatic protons and 12 aliphatic protons) in
1
H-NMR suggest the
product (dark green) is diamagnetic and thus in its fully reduced form with a net
positive charge. It undergoes an irreversible color change to brown on
electrochemical oxidation. The absorption bands at 686 nm and 939 nm in the low
167
energy region are no longer present. No further attempts were made to purify the
product and study the electronic properties.
(a) (b)
Scheme 3
4. Summary
The iridium dinuclear complex with the bis-dioxolene ligand was synthesized using
the preparation for metal-dioxolene complexes. It is characterized by
1
H-NMR as
diamagnetic and planar in the sq-sq state with a non-aromatic character of the phenyl
rings of the bridging ligand. The complex exhibits rich redox chemistry with two
reversible reductions that are bridging ligand-centered. The separation between two
peaks indicates a strong electronic interaction between the two metal centers through
the bridging ligand. The iridium complex shows very intense and broad transitions in
the near-infrared region of the spectrum. These are significantly red-shifted (by
5250cm
-1
) from the dioxolene iridium complex. The bis-dioxolene ligand in sq-sq
state (unpaired electrons are coupled) is a better electron-acceptor than the dioxolene
168
ligand in sq state. These transitions are assigned as metal d(π) to semiquinone metal-
to-ligand charge transfer transitions. There may be some overlapping intra-ligand π-
π
*
transitions that lead to the very high oscillator strength (ten times) compared to the
mononuclear iridium complex. The presence of isomers of the iridium complex with
very low energy barrier for conversion from one form to another is investigated by
time-dependent density functional theory calculations. It suggests that the cis isomer
is the dominant of the two rotational isomers since calculated values for the low
energy transitions of the cis isomer lie close to the observed electronic transitions.
The iridium dinuclear bis-dioxolene complex shows a much greater shift in
electronic properties from the iridium dioxolene complex in comparison to the very
similar ruthenium and osmium complexes reported earlier. The greater spin-orbit
coupling in iridium could be responsible. Also, the iridium complexes are neutral in
nature compared to the charged Ru and Os complexes. These materials should be
investigated for applications in organic solar cells as sensitizers. A more detailed
study on tuning the electronic properties of dinuclear metal complexes could follow
by varying the bridging ligand, the cyclometalating ligands and the transition metals.
169
Figure 50 Chemical structure of the iridium dinuclear complex.
170
Figure 51 Synthesis of the bridging ligand in the iridium dinuclear complex.
171

tpy-Ir-thbp
in CDCl3
on 03-22-05
filename:bhavirth
ppm
9.00 8.00 7.00 6.00 5.00 4.00 3.00 2.00 1.00 -0.00
File created:
Friday, March 25, 2005
10:17 AM
Bruker

tpy-Ir-thbp
in CDCl3
on 03-22-05
filename:bhavirth
ppm
8.00 7.00 6.00
ppm
# Start Stop Integral
2 8.43 8.26 2.05
2.05
3 8.19 8.08 2.02
2.02
4 7.87 7.74 4.23
4.23
5 7.74 7.59 4.29
4.29
6 7.54 7.42 4.14
4.14
7 7.13 6.95 6.24
6.24
8 6.82 6.72 1.98
1.98
9 6.69 6.55 3.94
3.94
10 6.09 5.99 1.93
1.93
11 5.98 5.90 1.84
1.84
Points 1D 8192
File created:
Friday, March 25, 2005
10:17 AM Bruker
Figure 52
1
H-NMR spectrum of the diamagnetic iridium dinuclear complex in d-
CHCl
3
measured at RT. The bottom figure shows the peak integrals in the aromatic
region relative to the 12 aliphatic protons.
172
Figure 53 Cyclic voltammogram of iridium dinuclear complex in acetonitrile at a
scan rate of 100 mV/s.
J. Chem. Soc., Dalton Trans., 2000, 3162.
Figure 54 Cyclic voltammograms of (a) Os dinuclear and (b) Ru dinuclear
complexes in acetonitrile at a scan rate of 200 mV/s.
173
Figure 55 Electronic absorption spectrum of the iridium complex in CH
2
Cl
2
shown in
the ultraviolet and visible region.
Figure 56 Electronic absorption spectrum of the iridium complex in CH
2
Cl
2
shown in
the near-infrared region (red curve) with an overlap of the peak from the visible
region (blue curve).
174
Figure 57 Electronic absorption spectrum of the dinuclear iridium complex
compared to the mononuclear iridium complex with the dioxolene type linkage. Both
were measured in dichloromethane at RT.
J. Chem. Soc., Dalton Trans., 1994, 799.
Figure 58 Electronic spectra of Ru mononuclear [Ru(bipy)
2
(bsq)][PF
6
] (upper trace)
and Ru dinuclear [B(bipy)
2
(sq-sq)B(bipy)
2
]
2+
(lower trace) in CH
2
Cl
2
at the same
concentration.
N
N
Ir
N
N
Ir
O
O
O
O
N
N
Ir
O
O
175
J. Chem. Soc., Dalton Trans., 2000, 3162.
Figure 59 Electronic spectra of Os dinuclear complex [Os
2
(L
1
)]
n+
(n = 2, 3, or 4),
where L = bis-dioxolene bridging ligand, measured during a spectroelectrochemical
experiment in acetonitrile at –30°C. Spectra of n = 0 and n = 1 states could not be
recorded due to deposition of the reduced forms of the complex on the Pt electrode
surface.
176
Figure 60 The HOMO (left) and LUMO of iridium dinuclear complex in the trans-
configuration. The top image shows the optimized geometry in the trans form.
177

Figure 61 The HOMO (left) and LUMO of iridium dinuclear complex in the cis-
configuration. The optimized geometry for the cis isomer is shown above.
178
Figure 62 Experimental electronic spectra (visible to infrared region) and calculated
(TDDFT) transition energies of trans (olive) and cis (blue) isomers of the iridium
dinuclear complex. The experimental values were obtained in dichloromethane and
the calculations were done in gas phase. The absorbance is in units of M
-1
cm
-1
and
the oscillator strength is a dimensionless quantity that relates to the molar
absorbance.
179
Table 5 Data from electronic spectra and the electrochemical data of iridium
dinuclear complex and its mononuclear analog.
Sample Electronic spectra
a
λ
max
/nm (ε/10
-3
M
-1
cm
-1
)
Electrochemical potentials
(V vs. Fc
+
/Fc)
b
Ir mononuclear 267 (36.7), 313 (21.2), 408
(4.27), 594 (3.07)
-2.68, -0.88, +0.08
qr
,
+0.90
ir
Ir dinuclear 265 (117.3), 410 (15.0), 456
(14.2), 863 (31.8)
-2.92, -0.52, -0.16,
+0.80
qr
, +1.39
a: Dichloromethane solution, the molar absorption coefficients (ε) are given in
parentheses, measurements done at room temperature.
b: Cyclic voltammetry measured in acetonitrile, with 0.1M TBAP as supporting
electrolyte, at a scan rate of 100 mV/s, measured at room temperature. The potential
reported here is the average of anodic and cathodic peak potentials for a reversible
process, or the peak potential for an irreversible process. All potentials are reported
versus the ferrocenium/ferrocene (Fc
+
/Fc) couple. Unless otherwise noted, the redox
process is reversible.
180
Chapter 4 References
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181
20. McOmie J.F.W., Watts M.L., West D.E., Tetrahedron, 24(1968), 2289.
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182
Conclusion
The development of a combinatorial method for screening of metal catalysts led to a
study that uses two different outputs for analysis. A comparison of the two methods
shows that the visual output from LED is more sensitive than the thermal output
from heating of a resistor, both LED and resistor being in series with the
electrochemical cell.
The electrodes with metal particles supported on carbon paper were prepared by
thermal calcination and reduction. They appear as zero-valent metal nanoparticles on
the surface. Ninety-six different catalysts can be prepared at one time for
combinatorial screening.
The visual method for combinatorial screening of metal catalysts for the oxidation of
water works as a very sensitive technique. It is based on building a sensitive digital
ammeter to amplify current through the cell. This helps in the distinction of catalytic
activity of metals at the electrode. It is not just a sensitive method but also fast and
economical. We have shown that it works for noble metals in 8 x 2 array and when
used in 8 x 12 array the screening process would accelerate. The development of this
method leads to results that are in very close agreement with those obtained from
individual measurements from cells in the combinatorial setup. A difference in turn-
on potential of about 50mV between two metal catalysts is noticeable in the on/off of
LEDs in the circuit when the current density is 1mA/cm
2
. This combinatorial
183
screening method is like a direct measurement of 96 electrochemical cells in parallel,
yet qualitative in output of measurement and thereby fast. It should work as an
efficient method for screening of combinations of metals as well.
Novel cyclometalated complexes of iridium and platinum with dioxolene ligand
were synthesized and studied for their electronic and electrochemical properties. The
neutral complexes are open-shell molecules with unpaired electron largely centered
on the dioxolene ligand. Very intense, low-energy (in the red to near-infrared region)
transitions are observed from these complexes that exhibit rich redox chemistry.
Theoretical calculations provide the transition energies and give a good picture of the
orbitals involved in low-energy transitions. A possible internal relaxation seems
likely to deactivate the excited state faster than charge separation that makes these
materials very poor sensitizers in solar cells.
The above work was extended to study an iridium dinuclear complex with bis-
dioxolene bridging ligand. Changing the conformation of the redox-active bridging
ligand controls the metal-metal interactions in the dinuclear complex. The complex
is diamagnetic and exhibits strong electronic interaction between the two metal
centers through the bridging ligand. It shows very intense (ten times more than the
mononuclear analog) charge transfer transitions in the near-infrared region of
electromagnetic spectrum. Theoretical calculations suggest two isoenergetic forms of
the complex with the cis isomer being dominant over the trans isomer. Such neutral
184
iridium complexes should be investigated for applications in organic solar cells as
sensitizers.
185
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Appendices
Appendix A Matlab program for quantitative analysis.
% This program (GetIRdata) uses as input a serie of ASCII files (frames)
% and gives as an output a serie of TXT file with counts in pixels of
% interest
% COMMON = frame if you have files: frame100.txt to frame123.txt
clear, close all; % it's simple
%COMMON = input('Text name: ','s'); % asks for 1st part of file name
[fname,pname] = uigetfile('*.txt','Pick some image data file');
M = load([pname fname]);
NUM1 = input('Number of 1st frame: '); % asks for # of 1st file
NUM2 = input('Number of last frame: '); % asks for # of last file
NUMPIX = input('Number of pixels for averaging: ');
%NUMLAST = num2str(NUM2);
%LASTNAME = strcat(COMMON,NUMLAST,'.txt');
%M = dlmread(LASTNAME, '\t'); % read k-file
set(pcolor(M),'LineStyle','none');
colormap jet
shading faceted
195
colorbar
satisfied = 0;
while (~satisfied)
CLRMIN = input('Min of color axis (counts): ');
CLRMAX = input('Max of color axis (counts): ');
caxis ([CLRMIN CLRMAX]);
figure(gcf)
satisfied = input('Are these counts OK ? [0|1] ');
end
title('Click onto lower left and upper right corners for zoom')
[X, Y] = ginput(2);
axis([X(1) X(2) Y(1) Y(2)])
JR1 = round(X(1));
JR2 = round(X(2));
IR1 = round(Y(1));
IR2 = round(Y(2));
satisfied = 0;
while (~satisfied)
title('Click onto lower left, lower right and upper left resistors for grid')
[A, B] = ginput(3);
196
deltaX=round((A(2)-A(1))/22)-1;
deltaY=round((B(3)-B(1))/14)-1;
for p = 1:8
for q = 1:12
XINT(p,q)=round(A(1)+(q-1)*(A(2)-A(1))/11+(p-1)*(A(3)-A(1))/7);
YINT(p,q)=round(B(1)+(q-1)*(B(2)-B(1))/11+(p-1)*(B(3)-B(1))/7);
XMIN(p,q)=XINT(p,q)-deltaX;
YMIN(p,q)=YINT(p,q)-deltaY;
XMAX(p,q)=XINT(p,q)+deltaX;
YMAX(p,q)=YINT(p,q)+deltaY;
end
end
% Mark centers of resistors and ask for correction if necessary
figure(gcf)
hold on
for i = 1:8
for j = 1:12
rectangle('Position',[XINT(i,j)-1,YINT(i,j)-1,3,3]);
end
end
hold off
figure(gcf)
197
satisfied = input('Was the choice OK ? [0|1] ');
if (~satisfied)
set(pcolor(M),'LineStyle','none');
caxis ([CLRMIN CLRMAX]);
axis([X(1) X(2) Y(1) Y(2)])
end
end
set(pcolor(M),'LineStyle','none');
caxis ([CLRMIN CLRMAX]);
axis([X(1) X(2) Y(1) Y(2)])
colorbar
% Mark the big rectangles
figure(gcf)
hold on
for p = 1:8
for q = 1:12
rectangle('Position',[XMIN(p,q),YMIN(p,q),2*deltaX,2*deltaY]);
end
end
hold off
198
pause
for k = NUM1:NUM2
u = k + 1 - NUM1;
FULLNAME = [pname 'imag_ave_' num2str(k) '.txt'];
disp(['Processing file ' FULLNAME])
M = dlmread(FULLNAME, '\t'); % read k-file
for p = 1:8
for q = 1:12
V = M(YMIN(p,q):YMAX(p,q),XMIN(p,q):XMAX(p,q));
V = sort(V);
DINT(p,q) = mean(V(1:NUMPIX));
v = q + 12 * (p - 1);
DATA(u,v)=DINT(p,q);
end
end
disp(DATA(u,:))
end
dlmwrite([pname 'resist.txt'],DATA,'\t');
for i = 1:1:u
for j = 1:1:v
DATAN(i,j) = 10*(DATA(i,j)/DATA(1,j)-1);
199
end;
end;
dlmwrite([pname 'resistn.txt'],DATAN,'\t');
200
Appendix B Crystal data for tpy-Ir-sq.
Appendix B-1 Crystal data and structure refinement for tpy-Ir-sq.
Empirical formula C38 H40 Ir N2 O2
Formula weight 748.92
Temperature 143(2) K
Wavelength 0.71073 Å
Crystal system Triclinic
Space group P -1
Unit cell dimensions a = 10.4940(9) Å, a= 87.272(2)°.
b = 12.8533(12) Å, b= 77.782(2)°.
c = 12.9951(12) Å, g = 76.324(2)°.
Volume 1664.5(3) Å
3
Z 2
Density (calculated) 1.494 Mg/m
3
Absorption coefficient 4.045 mm
-1
F(000) 750
Crystal size 0.25 x 0.07 x 0.02 mm
3
Theta range for data collection 1.60 to 26.00°
Index ranges -8<=h<=12, -15<=k<=15, -14<=l<=16
Reflections collected 10199
Independent reflections 6343 [R(int) = 0.0265]
201
Completeness to theta = 26.00° 97.3 %
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.92 and 0.58
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 6343 / 0 / 396
Goodness-of-fit on F
2
1.005
Final R indices [I>2sigma(I)] R1 = 0.0341, wR2 = 0.0814
R indices (all data) R1 = 0.0401, wR2 = 0.0844
Largest diff. peak and hole 1.277 and -0.576 e.Å
-3
202
Appendix B-2 Atomic coordinates (x 10
4
) and equivalent isotropic displacement
parameters (Å
2
x 10
3
) for tpy-Ir-sq.
U(eq) is defined as one third of the trace of the orthogonalized U
ij
tensor.
____________________________________________________________________
x y z U(eq)
____________________________________________________________________
C(1) 6770(5) 7428(4) 3204(4) 26(1)
C(2) 8206(5) 7304(3) 3033(4) 23(1)
C(3) 8986(5) 7224(4) 1970(4) 26(1)
C(4) 8325(5) 7151(4) 1186(4) 28(1)
C(5) 6928(5) 7169(4) 1339(4) 32(1)
C(6) 6169(5) 7345(4) 2346(4) 30(1)
C(7) 10459(5) 7292(4) 1774(4) 34(1)
C(8) 10494(7) 8389(6) 2165(6) 65(2)
C(9) 11315(5) 6402(5) 2327(5) 48(2)
C(10) 11087(6) 7212(6) 587(4) 53(2)
C(11) 6357(6) 7012(5) 390(4) 43(1)
C(12) 6663(7) 7810(6) -472(5) 63(2)
C(13) 7006(8) 5872(6) -53(6) 70(2)
C(14) 4835(7) 7148(8) 673(5) 81(3)
C(15) 6849(5) 9829(4) 4631(4) 35(1)
C(16) 7027(6) 10851(4) 4580(5) 44(1)
203
C(17) 7849(7) 11114(5) 5169(6) 58(2)
C(18) 8500(7) 10334(4) 5779(5) 52(2)
C(19) 8293(6) 9305(4) 5806(4) 36(1)
C(20) 8914(6) 8403(4) 6398(4) 36(1)
C(21) 8566(5) 7434(4) 6273(3) 27(1)
C(22) 9169(5) 6547(4) 6803(4) 31(1)
C(23) 10073(5) 6600(4) 7440(4) 34(1)
C(24) 10360(6) 7589(5) 7554(5) 46(1)
C(25) 9795(6) 8475(4) 7032(5) 46(2)
C(26) 10730(6) 5629(5) 7981(5) 47(1)
C(27) 7759(6) 5156(4) 4883(4) 37(1)
C(28) 7413(6) 4174(4) 4951(5) 43(1)
C(29) 6294(6) 4053(5) 5661(5) 48(2)
C(30) 5559(5) 4894(4) 6308(4) 39(1)
C(31) 5917(5) 5870(4) 6231(4) 32(1)
C(32) 5236(5) 6831(4) 6844(4) 32(1)
C(33) 5792(5) 7739(4) 6558(4) 29(1)
C(34) 5182(5) 8690(4) 7147(4) 36(1)
C(35) 4070(6) 8770(5) 7954(4) 41(1)
C(36) 3543(6) 7873(5) 8187(4) 46(2)
C(37) 4110(6) 6918(5) 7659(4) 43(1)
C(38) 3442(7) 9804(5) 8553(5) 63(2)
Ir(1) 7291(1) 7516(1) 5312(1) 24(1)
204
N(1) 7479(4) 9056(3) 5220(3) 29(1)
N(2) 7020(4) 5996(3) 5499(3) 26(1)
O(1) 6070(3) 7615(3) 4152(2) 29(1)
O(2) 8727(3) 7271(3) 3853(2) 27(1)
____________________________________________________________________
205
Appendix B-3 Bond lengths [Å] and angles [°] for tpy-Ir-sq.
C(1)-O(1) 1.295(5)
C(1)-C(6) 1.411(7)
C(1)-C(2) 1.447(6)
C(2)-O(2) 1.291(5)
C(2)-C(3) 1.444(6)
C(3)-C(4) 1.367(7)
C(3)-C(7) 1.535(7)
C(4)-C(5) 1.433(7)
C(4)-H(4) 0.9500
C(5)-C(6) 1.378(7)
C(5)-C(11) 1.521(7)
C(6)-H(6) 0.9500
C(7)-C(9) 1.530(8)
C(7)-C(8) 1.533(8)
C(7)-C(10) 1.542(7)
C(8)-H(8A) 0.9800
C(8)-H(8B) 0.9800
C(8)-H(8C) 0.9800
C(9)-H(9A) 0.9800
C(9)-H(9B) 0.9800
C(9)-H(9C) 0.9800
206
C(10)-H(10A) 0.9800
C(10)-H(10B) 0.9800
C(10)-H(10C) 0.9800
C(11)-C(12) 1.518(9)
C(11)-C(14) 1.530(8)
C(11)-C(13) 1.544(9)
C(12)-H(12A) 0.9800
C(12)-H(12B) 0.9800
C(12)-H(12C) 0.9800
C(13)-H(13A) 0.9800
C(13)-H(13B) 0.9800
C(13)-H(13C) 0.9800
C(14)-H(14A) 0.9800
C(14)-H(14B) 0.9800
C(14)-H(14C) 0.9800
C(15)-N(1) 1.358(6)
C(15)-C(16) 1.366(7)
C(15)-H(15) 0.9500
C(16)-C(17) 1.373(9)
C(16)-H(16) 0.9500
C(17)-C(18) 1.389(8)
C(17)-H(17) 0.9500
C(18)-C(19) 1.388(7)
207
C(18)-H(18) 0.9500
C(19)-N(1) 1.356(6)
C(19)-C(20) 1.459(7)
C(20)-C(25) 1.383(8)
C(20)-C(21) 1.404(7)
C(21)-C(22) 1.394(7)
C(21)-Ir(1) 1.997(5)
C(22)-C(23) 1.399(7)
C(22)-H(22) 0.9500
C(23)-C(24) 1.396(7)
C(23)-C(26) 1.497(7)
C(24)-C(25) 1.373(8)
C(24)-H(24) 0.9500
C(25)-H(25) 0.9500
C(26)-H(26A) 0.9800
C(26)-H(26B) 0.9800
C(26)-H(26C) 0.9800
C(27)-N(2) 1.353(6)
C(27)-C(28) 1.388(7)
C(27)-H(27) 0.9500
C(28)-C(29) 1.367(8)
C(28)-H(28) 0.9500
C(29)-C(30) 1.374(8)
208
C(29)-H(29) 0.9500
C(30)-C(31) 1.385(7)
C(30)-H(30) 0.9500
C(31)-N(2) 1.371(6)
C(31)-C(32) 1.451(7)
C(32)-C(37) 1.397(7)
C(32)-C(33) 1.424(7)
C(33)-C(34) 1.415(7)
C(33)-Ir(1) 1.983(5)
C(34)-C(35) 1.381(8)
C(34)-H(34) 0.9500
C(35)-C(36) 1.387(9)
C(35)-C(38) 1.508(8)
C(36)-C(37) 1.375(8)
C(36)-H(36) 0.9500
C(37)-H(37) 0.9500
C(38)-H(38A) 0.9800
C(38)-H(38B) 0.9800
C(38)-H(38C) 0.9800
Ir(1)-N(1) 2.031(4)
Ir(1)-N(2) 2.035(4)
Ir(1)-O(2) 2.142(3)
Ir(1)-O(1) 2.157(3)
209
O(1)-C(1)-C(6) 121.8(4)
O(1)-C(1)-C(2) 118.3(4)
C(6)-C(1)-C(2) 119.9(4)
O(2)-C(2)-C(3) 123.1(4)
O(2)-C(2)-C(1) 117.6(4)
C(3)-C(2)-C(1) 119.3(4)
C(4)-C(3)-C(2) 116.6(4)
C(4)-C(3)-C(7) 123.8(4)
C(2)-C(3)-C(7) 119.4(4)
C(3)-C(4)-C(5) 125.1(4)
C(3)-C(4)-H(4) 117.4
C(5)-C(4)-H(4) 117.4
C(6)-C(5)-C(4) 117.6(4)
C(6)-C(5)-C(11) 123.6(5)
C(4)-C(5)-C(11) 118.8(4)
C(5)-C(6)-C(1) 120.9(4)
C(5)-C(6)-H(6) 119.5
C(1)-C(6)-H(6) 119.5
C(9)-C(7)-C(3) 112.8(4)
C(9)-C(7)-C(8) 110.0(5)
C(3)-C(7)-C(8) 107.7(5)
C(9)-C(7)-C(10) 107.6(5)
210
C(3)-C(7)-C(10) 110.6(4)
C(8)-C(7)-C(10) 108.1(5)
C(7)-C(8)-H(8A) 109.5
C(7)-C(8)-H(8B) 109.5
H(8A)-C(8)-H(8B) 109.5
C(7)-C(8)-H(8C) 109.5
H(8A)-C(8)-H(8C) 109.5
H(8B)-C(8)-H(8C) 109.5
C(7)-C(9)-H(9A) 109.5
C(7)-C(9)-H(9B) 109.5
H(9A)-C(9)-H(9B) 109.5
C(7)-C(9)-H(9C) 109.5
H(9A)-C(9)-H(9C) 109.5
H(9B)-C(9)-H(9C) 109.5
C(7)-C(10)-H(10A) 109.5
C(7)-C(10)-H(10B) 109.5
H(10A)-C(10)-H(10B) 109.5
C(7)-C(10)-H(10C) 109.5
H(10A)-C(10)-H(10C) 109.5
H(10B)-C(10)-H(10C) 109.5
C(12)-C(11)-C(5) 111.1(5)
C(12)-C(11)-C(14) 107.7(5)
C(5)-C(11)-C(14) 112.1(5)
211
C(12)-C(11)-C(13) 108.2(5)
C(5)-C(11)-C(13) 108.9(5)
C(14)-C(11)-C(13) 108.7(6)
C(11)-C(12)-H(12A) 109.5
C(11)-C(12)-H(12B) 109.5
H(12A)-C(12)-H(12B) 109.5
C(11)-C(12)-H(12C) 109.5
H(12A)-C(12)-H(12C) 109.5
H(12B)-C(12)-H(12C) 109.5
C(11)-C(13)-H(13A) 109.5
C(11)-C(13)-H(13B) 109.5
H(13A)-C(13)-H(13B) 109.5
C(11)-C(13)-H(13C) 109.5
H(13A)-C(13)-H(13C) 109.5
H(13B)-C(13)-H(13C) 109.5
C(11)-C(14)-H(14A) 109.5
C(11)-C(14)-H(14B) 109.5
H(14A)-C(14)-H(14B) 109.5
C(11)-C(14)-H(14C) 109.5
H(14A)-C(14)-H(14C) 109.5
H(14B)-C(14)-H(14C) 109.5
N(1)-C(15)-C(16) 122.6(5)
N(1)-C(15)-H(15) 118.7
212
C(16)-C(15)-H(15) 118.7
C(15)-C(16)-C(17) 118.7(5)
C(15)-C(16)-H(16) 120.6
C(17)-C(16)-H(16) 120.6
C(16)-C(17)-C(18) 119.5(5)
C(16)-C(17)-H(17) 120.3
C(18)-C(17)-H(17) 120.3
C(19)-C(18)-C(17) 119.9(6)
C(19)-C(18)-H(18) 120.1
C(17)-C(18)-H(18) 120.1
N(1)-C(19)-C(18) 120.0(5)
N(1)-C(19)-C(20) 113.8(4)
C(18)-C(19)-C(20) 126.1(5)
C(25)-C(20)-C(21) 121.4(5)
C(25)-C(20)-C(19) 123.5(5)
C(21)-C(20)-C(19) 115.1(5)
C(22)-C(21)-C(20) 116.8(5)
C(22)-C(21)-Ir(1) 128.8(4)
C(20)-C(21)-Ir(1) 114.5(4)
C(21)-C(22)-C(23) 122.8(5)
C(21)-C(22)-H(22) 118.6
C(23)-C(22)-H(22) 118.6
C(24)-C(23)-C(22) 118.0(5)
213
C(24)-C(23)-C(26) 120.4(5)
C(22)-C(23)-C(26) 121.6(5)
C(25)-C(24)-C(23) 120.6(5)
C(25)-C(24)-H(24) 119.7
C(23)-C(24)-H(24) 119.7
C(24)-C(25)-C(20) 120.4(5)
C(24)-C(25)-H(25) 119.8
C(20)-C(25)-H(25) 119.8
C(23)-C(26)-H(26A) 109.5
C(23)-C(26)-H(26B) 109.5
H(26A)-C(26)-H(26B) 109.5
C(23)-C(26)-H(26C) 109.5
H(26A)-C(26)-H(26C) 109.5
H(26B)-C(26)-H(26C) 109.5
N(2)-C(27)-C(28) 121.9(5)
N(2)-C(27)-H(27) 119.0
C(28)-C(27)-H(27) 119.0
C(29)-C(28)-C(27) 118.9(5)
C(29)-C(28)-H(28) 120.5
C(27)-C(28)-H(28) 120.5
C(28)-C(29)-C(30) 119.4(5)
C(28)-C(29)-H(29) 120.3
C(30)-C(29)-H(29) 120.3
214
C(29)-C(30)-C(31) 120.9(5)
C(29)-C(30)-H(30) 119.5
C(31)-C(30)-H(30) 119.5
N(2)-C(31)-C(30) 119.4(5)
N(2)-C(31)-C(32) 113.2(4)
C(30)-C(31)-C(32) 127.3(5)
C(37)-C(32)-C(33) 119.6(5)
C(37)-C(32)-C(31) 125.3(5)
C(33)-C(32)-C(31) 115.2(4)
C(34)-C(33)-C(32) 117.4(5)
C(34)-C(33)-Ir(1) 128.0(4)
C(32)-C(33)-Ir(1) 114.5(4)
C(35)-C(34)-C(33) 122.7(5)
C(35)-C(34)-H(34) 118.7
C(33)-C(34)-H(34) 118.7
C(34)-C(35)-C(36) 117.9(5)
C(34)-C(35)-C(38) 120.9(6)
C(36)-C(35)-C(38) 121.2(5)
C(37)-C(36)-C(35) 122.1(5)
C(37)-C(36)-H(36) 118.9
C(35)-C(36)-H(36) 118.9
C(36)-C(37)-C(32) 120.3(5)
C(36)-C(37)-H(37) 119.9
215
C(32)-C(37)-H(37) 119.9
C(35)-C(38)-H(38A) 109.5
C(35)-C(38)-H(38B) 109.5
H(38A)-C(38)-H(38B) 109.5
C(35)-C(38)-H(38C) 109.5
H(38A)-C(38)-H(38C) 109.5
H(38B)-C(38)-H(38C) 109.5
C(33)-Ir(1)-C(21) 89.01(19)
C(33)-Ir(1)-N(1) 95.72(18)
C(21)-Ir(1)-N(1) 80.56(18)
C(33)-Ir(1)-N(2) 80.56(18)
C(21)-Ir(1)-N(2) 98.59(17)
N(1)-Ir(1)-N(2) 176.21(15)
C(33)-Ir(1)-O(2) 172.87(16)
C(21)-Ir(1)-O(2) 98.09(16)
N(1)-Ir(1)-O(2) 86.06(14)
N(2)-Ir(1)-O(2) 97.71(14)
C(33)-Ir(1)-O(1) 96.34(16)
C(21)-Ir(1)-O(1) 174.52(15)
N(1)-Ir(1)-O(1) 97.72(15)
N(2)-Ir(1)-O(1) 83.47(14)
O(2)-Ir(1)-O(1) 76.56(12)
C(19)-N(1)-C(15) 119.2(4)
216
C(19)-N(1)-Ir(1) 116.0(3)
C(15)-N(1)-Ir(1) 124.8(4)
C(27)-N(2)-C(31) 119.3(4)
C(27)-N(2)-Ir(1) 124.5(3)
C(31)-N(2)-Ir(1) 115.8(3)
C(1)-O(1)-Ir(1) 113.0(3)
C(2)-O(2)-Ir(1) 114.1(3)
_____________________________________________________________
Symmetry transformations used to generate equivalent atoms:
Appendix B-4 Anisotropic displacement parameters (Å
2
x 10
3
) for tpy-Ir-sq.
The anisotropic displacement factor exponent takes the form: -2p
2
[h
2
a*
2
U
11
+ ...
+ 2 h k a* b* U
12
]
____________________________________________________________________
U
11
U
22
U
33
U
23
U
13
U
12
____________________________________________________________________
C(1) 24(2) 29(2) 23(2) 5(2) -5(2) -6(2)
C(2) 24(2) 24(2) 23(2) 3(2) -7(2) -9(2)
C(3) 29(3) 27(2) 20(2) 2(2) -3(2) -8(2)
C(4) 28(3) 38(3) 19(2) 4(2) -4(2) -9(2)
C(5) 31(3) 43(3) 24(2) 2(2) -8(2) -6(2)
C(6) 18(2) 40(3) 31(3) 7(2) -9(2) -4(2)
217
C(7) 29(3) 48(3) 25(3) 0(2) -1(2) -14(2)
C(8) 62(5) 78(5) 67(5) -7(4) 0(4) -49(4)
C(9) 25(3) 79(4) 37(3) 6(3) -7(2) -6(3)
C(10) 34(3) 100(5) 28(3) 7(3) -6(2) -25(3)
C(11) 33(3) 72(4) 24(3) -2(3) -8(2) -7(3)
C(12) 50(4) 110(6) 27(3) 10(3) -18(3) -8(4)
C(13) 73(5) 96(6) 51(4) -19(4) -29(4) -21(4)
C(14) 40(4) 181(9) 35(4) 1(5) -19(3) -39(5)
C(15) 35(3) 39(3) 29(3) 5(2) -10(2) -5(2)
C(16) 51(4) 33(3) 46(3) 9(2) -14(3) -5(3)
C(17) 84(5) 27(3) 68(5) 2(3) -30(4) -13(3)
C(18) 69(4) 40(3) 63(4) 7(3) -36(3) -23(3)
C(19) 47(3) 37(3) 31(3) 1(2) -20(2) -14(2)
C(20) 46(3) 33(3) 31(3) 0(2) -14(2) -9(2)
C(21) 28(3) 36(3) 17(2) 0(2) -3(2) -11(2)
C(22) 27(3) 36(3) 28(3) -1(2) -6(2) -5(2)
C(23) 28(3) 43(3) 31(3) 5(2) -10(2) -6(2)
C(24) 53(4) 49(3) 47(3) 2(3) -29(3) -18(3)
C(25) 64(4) 35(3) 53(4) 7(3) -30(3) -23(3)
C(26) 48(4) 53(3) 42(3) 7(3) -22(3) -8(3)
C(27) 45(3) 35(3) 30(3) 2(2) -6(2) -7(2)
C(28) 50(4) 34(3) 43(3) -1(2) -10(3) -7(3)
C(29) 56(4) 40(3) 54(4) 10(3) -17(3) -20(3)
218
C(30) 33(3) 52(3) 36(3) 15(3) -9(2) -17(3)
C(31) 29(3) 41(3) 28(3) 8(2) -10(2) -12(2)
C(32) 28(3) 44(3) 22(2) 5(2) -8(2) -5(2)
C(33) 31(3) 38(3) 18(2) 5(2) -10(2) -4(2)
C(34) 38(3) 40(3) 25(3) -1(2) -7(2) 2(2)
C(35) 36(3) 52(3) 25(3) 3(2) -6(2) 9(3)
C(36) 30(3) 75(4) 24(3) -3(3) 0(2) 1(3)
C(37) 35(3) 60(4) 33(3) 11(3) -7(2) -15(3)
C(38) 63(5) 65(4) 43(4) -10(3) 6(3) 6(4)
Ir(1) 25(1) 29(1) 18(1) 2(1) -5(1) -5(1)
N(1) 32(2) 29(2) 26(2) 1(2) -6(2) -5(2)
N(2) 28(2) 30(2) 24(2) 7(2) -11(2) -10(2)
O(1) 25(2) 36(2) 21(2) 2(1) -2(1) -5(2)
O(2) 22(2) 34(2) 24(2) 1(1) -6(1) -5(1)
____________________________________________________________________
219
Appendix B-5 Hydrogen coordinates (x 10
4
) and isotropic displacement parameters
(Å
2
x 10
3
) for tpy-Ir-sq.
____________________________________________________________________
x y z U(eq)
____________________________________________________________________
H(4) 8832 7083 484 34
H(6) 5228 7412 2464 36
H(8A) 9980 8954 1781 97
H(8B) 11424 8458 2044 97
H(8C) 10098 8458 2920 97
H(9A) 12224 6517 2226 72
H(9B) 11352 5707 2029 72
H(9C) 10918 6414 3082 72
H(10A) 10610 7814 219 79
H(10B) 11018 6537 309 79
H(10C) 12033 7236 479 79
H(12A) 6237 8538 -211 94
H(12B) 6316 7674 -1083 94
H(12C) 7635 7731 -677 94
H(13A) 7982 5775 -237 105
H(13B) 6674 5774 -684 105
220
H(13C) 6775 5344 479 105
H(14A) 4605 6666 1254 122
H(14B) 4520 6975 59 122
H(14C) 4406 7891 888 122
H(15) 6261 9653 4239 42
H(16) 6590 11370 4146 53
H(17) 7972 11823 5158 69
H(18) 9085 10505 6177 63
H(22) 8958 5879 6729 37
H(24) 10952 7650 7997 55
H(25) 10010 9141 7107 55
H(26A) 10749 4985 7598 70
H(26B) 10222 5602 8703 70
H(26C) 11648 5666 7996 70
H(27) 8536 5241 4391 44
H(28) 7946 3594 4511 52
H(29) 6025 3394 5706 57
H(30) 4795 4805 6814 47
H(34) 5553 9299 6981 43
H(36) 2766 7919 8729 55
H(37) 3733 6316 7850 51
H(38A) 4147 10149 8650 94
H(38B) 2927 9654 9243 94
221
H(38C) 2844 10281 8156 94
222
Appendix C Crystal data for dfppy-Pt-sq.
Appendix C-1 Crystal data and structure refinement for dfppy-Pt-sq.
Empirical formula C25 H26 F2 N O2 Pt
Formula weight 605.56
Temperature 193(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group C 2/m
Unit cell dimensions a = 28.4405(12) Å, a= 90°.
b = 6.8183(3) Å, b= 97.029(2)°.
c = 23.5381(11) Å, g = 90°.
Volume 4530.1(3) Å
3
Z 8
Density (calculated) 1.776 Mg/m
3
Absorption coefficient 6.232 mm
-1
F(000) 2360
Crystal size 0.43 x 0.04 x 0.01 mm
3
Theta range for data collection 1.74 to 25.74°
Index ranges -34<=h<=34, 0<=k<=8, 0<=l<=28
Reflections collected 8227
Independent reflections 8222 [R(int) = 0.0000]
223
Completeness to theta = 25.74° 99.7 %
Absorption correction Integration
Max. and min. transmission 0.9385 and 0.3733
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 8222 / 1418 / 724
Goodness-of-fit on F
2
0.901
Final R indices [I>2sigma(I)] R1 = 0.0441, wR2 = 0.0928
R indices (all data) R1 = 0.0925, wR2 = 0.1041
Largest diff. peak and hole 1.093 and -1.427 e.Å
-3
224
Appendix C-2 Atomic coordinates (x 10
4
) and equivalent isotropic displacement
parameters (Å
2
x 10
3
) for dfppy-Pt-sq.
U(eq) is defined as one third of the trace of the orthogonalized U
ij
tensor.
____________________________________________________________________
x y z U(eq)
____________________________________________________________________
Pt11 630(3) 5000 2706(2) 30(1)
O11 461(3) 5000 3498(3) 29(2)
O21 1317(3) 5000 3175(4) 30(2)
C11 815(4) 5000 3894(4) 26(2)
C21 1284(4) 5000 3719(4) 27(2)
C31 1687(4) 5000 4154(5) 26(2)
C41 1603(5) 5000 4712(5) 27(2)
C51 1142(5) 5000 4891(4) 23(2)
C61 755(4) 5000 4478(4) 25(2)
C71 2202(4) 5000 3992(7) 30(2)
C81 2573(5) 5000 4500(8) 35(3)
C91 2269(4) 3133(14) 3639(7) 58(3)
C111 1093(6) 5000 5538(4) 27(3)
C121 576(7) 5000 5666(6) 61(5)
C131 1342(7) 3199(13) 5817(4) 44(3)
F11 -1263(2) 5000 2516(3) 57(3)
F21 -553(3) 5000 815(3) 56(3)
225
C151 -20(4) 5000 2296(5) 29(2)
C161 -415(4) 5000 2577(5) 36(3)
C171 -856(4) 5000 2271(6) 41(3)
C181 -907(4) 5000 1684(6) 46(3)
C191 -508(4) 5000 1405(5) 41(2)
C201 -64(4) 5000 1710(5) 28(2)
C211 385(4) 5000 1474(5) 33(2)
C221 469(4) 5000 913(5) 48(3)
C231 923(5) 5000 778(5) 52(3)
C241 1301(4) 5000 1197(5) 49(3)
C251 1238(4) 5000 1764(5) 43(3)
N11 784(3) 5000 1913(4) 35(2)
Pt22 661(4) 0 2431(4) 32(1)
O12 546(4) 0 1588(4) 32(2)
O22 1373(4) 0 2225(5) 35(2)
C12 916(5) 0 1326(5) 30(2)
C22 1372(4) 0 1675(5) 34(2)
C32 1793(5) 0 1391(6) 31(2)
C42 1735(6) 0 809(6) 32(3)
C52 1289(6) 0 459(5) 32(3)
C62 886(6) 0 726(5) 32(2)
C72 2299(5) 0 1731(8) 51(3)
C82 2684(5) 0 1354(11) 62(5)
226
C92 2355(5) 1822(19) 2119(9) 92(5)
C112 1282(8) 0 -199(6) 42(4)
C122 778(9) 0 -521(7) 60(6)
C132 1537(9) 1827(17) -379(7) 53(5)
F12 -1226(3) 0 1923(4) 57(3)
F22 -613(3) 0 3864(4) 57(4)
C152 -4(5) 0 2595(6) 30(3)
C162 -381(5) 0 2172(6) 37(3)
C172 -833(5) 0 2312(7) 43(3)
C182 -917(5) 0 2875(7) 41(3)
C192 -535(5) 0 3297(6) 40(3)
C202 -80(5) 0 3159(6) 24(2)
C212 352(5) 0 3559(6) 30(3)
C222 404(6) 0 4146(6) 39(3)
C232 846(6) 0 4446(6) 44(3)
C242 1243(6) 0 4173(7) 47(3)
C252 1212(5) 0 3589(7) 39(3)
N12 770(4) 0 3273(5) 30(2)
Pt33 627(9) 5000 2744(6) 30(2)
O13 434(8) 5000 3592(8) 28(2)
O23 1260(8) 5000 3198(10) 29(2)
C13 805(10) 5000 3964(7) 26(2)
C23 1260(9) 5000 3749(9) 28(3)
227
C33 1683(10) 5000 4154(12) 26(3)
C43 1628(13) 5000 4720(11) 27(4)
C53 1182(14) 5000 4940(8) 22(3)
C63 777(12) 5000 4556(8) 24(3)
C73 2186(9) 5000 3955(18) 29(3)
C83 2577(11) 5000 4440(20) 34(5)
C93 2236(10) 3150(20) 3590(20) 59(5)
C113 1174(19) 5000 5596(8) 27(4)
C123 670(20) 5000 5771(12) 62(6)
C133 1430(20) 3180(20) 5851(11) 42(5)
F13 1778(6) 5000 1099(10) 66(8)
F23 140(7) 5000 524(7) 52(4)
C153 791(8) 5000 1951(8) 36(3)
C163 1249(8) 5000 1823(10) 43(4)
C173 1338(8) 5000 1265(10) 48(3)
C183 972(9) 5000 827(9) 52(3)
C193 513(8) 5000 958(7) 48(3)
C203 421(8) 5000 1518(7) 34(3)
C213 -44(8) 5000 1713(10) 27(3)
C223 -483(8) 5000 1396(12) 39(4)
C233 -883(8) 5000 1663(16) 44(3)
C243 -855(9) 5000 2246(16) 40(4)
C253 -428(10) 5000 2582(13) 35(4)
228
N13 -17(8) 5000 2325(9) 28(3)
Pt44 632(5) 0 2402(5) 31(1)
O14 511(5) 0 1490(5) 33(2)
O24 1294(5) 0 2208(6) 37(2)
C14 904(6) 0 1272(6) 32(2)
C24 1337(6) 0 1666(7) 37(3)
C34 1783(6) 0 1435(8) 33(3)
C44 1770(8) 0 856(9) 34(3)
C54 1348(9) 0 461(7) 32(3)
C64 921(8) 0 678(6) 33(3)
C74 2265(6) 0 1828(11) 50(4)
C84 2684(7) 0 1504(15) 61(4)
C94 2290(7) 1820(20) 2216(12) 91(6)
C114 1390(11) 0 -188(8) 40(4)
C124 908(12) 0 -560(8) 51(5)
C134 1666(12) 1810(20) -337(9) 54(5)
F14 1611(4) 0 4513(5) 57(4)
F24 -44(4) 0 4376(5) 67(5)
C154 726(6) 0 3253(6) 30(3)
C164 1163(6) 0 3574(7) 35(3)
C174 1198(6) 0 4159(7) 43(3)
C184 798(7) 0 4433(7) 42(3)
C194 361(6) 0 4109(6) 40(3)
229
C204 325(6) 0 3521(6) 30(3)
C214 -116(6) 0 3138(7) 26(3)
C224 -573(6) 0 3269(9) 41(3)
C234 -945(6) 0 2842(11) 41(3)
C244 -867(6) 0 2280(10) 45(3)
C254 -419(7) 0 2127(8) 38(3)
N14 -36(5) 0 2548(6) 33(2)
____________________________________________________________________
230
Appendix C-3 Bond lengths [Å] and angles [°] for dfppy-Pt-sq.
Pt11-N11 1.969(10)
Pt11-C151 1.976(10)
Pt11-O11 1.981(8)
Pt11-O21 2.123(8)
O11-C11 1.285(7)
O21-C21 1.296(7)
C11-C61 1.406(7)
C11-C21 1.444(7)
C21-C31 1.440(7)
C31-C41 1.362(7)
C31-C71 1.560(9)
C41-C51 1.428(7)
C41-H41 0.9300
C51-C61 1.376(7)
C51-C111 1.547(9)
C61-H61 0.9300
C71-C81 1.492(9)
C71-C91 1.544(7)
C71-C91#1 1.544(7)
C81-H8A1 0.9600
C81-H8B1 0.9600
231
C81-H8C1 0.9600
C91-H9A1 0.9600
C91-H9B1 0.9600
C91-H9C1 0.9600
C111-C131#1 1.525(7)
C111-C131 1.525(7)
C111-C121 1.536(10)
C121-H12A1 0.9600
C121-H12B1 0.9600
C121-H12C1 0.9600
C131-H13A1 0.9600
C131-H13B1 0.9600
C131-H13C1 0.9600
F11-C171 1.354(12)
F21-C191 1.380(13)
C151-C161 1.372(7)
C151-C201 1.370(6)
C161-C171 1.368(6)
C161-H161 0.9300
C171-C181 1.373(6)
C181-C191 1.379(6)
C181-H181 0.9300
C191-C201 1.375(6)
232
C201-C211 1.454(9)
C211-C221 1.371(6)
C211-N11 1.437(10)
C221-C231 1.367(6)
C221-H221 0.9300
C231-C241 1.365(6)
C231-H231 0.9300
C241-C251 1.368(6)
C241-H241 0.9300
C251-N11 1.380(10)
C251-H251 0.9300
Pt22-N12 1.968(12)
Pt22-O12 1.971(9)
Pt22-C152 1.976(11)
Pt22-O22 2.140(9)
O12-C12 1.285(7)
O22-C22 1.295(7)
C12-C62 1.405(8)
C12-C22 1.448(8)
C22-C32 1.440(8)
C32-C42 1.360(8)
C32-C72 1.558(9)
C42-C52 1.426(8)
233
C42-H42 0.9300
C52-C62 1.373(8)
C52-C112 1.547(9)
C62-H62 0.9300
C72-C82 1.492(10)
C72-C92 1.538(7)
C72-C92#2 1.538(7)
C82-H8A2 0.9600
C82-H8B2 0.9600
C82-H8C2 0.9600
C92-H9A2 0.9600
C92-H9B2 0.9600
C92-H9C2 0.9600
C112-C132#2 1.527(7)
C112-C132 1.527(7)
C112-C122 1.536(11)
C122-H12A2 0.9600
C122-H12B2 0.9600
C122-H12C2 0.9600
C132-H13A2 0.9600
C132-H13B2 0.9600
C132-H13C2 0.9600
F12-C172 1.354(12)
234
F22-C192 1.378(13)
C152-C162 1.371(8)
C152-C202 1.370(8)
C162-C172 1.366(7)
C162-H162 0.9300
C172-C182 1.374(7)
C182-C192 1.380(7)
C182-H182 0.9300
C192-C202 1.375(7)
C202-C212 1.452(9)
C212-C222 1.373(7)
C212-N12 1.435(11)
C222-C232 1.365(7)
C222-H222 0.9300
C232-C242 1.365(7)
C232-H232 0.9300
C242-C252 1.367(7)
C242-H242 0.9300
C252-N12 1.379(11)
C252-H252 0.9300
Pt33-N13 1.970(13)
Pt33-C153 1.979(13)
Pt33-O23 1.980(11)
235
Pt33-O13 2.134(11)
O13-C13 1.285(8)
O23-C23 1.296(7)
C13-C63 1.406(8)
C13-C23 1.447(8)
C23-C33 1.440(8)
C33-C43 1.360(8)
C33-C73 1.559(9)
C43-C53 1.428(8)
C43-H43 0.9300
C53-C63 1.374(8)
C53-C113 1.547(10)
C63-H63 0.9300
C73-C83 1.492(10)
C73-C93 1.542(8)
C73-C93#1 1.542(8)
C83-H8A3 0.9600
C83-H8B3 0.9600
C83-H8C3 0.9600
C93-H9A3 0.9600
C93-H9B3 0.9600
C93-H9C3 0.9600
C113-C133#1 1.526(8)
236
C113-C133 1.527(8)
C113-C123 1.536(11)
C123-H12A3 0.9600
C123-H12B3 0.9600
C123-H12C3 0.9600
C133-H13A3 0.9600
C133-H13B3 0.9600
C133-H13C3 0.9600
F13-C173 1.355(13)
F23-C193 1.379(13)
C153-C163 1.372(8)
C153-C203 1.371(8)
C163-C173 1.367(7)
C163-H163 0.9300
C173-C183 1.374(7)
C183-C193 1.378(7)
C183-H183 0.9300
C193-C203 1.374(7)
C203-C213 1.453(9)
C213-C223 1.372(7)
C213-N13 1.435(11)
C223-C233 1.367(8)
C223-H223 0.9300
237
C233-C243 1.365(8)
C233-H233 0.9300
C243-C253 1.367(8)
C243-H243 0.9300
C253-N13 1.380(11)
C253-H253 0.9300
Pt44-N14 1.972(13)
Pt44-C154 1.987(13)
Pt44-O24 1.992(10)
Pt44-O14 2.133(10)
O14-C14 1.285(7)
O24-C24 1.295(7)
C14-C64 1.405(8)
C14-C24 1.448(8)
C24-C34 1.440(8)
C34-C44 1.360(8)
C34-C74 1.558(9)
C44-C54 1.427(8)
C44-H44 0.9300
C54-C64 1.373(8)
C54-C114 1.547(9)
C64-H64 0.9300
C74-C84 1.491(10)
238
C74-C94 1.539(7)
C74-C94#2 1.539(7)
C84-H8A4 0.9600
C84-H8B4 0.9600
C84-H8C4 0.9600
C94-H9A4 0.9600
C94-H9B4 0.9600
C94-H9C4 0.9600
C114-C134 1.526(7)
C114-C134#2 1.526(7)
C114-C124 1.536(11)
C124-H12A4 0.9600
C124-H12B4 0.9600
C124-H12C4 0.9600
C134-H13A4 0.9600
C134-H13B4 0.9600
C134-H13C4 0.9600
F14-C174 1.355(13)
F24-C194 1.378(13)
C154-C204 1.370(8)
C154-C164 1.374(8)
C164-C174 1.366(7)
C164-H164 0.9300
239
C174-C184 1.374(7)
C184-C194 1.376(7)
C184-H184 0.9300
C194-C204 1.375(7)
C204-C214 1.452(9)
C214-C224 1.372(7)
C214-N14 1.434(11)
C224-C234 1.368(8)
C224-H224 0.9300
C234-C244 1.366(8)
C234-H234 0.9300
C244-C254 1.366(8)
C244-H244 0.9300
C254-N14 1.380(11)
C254-H254 0.9300
N11-Pt11-C151 80.8(3)
N11-Pt11-O11 178.9(4)
C151-Pt11-O11 98.1(4)
N11-Pt11-O21 101.3(4)
C151-Pt11-O21 177.9(4)
O11-Pt11-O21 79.8(2)
C11-O11-Pt11 115.2(5)
240
C21-O21-Pt11 110.0(5)
O11-C11-C61 122.1(6)
O11-C11-C21 117.5(6)
C61-C11-C21 120.4(5)
O21-C21-C31 123.9(6)
O21-C21-C11 117.5(6)
C31-C21-C11 118.6(6)
C41-C31-C21 117.9(5)
C41-C31-C71 121.0(6)
C21-C31-C71 121.0(6)
C31-C41-C51 124.0(6)
C31-C41-H41 118.0
C51-C41-H41 118.0
C61-C51-C41 118.4(6)
C61-C51-C111 122.4(6)
C41-C51-C111 119.2(6)
C51-C61-C11 120.6(6)
C51-C61-H61 119.7
C11-C61-H61 119.7
C81-C71-C91 108.0(5)
C81-C71-C91#1 108.0(5)
C91-C71-C91#1 111.1(11)
C81-C71-C31 113.3(7)
241
C91-C71-C31 108.2(5)
C91#1-C71-C31 108.2(5)
C71-C81-H8A1 109.5
C71-C81-H8B1 109.5
H8A1-C81-H8B1 109.5
C71-C81-H8C1 109.5
H8A1-C81-H8C1 109.5
H8B1-C81-H8C1 109.5
C71-C91-H9A1 109.5
C71-C91-H9B1 109.5
H9A1-C91-H9B1 109.5
C71-C91-H9C1 109.5
H9A1-C91-H9C1 109.5
H9B1-C91-H9C1 109.5
C131#1-C111-C131 107.2(10)
C131#1-C111-C121 108.8(5)
C131-C111-C121 108.8(5)
C131#1-C111-C51 109.3(5)
C131-C111-C51 109.3(5)
C121-C111-C51 113.3(7)
C111-C121-H12A1 109.5
C111-C121-H12B1 109.5
H12A1-C121-H12B1 109.5
242
C111-C121-H12C1 109.5
H12A1-C121-H12C1 109.5
H12B1-C121-H12C1 109.5
C111-C131-H13A1 109.5
C111-C131-H13B1 109.5
H13A1-C131-H13B1 109.5
C111-C131-H13C1 109.5
H13A1-C131-H13C1 109.5
H13B1-C131-H13C1 109.5
C161-C151-C201 120.4(7)
C161-C151-Pt11 122.4(7)
C201-C151-Pt11 117.2(6)
C171-C161-C151 119.9(7)
C171-C161-H161 120.0
C151-C161-H161 120.0
F11-C171-C161 123.5(10)
F11-C171-C181 115.9(10)
C161-C171-C181 120.5(7)
C171-C181-C191 119.1(7)
C171-C181-H181 120.4
C191-C181-H181 120.4
C201-C191-F21 119.5(9)
C201-C191-C181 120.6(7)
243
F21-C191-C181 119.9(9)
C191-C201-C151 119.4(7)
C191-C201-C211 126.4(10)
C151-C201-C211 114.1(10)
C221-C211-N11 118.5(8)
C221-C211-C201 129.3(11)
N11-C211-C201 112.2(10)
C231-C221-C211 120.3(8)
C231-C221-H221 119.8
C211-C221-H221 119.9
C241-C231-C221 121.0(7)
C241-C231-H231 119.5
C221-C231-H231 119.5
C231-C241-C251 121.2(8)
C231-C241-H241 119.4
C251-C241-H241 119.4
C241-C251-N11 119.1(9)
C241-C251-H251 120.4
N11-C251-H251 120.4
C251-N11-C211 119.9(9)
C251-N11-Pt11 124.4(7)
C211-N11-Pt11 115.7(7)
N12-Pt22-O12 179.5(5)
244
N12-Pt22-C152 80.8(3)
O12-Pt22-C152 98.7(6)
N12-Pt22-O22 101.0(5)
O12-Pt22-O22 79.4(3)
C152-Pt22-O22 178.1(6)
C12-O12-Pt22 116.0(6)
C22-O22-Pt22 110.0(5)
O12-C12-C62 122.0(7)
O12-C12-C22 117.3(6)
C62-C12-C22 120.7(6)
O22-C22-C32 124.4(6)
O22-C22-C12 117.3(6)
C32-C22-C12 118.4(6)
C42-C32-C22 117.5(6)
C42-C32-C72 120.5(7)
C22-C32-C72 122.0(7)
C32-C42-C52 124.9(7)
C32-C42-H42 117.6
C52-C42-H42 117.6
C62-C52-C42 118.0(6)
C62-C52-C112 123.3(7)
C42-C52-C112 118.7(7)
C52-C62-C12 120.6(7)
245
C52-C62-H62 119.7
C12-C62-H62 119.7
C82-C72-C92 108.8(6)
C82-C72-C92#2 108.8(6)
C92-C72-C92#2 107.7(14)
C82-C72-C32 113.3(8)
C92-C72-C32 109.1(5)
C92#2-C72-C32 109.1(5)
C72-C82-H8A2 109.5
C72-C82-H8B2 109.5
H8A2-C82-H8B2 109.5
C72-C82-H8C2 109.5
H8A2-C82-H8C2 109.5
H8B2-C82-H8C2 109.5
C72-C92-H9A2 109.5
C72-C92-H9B2 109.5
H9A2-C92-H9B2 109.5
C72-C92-H9C2 109.5
H9A2-C92-H9C2 109.5
H9B2-C92-H9C2 109.5
C132#2-C112-C132 109.4(14)
C132#2-C112-C122 108.0(6)
C132-C112-C122 108.0(6)
246
C132#2-C112-C52 109.2(6)
C132-C112-C52 109.2(6)
C122-C112-C52 113.0(8)
C112-C122-H12A2 109.5
C112-C122-H12B2 109.5
H12A2-C122-H12B2 109.5
C112-C122-H12C2 109.5
H12A2-C122-H12C2 109.5
H12B2-C122-H12C2 109.5
C112-C132-H13A2 109.5
C112-C132-H13B2 109.5
H13A2-C132-H13B2 109.5
C112-C132-H13C2 109.5
H13A2-C132-H13C2 109.5
H13B2-C132-H13C2 109.5
C162-C152-C202 120.2(8)
C162-C152-Pt22 122.7(8)
C202-C152-Pt22 117.1(7)
C172-C162-C152 120.0(9)
C172-C162-H162 120.0
C152-C162-H162 120.0
F12-C172-C162 124.0(11)
F12-C172-C182 115.2(11)
247
C162-C172-C182 120.8(8)
C172-C182-C192 118.7(8)
C172-C182-H182 120.7
C192-C182-H182 120.7
F22-C192-C202 119.8(10)
F22-C192-C182 119.4(10)
C202-C192-C182 120.8(8)
C192-C202-C152 119.5(8)
C192-C202-C212 126.4(11)
C152-C202-C212 114.1(10)
C222-C212-N12 118.5(9)
C222-C212-C202 129.2(12)
N12-C212-C202 112.3(11)
C232-C222-C212 120.0(9)
C232-C222-H222 120.0
C212-C222-H222 120.0
C242-C232-C222 121.3(9)
C242-C232-H232 119.4
C222-C232-H232 119.4
C232-C242-C252 121.2(9)
C232-C242-H242 119.4
C252-C242-H242 119.4
C242-C252-N12 119.0(10)
248
C242-C252-H252 120.5
N12-C252-H252 120.5
C252-N12-C212 120.0(10)
C252-N12-Pt22 124.3(8)
C212-N12-Pt22 115.7(7)
N13-Pt33-C153 80.8(4)
N13-Pt33-O23 177.3(10)
C153-Pt33-O23 101.9(10)
N13-Pt33-O13 97.9(10)
C153-Pt33-O13 178.8(10)
O23-Pt33-O13 79.4(4)
C13-O13-Pt33 110.7(6)
C23-O23-Pt33 115.4(6)
O13-C13-C63 122.3(7)
O13-C13-C23 117.2(7)
C63-C13-C23 120.5(7)
O23-C23-C33 124.1(7)
O23-C23-C13 117.3(7)
C33-C23-C13 118.6(7)
C43-C33-C23 117.5(7)
C43-C33-C73 121.0(7)
C23-C33-C73 121.5(7)
C33-C43-C53 124.7(7)
249
C33-C43-H43 117.7
C53-C43-H43 117.7
C63-C53-C43 118.2(7)
C63-C53-C113 122.9(8)
C43-C53-C113 118.9(7)
C53-C63-C13 120.5(7)
C53-C63-H63 119.7
C13-C63-H63 119.7
C83-C73-C93 108.3(7)
C83-C73-C93#1 108.3(7)
C93-C73-C93#1 109.7(19)
C83-C73-C33 113.4(8)
C93-C73-C33 108.6(7)
C93#1-C73-C33 108.6(6)
C73-C83-H8A3 109.5
C73-C83-H8B3 109.5
H8A3-C83-H8B3 109.5
C73-C83-H8C3 109.5
H8A3-C83-H8C3 109.5
H8B3-C83-H8C3 109.5
C73-C93-H9A3 109.5
C73-C93-H9B3 109.5
H9A3-C93-H9B3 109.5
250
C73-C93-H9C3 109.5
H9A3-C93-H9C3 109.5
H9B3-C93-H9C3 109.5
C133#1-C113-C133 109(2)
C133#1-C113-C123 108.2(7)
C133-C113-C123 108.2(7)
C133#1-C113-C53 109.1(7)
C133-C113-C53 109.1(7)
C123-C113-C53 113.3(9)
C113-C123-H12A3 109.5
C113-C123-H12B3 109.5
H12A3-C123-H12B3 109.5
C113-C123-H12C3 109.5
H12A3-C123-H12C3 109.5
H12B3-C123-H12C3 109.5
C113-C133-H13A3 109.5
C113-C133-H13B3 109.5
H13A3-C133-H13B3 109.5
C113-C133-H13C3 109.5
H13A3-C133-H13C3 109.5
H13B3-C133-H13C3 109.5
C163-C153-C203 120.0(9)
C163-C153-Pt33 123.1(9)
251
C203-C153-Pt33 116.9(8)
C173-C163-C153 120.1(9)
C173-C163-H163 119.9
C153-C163-H163 119.9
F13-C173-C163 124.2(12)
F13-C173-C183 115.1(11)
C163-C173-C183 120.6(8)
C173-C183-C193 118.9(9)
C173-C183-H183 120.5
C193-C183-H183 120.5
C203-C193-F23 119.6(10)
C203-C193-C183 120.7(8)
F23-C193-C183 119.8(10)
C193-C203-C153 119.6(8)
C193-C203-C213 126.0(12)
C153-C203-C213 114.3(11)
C223-C213-N13 118.6(9)
C223-C213-C203 129.2(12)
N13-C213-C203 112.2(11)
C233-C223-C213 120.3(9)
C233-C223-H223 119.8
C213-C223-H223 119.8
C243-C233-C223 120.8(9)
252
C243-C233-H233 119.6
C223-C233-H233 119.6
C233-C243-C253 121.3(10)
C233-C243-H243 119.3
C253-C243-H243 119.3
C243-C253-N13 119.2(10)
C243-C253-H253 120.4
N13-C253-H253 120.4
C253-N13-C213 119.8(10)
C253-N13-Pt33 124.5(10)
C213-N13-Pt33 115.8(8)
N14-Pt44-C154 80.7(4)
N14-Pt44-O24 176.7(7)
C154-Pt44-O24 102.6(7)
N14-Pt44-O14 97.8(7)
C154-Pt44-O14 178.5(7)
O24-Pt44-O14 79.0(3)
C14-O14-Pt44 111.2(6)
C24-O24-Pt44 115.6(6)
O14-C14-C64 122.3(7)
O14-C14-C24 117.1(7)
C64-C14-C24 120.6(6)
O24-C24-C34 124.4(7)
253
O24-C24-C14 117.2(6)
C34-C24-C14 118.4(6)
C44-C34-C24 117.6(6)
C44-C34-C74 120.5(7)
C24-C34-C74 121.9(7)
C34-C44-C54 124.8(7)
C34-C44-H44 117.6
C54-C44-H44 117.6
C64-C54-C44 118.0(7)
C64-C54-C114 123.1(7)
C44-C54-C114 118.8(7)
C54-C64-C14 120.6(7)
C54-C64-H64 119.7
C14-C64-H64 119.7
C84-C74-C94 108.7(6)
C84-C74-C94#2 108.7(6)
C94-C74-C94#2 107.8(17)
C84-C74-C34 113.5(8)
C94-C74-C34 109.0(6)
C94#2-C74-C34 109.0(6)
C74-C84-H8A4 109.5
C74-C84-H8B4 109.5
H8A4-C84-H8B4 109.5
254
C74-C84-H8C4 109.5
H8A4-C84-H8C4 109.5
H8B4-C84-H8C4 109.5
C74-C94-H9A4 109.5
C74-C94-H9B4 109.5
H9A4-C94-H9B4 109.5
C74-C94-H9C4 109.5
H9A4-C94-H9C4 109.5
H9B4-C94-H9C4 109.5
C134-C114-C134#2 108.0(17)
C134-C114-C124 108.5(7)
C134#2-C114-C124 108.5(7)
C134-C114-C54 109.4(6)
C134#2-C114-C54 109.4(6)
C124-C114-C54 113.0(8)
C114-C124-H12A4 109.5
C114-C124-H12B4 109.5
H12A4-C124-H12B4 109.5
C114-C124-H12C4 109.5
H12A4-C124-H12C4 109.5
H12B4-C124-H12C4 109.5
C114-C134-H13A4 109.5
C114-C134-H13B4 109.5
255
H13A4-C134-H13B4 109.5
C114-C134-H13C4 109.5
H13A4-C134-H13C4 109.5
H13B4-C134-H13C4 109.5
C204-C154-C164 119.6(9)
C204-C154-Pt44 116.6(8)
C164-C154-Pt44 123.7(9)
C174-C164-C154 120.2(9)
C174-C164-H164 119.9
C154-C164-H164 119.9
F14-C174-C164 124.7(11)
F14-C174-C184 114.6(11)
C164-C174-C184 120.7(8)
C194-C184-C174 118.9(8)
C194-C184-H184 120.6
C174-C184-H184 120.5
F24-C194-C204 119.6(10)
F24-C194-C184 119.8(10)
C204-C194-C184 120.6(8)
C194-C204-C154 119.9(8)
C194-C204-C214 125.4(12)
C154-C204-C214 114.7(11)
C224-C214-N14 119.0(9)
256
C224-C214-C204 129.0(12)
N14-C214-C204 112.1(11)
C234-C224-C214 120.2(9)
C234-C224-H224 119.9
C214-C224-H224 119.9
C244-C234-C224 120.6(9)
C244-C234-H234 119.7
C224-C234-H234 119.7
C254-C244-C234 121.5(10)
C254-C244-H244 119.2
C234-C244-H244 119.2
C244-C254-N14 119.3(10)
C244-C254-H254 120.4
N14-C254-H254 120.4
C254-N14-C214 119.4(10)
C254-N14-Pt44 124.6(9)
C214-N14-Pt44 116.0(8)
_____________________________________________________________
Symmetry transformations used to generate equivalent atoms:
#1 x,-y+1,z #2 x,-y,z
257
Appendix C-4 Anisotropic displacement parameters (Å
2
x 10
3
) for dfppy-Pt-sq.
The anisotropic displacement factor exponent takes the form: -2p
2
[h
2
a*
2
U
11
+ ...
+ 2 h k a* b* U
12
]
____________________________________________________________________
U
11
U
22
U
33
U
23
U
13
U
12
____________________________________________________________________
Pt11 25(1) 30(2) 34(1) 0 1(1) 0
O11 19(2) 32(5) 36(2) 0 2(2) 0
O21 22(2) 33(5) 34(2) 0 4(2) 0
C11 19(2) 26(5) 35(2) 0 3(2) 0
C21 19(2) 28(5) 34(2) 0 3(2) 0
C31 19(2) 22(6) 37(2) 0 2(2) 0
C41 17(3) 27(7) 36(2) 0 0(3) 0
C51 18(4) 14(5) 36(2) 0 1(2) 0
C61 16(3) 24(6) 36(2) 0 3(3) 0
C71 20(3) 30(5) 40(5) 0 4(3) 0
C81 18(3) 44(8) 42(7) 0 4(4) 0
C91 29(5) 70(7) 77(7) -40(5) 8(5) 5(5)
C111 15(7) 28(5) 37(2) 0 1(3) 0
C121 18(9) 116(13) 50(8) 0 7(7) 0
C131 48(9) 39(5) 42(5) 11(4) -4(5) 4(4)
F11 28(2) 82(7) 58(5) 0 2(3) 0
258
F21 48(6) 77(7) 40(3) 0 -10(3) 0
C151 28(2) 21(6) 36(2) 0 -2(2) 0
C161 28(2) 39(8) 39(4) 0 -1(2) 0
C171 27(2) 48(8) 48(4) 0 -2(3) 0
C181 32(3) 56(8) 47(4) 0 -8(3) 0
C191 37(3) 44(7) 39(3) 0 -6(2) 0
C201 33(2) 14(6) 36(2) 0 -3(2) 0
C211 38(3) 27(7) 34(2) 0 0(2) 0
C221 50(4) 59(8) 35(2) 0 3(3) 0
C231 56(5) 63(8) 38(4) 0 11(3) 0
C241 47(4) 58(7) 44(4) 0 13(3) 0
C251 36(3) 52(8) 41(4) 0 9(3) 0
N11 33(2) 37(6) 36(2) 0 3(2) 0
Pt22 29(2) 35(2) 33(1) 0 10(2) 0
O12 26(3) 36(5) 34(2) 0 8(2) 0
O22 27(2) 41(6) 38(3) 0 7(2) 0
C12 28(3) 29(6) 35(2) 0 9(2) 0
C22 27(3) 39(7) 39(3) 0 9(2) 0
C32 28(3) 26(6) 41(3) 0 11(2) 0
C42 32(4) 27(7) 41(3) 0 12(3) 0
C52 32(5) 28(6) 39(3) 0 12(2) 0
C62 31(4) 30(7) 36(2) 0 10(3) 0
C72 27(3) 85(7) 43(7) 0 12(3) 0
259
C82 30(4) 108(11) 52(12) 0 18(6) 0
C92 40(8) 155(11) 79(10) -61(7) 3(6) -14(7)
C112 29(10) 59(6) 40(3) 0 13(3) 0
C122 33(13) 102(11) 45(6) 0 7(6) 0
C132 50(13) 67(7) 43(6) 15(5) 12(7) -4(6)
F12 33(3) 71(8) 63(5) 0 -6(4) 0
F22 54(7) 78(10) 45(4) 0 27(4) 0
C152 28(2) 34(8) 29(3) 0 6(2) 0
C162 31(2) 46(7) 33(3) 0 3(3) 0
C172 29(2) 54(9) 46(4) 0 3(3) 0
C182 29(3) 45(7) 52(4) 0 13(3) 0
C192 34(3) 49(8) 40(4) 0 15(2) 0
C202 31(3) 11(7) 31(3) 0 9(2) 0
C212 37(3) 25(8) 28(2) 0 6(2) 0
C222 61(5) 30(7) 27(2) 0 6(3) 0
C232 71(6) 32(7) 28(4) 0 -5(3) 0
C242 57(5) 38(7) 42(3) 0 -11(4) 0
C252 35(3) 37(8) 43(3) 0 -3(3) 0
N12 30(3) 25(6) 34(2) 0 3(2) 0
Pt33 26(3) 28(5) 35(2) 0 0(2) 0
O13 19(3) 28(6) 35(2) 0 0(2) 0
O23 22(3) 30(6) 36(3) 0 3(2) 0
C13 18(3) 25(6) 35(2) 0 1(3) 0
260
C23 19(3) 28(8) 36(3) 0 2(2) 0
C33 18(3) 22(9) 38(3) 0 2(3) 0
C43 17(4) 26(10) 37(3) 0 1(4) 0
C53 17(5) 11(9) 36(3) 0 1(3) 0
C63 17(4) 19(7) 35(2) 0 1(3) 0
C73 19(3) 29(7) 39(7) 0 3(4) 0
C83 18(4) 45(10) 40(9) 0 4(7) 0
C93 30(8) 70(9) 77(9) -41(7) 7(7) 5(8)
C113 13(9) 30(7) 37(3) 0 0(4) 0
C123 19(11) 115(14) 53(10) 0 12(9) 0
C133 47(11) 35(8) 42(7) 10(6) -7(8) 3(7)
F13 50(5) 80(20) 73(12) 0 30(6) 0
F23 58(6) 67(11) 32(4) 0 5(5) 0
C153 32(3) 39(10) 37(2) 0 4(2) 0
C163 34(3) 51(11) 44(4) 0 8(3) 0
C173 44(4) 55(8) 48(5) 0 16(3) 0
C183 55(5) 62(9) 40(4) 0 14(4) 0
C193 49(4) 60(9) 36(2) 0 6(3) 0
C203 37(3) 32(8) 34(2) 0 2(2) 0
C213 33(3) 14(9) 34(3) 0 -2(2) 0
C223 37(4) 42(10) 36(4) 0 -6(3) 0
C233 32(3) 51(8) 45(5) 0 -7(4) 0
C243 27(3) 47(11) 46(5) 0 -1(4) 0
261
C253 27(3) 39(10) 39(4) 0 0(3) 0
N13 27(3) 22(9) 35(3) 0 -1(2) 0
Pt44 26(2) 33(3) 33(1) 0 -1(1) 0
O14 31(3) 34(6) 34(2) 0 5(2) 0
O24 29(2) 42(7) 40(3) 0 5(2) 0
C14 31(3) 28(6) 38(2) 0 7(2) 0
C24 30(3) 40(7) 42(3) 0 6(2) 0
C34 31(3) 25(8) 42(4) 0 7(2) 0
C44 32(4) 27(7) 42(4) 0 8(3) 0
C54 32(5) 25(7) 41(3) 0 9(3) 0
C64 32(4) 29(7) 39(3) 0 9(3) 0
C74 30(3) 83(8) 40(7) 0 10(4) 0
C84 33(3) 101(9) 52(11) 0 16(6) 0
C94 41(8) 153(12) 78(11) -63(8) 5(7) -13(8)
C114 30(10) 51(7) 41(3) 0 10(4) 0
C124 31(13) 86(9) 39(5) 0 11(6) 0
C134 49(13) 66(8) 47(7) 12(6) 13(8) -11(6)
F14 68(5) 49(8) 46(5) 0 -20(4) 0
F24 71(5) 101(16) 31(6) 0 13(5) 0
C154 31(3) 23(8) 34(2) 0 -1(2) 0
C164 35(3) 33(7) 36(3) 0 -4(3) 0
C174 58(4) 33(7) 35(3) 0 -9(3) 0
C184 69(5) 30(7) 25(4) 0 -3(3) 0
262
C194 60(5) 30(9) 30(2) 0 4(3) 0
C204 36(3) 24(8) 31(2) 0 2(2) 0
C214 32(3) 12(8) 34(3) 0 5(2) 0
C224 34(3) 49(8) 42(4) 0 11(3) 0
C234 29(4) 43(9) 51(6) 0 9(4) 0
C244 27(2) 60(8) 47(5) 0 2(4) 0
C254 27(2) 50(9) 37(4) 0 0(3) 0
N14 28(2) 38(7) 32(3) 0 3(2) 0
____________________________________________________________________
263
Appendix C-5 Hydrogen coordinates (x 10
4
) and isotropic displacement parameters
(Å
2
x 10
3
) for dfppy-Pt-sq.
____________________________________________________________________
x y z U(eq)
____________________________________________________________________
H41 1863 5000 4994 32
H61 451 5000 4586 30
H8A1 2531 3871 4732 52
H8B1 2544 6170 4720 52
H8C1 2881 4959 4373 52
H9A1 2578 3144 3516 88
H9B1 2033 3099 3311 88
H9C1 2237 1995 3872 88
H12A1 386 4234 5382 92
H12B1 459 6322 5658 92
H12C1 559 4444 6038 92
H13A1 1305 3178 6217 65
H13B1 1673 3251 5772 65
H13C1 1205 2035 5637 65
H161 -383 5000 2975 43
H181 -1207 5000 1476 55
H221 216 5000 622 57
264
H231 976 5000 396 62
H241 1607 5000 1094 59
H251 1498 5000 2045 51
H42 2007 0 626 39
H62 590 0 508 38
H8A2 2981 278 1579 94
H8B2 2620 985 1063 94
H8C2 2699 -1263 1177 94
H9A2 2660 1792 2344 137
H9B2 2112 1826 2367 137
H9C2 2330 2984 1887 137
H12A2 794 -200 -922 89
H12B2 629 1236 -465 89
H12C2 598 -1037 -377 89
H13A2 1538 1822 -786 79
H13B2 1857 1831 -194 79
H13C2 1376 2977 -268 79
H162 -329 0 1790 44
H182 -1226 0 2969 50
H222 138 0 4340 47
H232 878 0 4844 53
H242 1540 0 4388 57
H252 1484 0 3407 47
265
H43 1900 5000 4982 32
H63 482 5000 4689 29
H8A3 2545 3884 4679 51
H8B3 2562 6180 4658 51
H8C3 2876 4936 4289 51
H9A3 2543 3135 3462 88
H9B3 1997 3162 3264 88
H9C3 2198 2003 3816 88
H12A3 465 4250 5500 93
H12B3 557 6324 5779 93
H12C3 677 4427 6145 93
H13A3 1403 3111 6252 63
H13B3 1761 3257 5797 63
H13C3 1294 2030 5663 63
H163 1500 5000 2117 51
H183 1033 5000 448 62
H223 -507 5000 999 47
H233 -1179 5000 1445 52
H243 -1133 5000 2418 48
H253 -414 5000 2979 42
H44 2058 0 706 40
H64 641 0 429 40
H8A4 2965 288 1761 91
266
H8B4 2642 978 1209 91
H8C4 2716 -1266 1335 91
H9A4 2591 1856 2450 136
H9B4 2041 1769 2455 136
H9C4 2255 2984 1983 136
H12A4 953 -206 -953 77
H12B4 754 1239 -523 77
H12C4 714 -1033 -437 77
H13A4 1675 1857 -743 80
H13B4 1983 1746 -145 80
H13C4 1513 2968 -218 80
H164 1436 0 3394 42
H184 823 0 4830 51
H224 -630 0 3650 49
H234 -1253 0 2934 49
H244 -1125 0 1996 54
H254 -373 0 1742 46
____________________________________________________________________
267
Appendix D Crystal data for pq-Pt-sq.
Appendix D-1 Crystal data and structure refinement for pq-Pt-sq.
Empirical formula C29 H30 N O2 Pt
Formula weight 619.63
Temperature 163(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P2(1)/c
Unit cell dimensions a = 14.919(5) Å, α= 90º.
b = 6.3606(19) Å, b= 94.318(4) º.
c = 26.571(8) Å, g = 90º.
Volume 2514.3(13) Å
3
Z 4
Density (calculated) 1.637 Mg/m
3
Absorption coefficient 5.606 mm
-1
F(000) 1220
Crystal size 0.57 x 0.10 x 0.02 mm
3
Theta range for data collection 1.54 to 25.68º
Index ranges -15<=h<=18, -7<=k<=4, -32<=l<=31
Reflections collected 12322
Independent reflections 4749 [R(int) = 0.1525]
268
Completeness to theta = 25.68º 99.4 %
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 4749 / 0 / 299
Goodness-of-fit on F
2
1.053
Final R indices [I>2sigma(I)] R1 = 0.0896, wR2 = 0.2151
R indices (all data) R1 = 0.1601, wR2 = 0.2454
Largest diff. peak and hole 10.316 and -2.863 e. Å
–3
269
Appendix D-2 Atomic coordinates (x 10
4
) and equivalent isotropic displacement
parameters (Å
2
x 10
3
) for pq-Pt-sq.
U(eq) is defined as one third of the trace of the orthogonalized U
ij
tensor.
____________________________________________________________________
x y z U(eq)
____________________________________________________________________
Pt(1) 3034(1) 1467(1) 1896(1) 38(1)
O(1) 2153(8) 3710(20) 2070(4) 45(3)
O(2) 2913(8) 3310(20) 1209(4) 43(3)
N(1) 3906(9) -850(20) 1775(5) 39(4)
C(1) 1917(12) 5010(30) 1722(6) 45(6)
C(2) 2294(11) 4800(30) 1222(6) 39(5)
C(3) 1968(11) 6090(30) 810(6) 33(4)
C(4) 1311(11) 7530(30) 899(6) 31(4)
C(5) 911(11) 7750(30) 1381(6) 39(5)
C(6) 1194(13) 6610(30) 1787(6) 42(5)
C(7) 2341(11) 5700(30) 274(6) 35(4)
C(8) 2153(13) 3530(30) 109(7) 48(5)
C(9) 3369(13) 6170(40) 302(8) 57(6)
C(10) 1875(15) 7270(40) -120(7) 59(6)
C(11) 120(13) 9420(30) 1404(7) 46(5)
C(12) 273(15) 11440(30) 1109(9) 59(6)
C(13) -764(14) 8260(40) 1175(10) 72(7)
270
C(14) -9(17) 10000(50) 1955(9) 84(8)
C(15) 4551(11) -890(30) 1387(7) 36(4)
C(16) 4550(12) 830(40) 1052(7) 50(5)
C(17) 5194(13) 850(40) 669(7) 54(6)
C(18) 5778(16) -850(40) 617(8) 60(6)
C(19) 5750(12) -2590(40) 929(6) 46(5)
C(20) 5139(13) -2580(30) 1326(6) 43(5)
C(21) 5101(13) -4280(40) 1683(8) 53(5)
C(22) 4541(12) -4210(30) 2065(7) 41(5)
C(23) 3982(11) -2450(30) 2099(6) 35(4)
C(24) 3381(12) -2130(30) 2530(7) 39(5)
C(25) 3311(13) -3680(30) 2926(8) 54(6)
C(26) 2791(13) -3060(30) 3326(7) 45(5)
C(27) 2346(13) -1080(40) 3338(7) 55(6)
C(28) 2407(12) 330(40) 2935(7) 50(5)
C(29) 2940(12) -260(40) 2542(7) 45(5)
____________________________________________________________________
271
Appendix D-3 Bond lengths [Å] and angles [°] for pq-Pt-sq.
Pt(1)-N(1) 2.005(17)
Pt(1)-O(1) 2.018(13)
Pt(1)-C(29) 2.050(19)
Pt(1)-O(2) 2.165(12)
O(1)-C(1) 1.27(2)
O(2)-C(2) 1.33(2)
N(1)-C(23) 1.33(2)
N(1)-C(15) 1.47(2)
C(1)-C(2) 1.49(2)
C(1)-C(6) 1.50(3)
C(2)-C(3) 1.42(2)
C(3)-C(4) 1.37(2)
C(3)-C(7) 1.59(2)
C(4)-C(5) 1.46(2)
C(4)-H(4) 0.9500
C(5)-C(6) 1.34(2)
C(5)-C(11) 1.59(3)
C(6)-H(6) 0.9500
C(7)-C(8) 1.47(3)
C(7)-C(9) 1.56(2)
C(7)-C(10) 1.57(3)
C(8)-H(8A) 0.9800
272
C(8)-H(8B) 0.9800
C(8)-H(8C) 0.9800
C(9)-H(9A) 0.9800
C(9)-H(9B) 0.9800
C(9)-H(9C) 0.9800
C(10)-H(10A) 0.9800
C(10)-H(10B) 0.9800
C(10)-H(10C) 0.9800
C(11)-C(12) 1.53(3)
C(11)-C(14) 1.54(3)
C(11)-C(13) 1.59(3)
C(12)-H(12A) 0.9800
C(12)-H(12B) 0.9800
C(12)-H(12C) 0.9800
C(13)-H(13A) 0.9800
C(13)-H(13B) 0.9800
C(13)-H(13C) 0.9800
C(14)-H(14A) 0.9800
C(14)-H(14B) 0.9800
C(14)-H(14C) 0.9800
C(15)-C(20) 1.40(3)
C(15)-C(16) 1.41(3)
C(16)-C(17) 1.45(2)
273
C(16)-H(16) 0.9500
C(17)-C(18) 1.40(3)
C(17)-H(17) 0.9500
C(18)-C(19) 1.39(3)
C(18)-H(18) 0.9500
C(19)-C(20) 1.44(2)
C(19)-H(19) 0.9500
C(20)-C(21) 1.44(3)
C(21)-C(22) 1.36(3)
C(21)-H(21) 0.9500
C(22)-C(23) 1.40(3)
C(22)-H(22) 0.9500
C(23)-C(24) 1.52(2)
C(24)-C(29) 1.36(3)
C(24)-C(25) 1.45(3)
C(25)-C(26) 1.42(3)
C(25)-H(25) 0.9500
C(26)-C(27) 1.42(3)
C(26)-H(26) 0.9500
C(27)-C(28) 1.41(3)
C(27)-H(27) 0.9500
C(28)-C(29) 1.41(3)
C(28)-H(28) 0.9500
274
N(1)-Pt(1)-O(1) 175.7(5)
N(1)-Pt(1)-C(29) 80.0(7)
O(1)-Pt(1)-C(29) 95.8(7)
N(1)-Pt(1)-O(2) 106.0(5)
O(1)-Pt(1)-O(2) 78.2(5)
C(29)-Pt(1)-O(2) 171.3(6)
C(1)-O(1)-Pt(1) 116.3(11)
C(2)-O(2)-Pt(1) 112.3(10)
C(23)-N(1)-C(15) 114.2(15)
C(23)-N(1)-Pt(1) 118.9(12)
C(15)-N(1)-Pt(1) 126.6(12)
O(1)-C(1)-C(2) 119.3(16)
O(1)-C(1)-C(6) 121.3(14)
C(2)-C(1)-C(6) 119.1(16)
O(2)-C(2)-C(3) 126.1(14)
O(2)-C(2)-C(1) 113.4(15)
C(3)-C(2)-C(1) 120.5(16)
C(4)-C(3)-C(2) 117.2(14)
C(4)-C(3)-C(7) 124.1(14)
C(2)-C(3)-C(7) 118.7(15)
C(3)-C(4)-C(5) 124.1(15)
C(3)-C(4)-H(4) 118.0
275
C(5)-C(4)-H(4) 118.0
C(6)-C(5)-C(4) 121.8(17)
C(6)-C(5)-C(11) 121.4(16)
C(4)-C(5)-C(11) 116.8(15)
C(5)-C(6)-C(1) 117.4(15)
C(5)-C(6)-H(6) 121.3
C(1)-C(6)-H(6) 121.3
C(8)-C(7)-C(9) 111.0(16)
C(8)-C(7)-C(10) 109.5(15)
C(9)-C(7)-C(10) 107.2(16)
C(8)-C(7)-C(3) 110.0(15)
C(9)-C(7)-C(3) 109.7(13)
C(10)-C(7)-C(3) 109.4(14)
C(7)-C(8)-H(8A) 109.5
C(7)-C(8)-H(8B) 109.5
H(8A)-C(8)-H(8B) 109.5
C(7)-C(8)-H(8C) 109.5
H(8A)-C(8)-H(8C) 109.5
H(8B)-C(8)-H(8C) 109.5
C(7)-C(9)-H(9A) 109.5
C(7)-C(9)-H(9B) 109.5
H(9A)-C(9)-H(9B) 109.5
C(7)-C(9)-H(9C) 109.5
276
H(9A)-C(9)-H(9C) 109.5
H(9B)-C(9)-H(9C) 109.5
C(7)-C(10)-H(10A) 109.5
C(7)-C(10)-H(10B) 109.5
H(10A)-C(10)-H(10B) 109.5
C(7)-C(10)-H(10C) 109.5
H(10A)-C(10)-H(10C) 109.5
H(10B)-C(10)-H(10C) 109.5
C(12)-C(11)-C(14) 108.7(19)
C(12)-C(11)-C(13) 110.2(18)
C(14)-C(11)-C(13) 108.4(18)
C(12)-C(11)-C(5) 113.7(16)
C(14)-C(11)-C(5) 110.0(16)
C(13)-C(11)-C(5) 105.7(17)
C(11)-C(12)-H(12A) 109.5
C(11)-C(12)-H(12B) 109.5
H(12A)-C(12)-H(12B) 109.5
C(11)-C(12)-H(12C) 109.5
H(12A)-C(12)-H(12C) 109.5
H(12B)-C(12)-H(12C) 109.5
C(11)-C(13)-H(13A) 109.5
C(11)-C(13)-H(13B) 109.5
H(13A)-C(13)-H(13B) 109.5
277
C(11)-C(13)-H(13C) 109.5
H(13A)-C(13)-H(13C) 109.5
H(13B)-C(13)-H(13C) 109.5
C(11)-C(14)-H(14A) 109.5
C(11)-C(14)-H(14B) 109.5
H(14A)-C(14)-H(14B) 109.5
C(11)-C(14)-H(14C) 109.5
H(14A)-C(14)-H(14C) 109.5
H(14B)-C(14)-H(14C) 109.5
C(20)-C(15)-C(16) 119.6(17)
C(20)-C(15)-N(1) 123.1(16)
C(16)-C(15)-N(1) 117.3(16)
C(15)-C(16)-C(17) 119(2)
C(15)-C(16)-H(16) 120.7
C(17)-C(16)-H(16) 120.7
C(18)-C(17)-C(16) 121(2)
C(18)-C(17)-H(17) 119.5
C(16)-C(17)-H(17) 119.5
C(19)-C(18)-C(17) 121(2)
C(19)-C(18)-H(18) 119.7
C(17)-C(18)-H(18) 119.7
C(18)-C(19)-C(20) 119(2)
C(18)-C(19)-H(19) 120.5
278
C(20)-C(19)-H(19) 120.5
C(15)-C(20)-C(21) 116.3(17)
C(15)-C(20)-C(19) 121.3(18)
C(21)-C(20)-C(19) 122(2)
C(22)-C(21)-C(20) 121(2)
C(22)-C(21)-H(21) 119.4
C(20)-C(21)-H(21) 119.4
C(21)-C(22)-C(23) 118.5(19)
C(21)-C(22)-H(22) 120.7
C(23)-C(22)-H(22) 120.7
N(1)-C(23)-C(22) 126.3(16)
N(1)-C(23)-C(24) 110.9(17)
C(22)-C(23)-C(24) 122.8(17)
C(29)-C(24)-C(25) 121.1(18)
C(29)-C(24)-C(23) 116.5(17)
C(25)-C(24)-C(23) 122.4(18)
C(26)-C(25)-C(24) 115.2(18)
C(26)-C(25)-H(25) 122.4
C(24)-C(25)-H(25) 122.4
C(25)-C(26)-C(27) 123.2(16)
C(25)-C(26)-H(26) 118.4
C(27)-C(26)-H(26) 118.4
C(28)-C(27)-C(26) 119.3(18)
279
C(28)-C(27)-H(27) 120.3
C(26)-C(27)-H(27) 120.3
C(27)-C(28)-C(29) 118(2)
C(27)-C(28)-H(28) 121.1
C(29)-C(28)-H(28) 121.1
C(24)-C(29)-C(28) 123.4(18)
C(24)-C(29)-Pt(1) 112.7(14)
C(28)-C(29)-Pt(1) 123.6(16)
_____________________________________________________________
Symmetry transformations used to generate equivalent atoms:
280
Appendix D-4 Anisotropic displacement parameters (Å
2
x 10
3
) for pq-Pt-sq.
The anisotropic displacement factor exponent takes the form: -2p
2
[h
2
a*
2
U
11
+ ...
+ 2 h k a* b* U
12
]
____________________________________________________________________
U
11
U
22
U
33
U
23
U
13
U
12
____________________________________________________________________
Pt(1) 43(1) 40(1) 29(1) 4(1) 0(1) 2(1)
O(1) 50(7) 43(9) 40(7) 8(7) -5(5) -10(6)
O(2) 43(7) 54(10) 33(6) 1(6) 10(5) -2(7)
N(1) 42(8) 32(10) 42(8) 9(8) -1(6) -27(7)
C(1) 50(11) 65(17) 22(8) -5(9) 7(7) 18(10)
C(2) 40(10) 55(15) 20(8) -12(8) -5(7) -2(9)
C(3) 42(9) 34(13) 23(8) 0(8) 2(6) 7(8)
C(4) 42(9) 30(11) 21(8) 5(8) 4(6) 3(8)
C(5) 38(9) 46(13) 33(9) 3(9) -3(7) 1(9)
C(6) 64(12) 44(13) 17(7) -6(8) 1(7) 2(10)
C(7) 42(9) 40(12) 22(8) -10(8) -7(6) -2(9)
C(8) 59(11) 54(15) 30(9) 3(10) 6(8) 14(11)
C(9) 59(12) 69(18) 47(11) -16(11) 23(9) -18(12)
C(10) 80(15) 73(17) 27(9) 9(10) 22(9) 1(13)
C(11) 66(12) 31(12) 40(10) 6(10) 13(9) 19(10)
C(12) 58(12) 40(14) 80(15) -1(12) 16(11) 7(11)
281
C(13) 52(13) 62(19) 100(20) -17(14) 8(12) 0(12)
C(15) 38(9) 21(12) 47(10) -2(9) -5(7) -4(8)
C(16) 42(10) 65(16) 39(10) 2(10) -15(8) 5(10)
C(17) 52(11) 66(17) 49(11) -24(11) 28(9) -8(11)
C(18) 81(15) 54(16) 43(11) 7(11) -7(10) -2(13)
C(19) 49(11) 57(14) 33(10) -10(10) 6(8) 14(10)
C(20) 63(12) 39(13) 26(9) 5(9) -8(8) -3(10)
C(21) 61(12) 38(13) 57(12) -15(11) -20(10) 9(11)
C(22) 45(10) 34(12) 43(10) -4(9) -8(8) -18(9)
C(23) 36(9) 36(12) 31(9) -13(9) -6(7) -7(9)
C(24) 40(10) 27(12) 48(11) -11(9) -10(8) -14(9)
C(25) 54(12) 23(12) 80(15) 12(11) -18(10) -3(10)
C(26) 59(12) 44(15) 33(9) 25(9) -2(8) -14(10)
C(27) 45(10) 80(20) 35(10) 4(11) 2(8) 5(11)
C(28) 38(10) 69(16) 43(10) 6(11) -4(8) -4(10)
C(29) 42(10) 52(16) 41(10) 9(10) -6(8) -5(10)
____________________________________________________________________
282
Appendix D-5 Hydrogen coordinates (x 10
4
) and isotropic displacement parameters
(Å
2
x 10
3
) for pq-Pt-sq.
____________________________________________________________________
x y z U(eq)
____________________________________________________________________
H(4) 1104 8430 630 37
H(6) 947 6799 2103 50
H(8A) 2475 3229 -191 71
H(8B) 1505 3361 27 71
H(8C) 2353 2559 380 71
H(9A) 3691 5082 506 86
H(9B) 3485 7546 458 86
H(9C) 3576 6163 -39 86
H(10A) 2157 7155 -440 89
H(10B) 1944 8712 8 89
H(10C) 1235 6930 -174 89
H(12A) -108 12567 1228 88
H(12B) 120 11200 749 88
H(12C) 906 11861 1161 88
H(13A) -1285 9181 1203 108
H(13B) -849 6957 1361 108
283
H(13C) -703 7933 818 108
H(14A) 553 10583 2113 126
H(14B) -174 8743 2139 126
H(14C) -487 11055 1965 126
H(16) 4137 1957 1077 59
H(17) 5218 2022 450 65
H(18) 6198 -801 365 72
H(19) 6126 -3765 883 55
H(21) 5472 -5483 1650 64
H(22) 4531 -5316 2304 49
H(25) 3594 -5018 2919 64
H(26) 2737 -4002 3599 55
H(27) 2011 -720 3616 66
H(28) 2100 1643 2927 60
284
Appendix E TDDFT data of Ir-sq and Pt-sq complexes.
Appendix E-1 Orbital energies (in au) for Pt-sq.
Alpha occ. eigenvalues -- -0.28496 -0.26135 -0.25883 -0.24473 -0.24353
Alpha occ. eigenvalues -- -0.23371 -0.21661 -0.20017
Alpha virt. eigenvalues -- -0.07525 -0.05433 -0.01049 -0.00649 -0.00599
Alpha virt. eigenvalues -- -0.00148 0.01759 0.04004 0.04630 0.05048
Beta occ. eigenvalues -- -0.28144 -0.25509 -0.25375 -0.24229 -0.23239
Beta occ. eigenvalues -- -0.23109 -0.21202
Beta virt. eigenvalues -- -0.13252 -0.07311 -0.05394 -0.00393 -0.00310
Beta virt. eigenvalues -- 0.00365 0.01523 0.01841 0.04161 0.04692
(only MOs near HOMO-LUMO gap are listed)
285
Appendix E-2 TDDFT Excitation energies and oscillator strengths for Pt-sq.
Excited State 1: Spin -A 1.4751eV 840.49nm f=0.0035
116B ->118B -0.18056
117B ->118B 0.98202
Excited State 2: Spin -A 1.9482eV 636.40nm f=0.0003
112B ->118B -0.30497
115B ->118B 0.94558
Excited State 3: Spin -A 2.0951eV 591.77nm f=0.0409
110B ->118B 0.11041
113B ->118B 0.24877
114B ->118B -0.10325
116B ->118B 0.92845
117B ->118B 0.18234
Excited State 4: Spin -A 2.3001eV 539.04nm f=0.0004
111B ->118B -0.10187
112B ->118B 0.93497
115B ->118B 0.31185
Excited State 5: Spin -A 2.5100eV 493.97nm f=0.1009
118A ->119A -0.26157
113B ->118B -0.56852
114B ->118B 0.71573
116B ->118B 0.21927
286
Excited State 6: Spin -A 2.6051eV 475.93nm f=0.0995
118A ->119A 0.93623
113B ->118B -0.15066
114B ->118B 0.19570
Excited State 7: Spin -A 2.7171eV 456.30nm f=0.0025
114A ->119A 0.24242
114A ->120A -0.10104
115A ->119A -0.17332
117A ->119A -0.47751
110B ->118B 0.10466
113B ->118B 0.51331
114B ->118B 0.34317
114B ->119B -0.26320
116B ->119B 0.21952
117B ->119B 0.41976
Excited State 8: Spin -A 2.8759eV 431.11nm f=0.0081
117A ->119A 0.40032
113B ->118B 0.54098
114B ->118B 0.53843
114B ->119B 0.13251
116B ->118B -0.12520
116B ->119B -0.16544
287
117B ->119B -0.39364
288
Appendix E-3 TDDFT Excitation energies and oscillator strengths for Pt-sq.
Excited State 1: Spin -A 1.4134eV 877.23nm f=0.0030
115B ->118B -0.21908
117B ->118B 0.97862
Excited State 2: Spin -A 1.7822eV 695.70nm f=0.0004
112B ->118B -0.17481
116B ->118B 0.98128
Excited State 3: Spin -A 2.0517eV 604.31nm f=0.0272
111B ->118B 0.10936
113B ->118B 0.28534
114B ->118B -0.16187
115B ->118B 0.90972
117B ->118B 0.20396
Excited State 4: Spin -A 2.2893eV 541.58nm f=0.0003
112B ->118B 0.97096
116B ->118B 0.17906
Excited State 5: Spin -A 2.3569eV 526.04nm f=0.2123
113B ->118B -0.43317
114B ->118B 0.83828
115B ->118B 0.26539
Excited State 6: Spin -A 2.6974eV 459.64nm f=0.0055
114A ->119A 0.16245
289
115A ->119A -0.16736
117A ->119A -0.30886
111B ->118B 0.10734
113B ->118B 0.73292
114B ->118B 0.41164
114B ->119B -0.18751
115B ->118B -0.12505
115B ->119B 0.15017
117B ->119B 0.26591
Excited State 7: Spin -A 2.7850eV 445.19nm f=0.0623
113A ->119A -0.10213
114A ->119A 0.10490
118A ->119A 0.96676
114B ->119B -0.13752
Excited State 8: Spin -A 2.8832eV 430.02nm f=0.0052
114A ->119A -0.15274
115A ->119A 0.20637
117A ->119A 0.53434
118A ->119A 0.12870
113B ->118B 0.40777
113B ->120B -0.11576
114B ->118B 0.26851
114B ->119B 0.23615
290
115B ->118B -0.12794
115B ->119B -0.24260
117B ->119B -0.50045
291
Appendix E-4 TDDFT Excitation energies and oscillator strengths for model system
of Pt-sq.
Excited State 1: Spin -A 1.2194eV 1016.78nm f=0.0021
76B -> 78B 0.26638
77B -> 78B 0.95877
Excited State 2: Spin -A 1.6185eV 766.05nm f=0.0003
72B -> 78B -0.18810
75B -> 78B 0.97740
Excited State 3: Spin -A 1.8576eV 667.46nm f=0.0578
73B -> 78B -0.24093
74B -> 78B -0.19262
76B -> 78B 0.89196
77B -> 78B -0.24555
Excited State 4: Spin -A 2.0381eV 608.32nm f=0.0003
71B -> 78B -0.12119
72B -> 78B 0.96262
75B -> 78B 0.19132
Excited State 5: Spin -A 2.2706eV 546.04nm f=0.1070
73B -> 78B 0.58806
74B -> 78B 0.71753
76B -> 78B 0.27670
292
Appendix E-5 Orbital energies (in au) for Ir-sq.
Alpha occ. eigenvalues -- -0.24786 -0.24076 -0.23241 -0.23143 -0.22223
Alpha occ. eigenvalues -- -0.21827 -0.19023 -0.18740
Alpha virt. eigenvalues -- -0.06086 -0.05902 -0.04426 -0.04003 -0.00455
Alpha virt. eigenvalues -- 0.00161 0.00855 0.01508 0.02811 0.03104
Beta occ. eigenvalues -- -0.23944 -0.23715 -0.23033 -0.22494 -0.21940
Beta occ. eigenvalues -- -0.21132 -0.18599
Beta virt. eigenvalues -- -0.11929 -0.06026 -0.05882 -0.04406 -0.04004
Beta virt. eigenvalues -- 0.00812 0.00890 0.01515 0.02142 0.02822
(only MOs near HOMO-LUMO gap are listed)
293
Appendix E-6 TDDFT Excitation energies and oscillator strengths for Ir-sq.
Excited State 1: Spin -A 1.1514eV 1076.78nm f=0.0002
150B ->158B 0.14418
157B ->158B 0.98465
Excited State 2: Spin -A 1.6354eV 758.11nm f=0.0045
153B ->158B -0.10604
156B ->158B 0.99110
Excited State 3: Spin -A 2.1693eV 571.54nm f=0.0918
152B ->158B -0.26897
153B ->158B -0.11281
154B ->158B 0.51939
155B ->158B 0.76590
Excited State 4: Spin -A 2.2207eV 558.30nm f=0.0176
150B ->158B 0.12133
151B ->158B -0.10529
152B ->158B 0.63710
153B ->158B 0.67106
155B ->158B 0.29140
Excited State 5: Spin -A 2.4481eV 506.46 nm f=0.0034
157A ->160A -0.11194
149B ->158B -0.16129
153B ->158B 0.13710
294
154B ->158B 0.78696
155B ->158B -0.51288
157B ->160B 0.14125
Excited State 6: Spin -A 2.4906eV 497.81 nm f=0.0001
155A ->160A 0.18127
157A ->159A -0.62977
152B ->158B 0.11115
153B ->158B -0.11715
155B ->160B -0.15402
157B ->159B 0.69082
Excited State 7: Spin -A 2.5422eV 487.71nm f=0.0000
155A ->159A 0.19463
157A ->160A -0.63138
154B ->158B -0.14553
154B ->159B 0.10259
155B ->158B 0.12000
155B ->159B -0.16620
157B ->160B 0.69254
Excited State 8: Spin -A 2.5934eV 478.08nm f=0.0009
157A ->159A 0.14912
150B ->158B -0.56983
152B ->158B 0.59704
153B ->158B -0.48510
295
157B ->158B 0.12498
157B ->159B -0.10874
Excited State 9: Spin -A 2.6469eV 468.42nm f=0.0006
158A ->159A 0.93924
154B ->158B 0.10356
155B ->159B 0.10617
157B ->159B -0.12524
157B ->160B 0.15171
Excited State 10: Spin -A 2.6731eV 463.82nm f=0.0006
153A ->160A -0.10032
157A ->159A 0.17759
158A ->160A 0.90925
157B ->159B 0.27616
Excited State 11: Spin -A 2.7278eV 454.53nm f=0.0406
157A ->159A 0.68946
158A ->160A -0.30974
157B ->159B 0.58263
157B ->160B 0.11985
Excited State 12: Spin -A 2.7954eV 443.52nm f=0.0002
157A ->160A -0.10287
144B ->158B -0.10911
148B ->158B -0.14456
150B ->158B 0.73503
296
152B ->158B 0.34601
153B ->158B -0.48059
154B ->158B 0.13914
157B ->160B -0.11521
Excited State 13: Spin -A 2.7987eV 443.01nm f=0.0002
157A ->160A 0.69263
158A ->159A -0.10599
149B ->158B 0.14281
151B ->158B -0.19151
157B ->160B 0.59570
Excited State 14: Spin -A 2.8384eV 436.80nm f=0.0135
157A ->160A 0.12707
149B ->158B -0.51501
151B ->158B 0.77908
155B ->158B 0.10221
157B ->160B 0.16484
Excited State 15: Spin -A 2.9574eV 419.23nm f=0.0008
154A ->159A 0.14627
154A ->160A -0.18042
154A ->162A -0.14038
155A ->159A -0.32886
155A ->160A 0.13864
155A ->161A 0.15984
297
156A ->159A 0.16945
156A ->160A -0.25297
157A ->160A -0.14255
157A ->161A 0.18134
157A ->162A 0.20328
158A ->159A -0.18194
151B ->161B -0.10155
153B ->159B -0.16398
153B ->160B 0.20395
153B ->161B 0.10267
153B ->162B 0.14255
154B ->161B 0.10090
155B ->159B 0.39781
155B ->160B -0.16818
155B ->161B -0.11721
156B ->159B -0.12882
156B ->160B 0.20465
157B ->160B 0.15328
157B ->161B -0.21050
157B ->162B -0.2370
Excited State 16: Spin -A 2.9792eV 416.17nm f=0.0009
154A ->159A -0.14673
154A ->161A 0.13779
298
155A ->159A -0.14447
155A ->160A -0.21091
155A ->162A -0.17376
156A ->159A -0.22714
156A ->160A -0.17915
157A ->159A -0.12708
157A ->160A -0.12740
157A ->161A -0.34747
157A ->162A 0.14963
158A ->160A -0.16470
153B ->159B 0.19191
153B ->160B 0.16030
154B ->162B -0.14393
155B ->159B 0.14626
155B ->160B 0.26588
155B ->162B 0.13444
156B ->159B 0.20016
156B ->160B 0.18811
157B ->159B 0.11059
157B ->160B 0.10797
157B ->161B 0.40816
157B ->162B -0.17727
Excited State 17: Spin -A 3.0474eV 406.85nm f=0.0019
299
137B ->158B 0.11119
149B ->158B 0.78198
151B ->158B 0.55975
154B ->158B 0.15710
Excited State 18: Spin -A 3.0873eV 401.60nm f=0.0010
153A ->160A 0.11010
154A ->159A 0.17298
155A ->160A 0.21270
156A ->159A 0.28040
157A ->161A -0.47457
158A ->161A 0.14623
153B ->159B -0.22241
155B ->160B -0.26361
156B ->159B -0.26744
157B ->159B -0.10609
157B ->161B 0.56547
300
Appendix E-7 TDDFT Excitation energies and oscillator strengths for model system
of Ir-sq.
Excited State 1: Spin -A 0.8888eV 1394.91 nm f=0.0002
110B ->118B 0.14205
117B ->118B 0.98739
Excited State 2: Spin -A 1.4457eV 857.61 nm f=0.0019
116B ->118B 0.99207
Excited State 3: Spin -A 1.9818eV 625.61 nm f=0.0980
112B ->118B 0.11353
114B ->118B 0.39865
115B ->118B 0.86547
Excited State 4: Spin -A 2.1095eV 587.74 nm f=0.0033
111A ->123A -0.12721
117A ->124A -0.10197
110B ->118B -0.10860
111B ->118B 0.75441
113B ->118B -0.63334
Excited State 5: Spin -A 2.2178eV 559.05 nm f=0.0020
109B ->118B -0.20772
114B ->118B 0.87034
115B ->118B -0.43411
301
Appendix F TDDFT data for trans-isomer of Iridium dinuclear complex.
Appendix F-1 Excitation energies and oscillator strengths for trans-isomer of
dinuclear Iridium complex.
Excited State 1: Singlet-A 0.7985eV 1552.71nm f=0.0000
233 ->235 0.69617
Excited State 2: Singlet-A 0.8013eV 1547.22nm f=0.0002
232 ->235 0.69564
Excited State 3: Singlet-A 1.0817eV 1146.16nm f=0.4586
230 ->235 -0.17331
234 ->235 0.44554
Excited State 4: Singlet-A 1.4522eV 853.76nm f=0.0002
229 ->235 0.11446
231 ->235 0.66247
Excited State 5: Singlet-A 1.6760eV 739.76nm f=0.2209
230 ->235 0.66446
Excited State 6: Singlet-A 1.9052eV 650.78nm f=0.0002
229 ->235 0.67731
Excited State 7: Singlet-A 1.9220eV 645.07nm f=0.0047
228 ->235 0.69860
Excited State 8: Singlet-A 1.9974eV 620.72nm f=0.0004
221 ->235 -0.14724
225 ->235 0.12524
302
227 ->235 0.64867
Excited State 9: Singlet-A 2.0730eV 598.08nm f=0.0762
226 ->235 0.67103
Excited State 10: Singlet-A 2.1241eV 583.71nm f=0.0001
221 ->235 -0.23716
223 ->235 0.17330
225 ->235 0.59070
227 ->235 -0.17080
Excited State 11: Singlet-A 2.2195eV 558.61nm f=0.0044
224 ->235 0.69501
Excited State 12: Singlet-A 2.2615eV 548.23nm f=0.0000
221 ->235 -0.36324
223 ->235 0.49156
225 ->235 -0.32513
Excited State 13: Singlet-A 2.3772eV 521.56nm f=0.0400
222 ->235 0.68604
226 ->235 -0.10853
Excited State 14: Singlet-A 2.3939eV 517.92nm f=0.0001
221 ->235 0.51085
223 ->235 0.46011
225 ->235 0.10743
Excited State 15: Singlet-A 2.6089eV 475.23nm f=0.0001
232 ->238 0.12430
303
234 ->236 0.66216
234 ->237 0.13973
Excited State 16: Singlet-A 2.6104eV 474.97nm f=0.0016
233 ->239 -0.11424
234 ->236 -0.15200
234 ->237 0.64579
Excited State 17: Singlet-A 2.6172eV 473.72nm f=0.0001
219 ->235 -0.24368
220 ->235 0.28604
232 ->236 0.21823
233 ->237 -0.20953
234 ->237 -0.12446
234 ->238 0.44242
234 ->239 0.15193
Excited State 18: Singlet-A 2.6211eV 473.02nm f=0.0027
232 ->236 -0.21394
232 ->237 0.14470
233 ->236 -0.14589
233 ->237 -0.20044
234 ->237 -0.10063
234 ->238 -0.18486
234 ->239 0.54561
Excited State 19: Singlet-A 2.6297eV 471.48nm f=0.0001
304
219 ->235 -0.36081
220 ->235 0.43466
232 ->236 -0.12557
233 ->237 0.11617
234 ->238 -0.33014
234 ->239 -0.10893
Excited State 20: Singlet-A 2.6728eV 463.88nm f=0.0185
232 ->236 -0.50073
233 ->236 -0.15178
233 ->237 0.20803
234 ->238 0.35395
305
Appendix F-2 Orbital energies (in au) for trans-isomer of dinuclear complex.
Alpha occ. eigenvalues -- -0.24170 -0.23847 -0.23613 -0.23235 -0.23086
Alpha occ. eigenvalues -- -0.22834 -0.22461 -0.22160 -0.22060 -0.21704
Alpha occ. eigenvalues -- -0.21024 -0.18549 -0.18542 -0.17337
Alpha virt. eigenvalues -- -0.13594 -0.06002 -0.05988 -0.05854 -0.05850
Alpha virt. eigenvalues -- -0.04391 -0.04369 -0.03967 -0.03958 -0.03310
Alpha virt. eigenvalues -- -0.00686 0.00866 0.00876 0.01184 0.01575
306
Appendix G TDDFT data for cis-isomer of Iridium dinuclear complex.
Appendix G-1Orbital Energies (in au) for cis-isomer of dinuclear complex.
Occupied MOs
-0.23908 -0.23892 -0.23549 -0.23294 -0.22980
-0.22853 -0.22467 -0.22269 -0.22129 -0.21711
-0.20785 -0.18556 -0.18548 -0.17236
Virtual MOs
-0.12787 -0.05801 -0.05769 -0.05609 -0.05574
-0.04199 -0.04136 -0.03795 -0.03742 -0.02656
-0.00092 0.01107 0.01122 0.01781 0.01807
NB HOMO=234, LUMO=235
307
Appendix G-2 TDDFT excitation energies and oscillator strengths for cis-isomer of
dinuclear complex.
Excited State 1: Singlet-A 1.0121eV 1225.03nm f=0.0039
232 ->235 0.31221
233 ->235 0.61859
Excited State 2: Singlet-A 1.0158eV 1220.58nm f=0.0001
232 ->235 0.62246
233 ->235 -0.31603
Excited State 3: Singlet-A 1.3861eV 894.46nm f=0.6861
218 ->235 0.11487
230 ->235 -0.16726
234 ->235 0.45979
Excited State 4: Singlet-A 1.5958eV 776.95nm f=0.0050
231 ->235 0.66577
Excited State 5: Singlet-A 1.8680eV 663.73nm f=0.1883
230 ->235 0.67093
Excited State 6: Singlet-A 2.1104eV 587.49nm f=0.0185
223 ->235 -0.15180
225 ->235 -0.22514
227 ->235 0.23006
229 ->235 0.57051
Excited State 7: Singlet-A 2.1703eV 571.26nm f=0.0002
225 ->235 -0.10128
308
227 ->235 0.24708
228 ->235 0.60928
229 ->235 -0.19675
Excited State 8: Singlet-A 2.1762eV 569.73nm f=0.0000
223 ->235 -0.12842
225 ->235 -0.20410
227 ->235 0.46142
228 ->235 -0.34066
229 ->235 -0.30631
Excited State 9: Singlet-A 2.2742eV 545.19nm f=0.0077
222 ->235 0.10086
223 ->235 0.17434
225 ->235 0.51809
227 ->235 0.37800
Excited State 10: Singlet-A 2.3064eV 537.56nm f=0.0139
226 ->235 0.66123
Excited State 11: Singlet-A 2.4485eV 506.36nm f=0.0053
223 ->235 -0.12831
224 ->235 0.67489
Excited State 12: Singlet-A 2.4678eV 502.41nm f=0.0014
222 ->235 0.13610
223 ->235 0.59289
224 ->235 0.15504
309
225 ->235 -0.29141
Excited State 13: Singlet-A 2.6142eV 474.27nm f=0.0131
221 ->235 0.49382
222 ->235 -0.46237
223 ->235 0.10877
Excited State 14: Singlet-A 2.6165eV 473.85nm f=0.0092
221 ->235 0.46642
222 ->235 0.47284
223 ->235 -0.17196
Excited State 15: Singlet-A 2.6396eV 469.71nm f=0.0000
232 ->238 -0.11324
234 ->236 0.63685
234 ->237 -0.20208
Excited State 16: Singlet-A 2.6417eV 469.34nm f=0.0063
234 ->236 0.19037
234 ->237 0.64846
Excited State 17: Singlet-A 2.6684eV 464.64nm f=0.0006
232 ->236 -0.26486
234 ->236 0.14583
234 ->238 0.61681
Excited State 18: Singlet-A 2.6716eV 464.08nm f=0.0009
233 ->237 0.22833
233 ->239 0.18937
310
234 ->239 0.61857
Excited State 19: Singlet-A 2.7244eV 455.08nm f=0.0352
232 ->236 0.58932
233 ->236 -0.15655
234 ->238 0.28616
Excited State 20: Singlet-A 2.7326eV 453.73nm f=0.0418
232 ->237 0.17453
233 ->237 0.60150
234 ->239 -0.23760

Abstract (if available)

Abstract Techniques are developed for the combinatorial screening of metal catalysts towards the oxidation of water. The electrochemical reaction is thermodynamically feasible but kinetically labile at the anode. The use of metal particles as catalysts at the anode can lower the overpotential for the reaction. Thermal output method of combinatorial screening is explored as a qualitative and fast measurement of activity of platinum-group catalysts. The activity is monitored as a function of the heat dissipated across a fixed resistor in series with the cell. The more active a catalyst, a larger current flows through the cell for the same applied potential resulting in a larger dissipation of heat across the resistor that is imaged by an infrared camera as greater heating. The choice of electrolytes is also explored. The preparation of metal catalyst using thermal reduction of metal precursor solutions is described. The catalytic surface is characterized by microscopy (SEM) and spectroscopy (XPS).

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University of Southern California Dissertations and Theses

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Design and modification of electrocatalysts for use in fuel cells and CO₂ reduction

Asset Metadata

Creator Hirani, Bhavna (author)

Core Title Combinatorial screening methods for metal catalysts and cyclometalated iridium and platinum complexes with non-innocent ligands

School College of Letters, Arts and Sciences

Degree Doctor of Philosophy

Degree Program Chemistry

Publication Date 04/25/2009

Defense Date 02/21/2007

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag catalysts,combinatorial,cyclometalated,electrochemistry,electronic,iridium,non-innocent ligands,OAI-PMH Harvest,oxidation,platinum,screening,water

Language English

Advisor Thompson, Mark E. (committee chair), Bau, Robert (committee member), Mansfeld, Florian B. (committee member)

Creator Email hirani@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-m459

Unique identifier UC1132259

Identifier etd-Hirani-20070425 (filename),usctheses-m40 (legacy collection record id),usctheses-c127-495539 (legacy record id),usctheses-m459 (legacy record id)

Legacy Identifier etd-Hirani-20070425.pdf

Dmrecord 495539

Document Type Dissertation

Rights Hirani, Bhavna

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Repository Name Libraries, University of Southern California

Repository Location Los Angeles, California

Repository Email cisadmin@lib.usc.edu