View Plots of the Lowest Energy Structures of M22pt – M25pt4

THE EFFECT OF METAL CONTAINING LIGANDS ON THE METAL-METAL

QUADRUPLE BOND: STRUCTURE, SYNTHESIS, AND PHOTOPHYSICS

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

Christopher Blair Durr

Graduate Program in Chemistry

The Ohio State University

2015

Dissertation Committee:

Dr. Malcolm H. Chisholm – Advisor

Dr. Claudia Turro

Dr. Patrick M. Woodward

Dr. Hamish Fraser

Christopher Blair Durr

2015

Abstract

The world’s ever increasing demand for fossil fuels has lead to a renewed focus by the scientific community to develop energy sources that are clean, renewable, and economical. One of the most promising emerging technologies is photovoltaic cells that can turn sunlight directly into energy or into fuels such as methane or hydrogen. In order for these cells to replace preexisting energy sources, it is necessary to increase their efficiency and processability while also curtailing cost.

The focus of this work will be on electron donating materials, the main purpose of which is to absorb light and cause charge transfer to occur in the cell. To increase efficiency of donor materials several factors must be considered. Firstly, the material must capture as much of the solar spectrum as possible, which ranges from 400 nm to well over 1200 nm.

Thus a material that has a broad, tunable absorption band is key to capturing as much of this light as possible. Secondly, the absorbing material must efficiently absorb photons by having a high molar absorptivity. Lastly, when light hits the donor material there must be a sufficient separation of the electron-hole pair. The material must stay in this charge separated state long enough to undergo charge transfer to an acceptor and thus begin the circuit.

M2 quadruply bonded complexes, where M2 = Mo2, MoW or W2 have optical properties ideal for electron donating materials. Compounds of this type have a fully allowed metal- ii to-ligand charge-transfer (MLCT) band that is tunable from 400 nm to 1200 nm based on the choice of metal and ligand. This absorption is quite intense with extinction coefficients from 20,000 to nearly 100,000 M-1cm-1. The MLCT is caused by the transfer of an electron from a M2δ orbital to a ligand based π* orbital. The molecule exists in this singlet MLCT state for 3 – 25 ps before intersystem crossing to either a 3δδ* or 3MLCT state lasting from 2 ns - >75 μs.

This work will discuss the synthesis, characterization and photophysics of M2 complexes and their interactions with metal containing ligands. By using organometallic or metal- organic ligands it is possible to cover more of the solar spectrum as the metal containing ligands chosen also have allowable optical transitions that are possible to tune. The ligands discussed herein contain chromium, rhenium, and platinum which each have interesting photophysical properties of their own.

In the initial chapters metal carbonyls of chromium and rhenium were studied as the CO infrared stretches served as markers to follow using femtosecond time-resolved infrared spectroscopy. The effect of additional metal d-orbitals on the molecules excited state dynamics was discussed in detail for these compounds. A theoretical study of M2-Pt acetylide polymers was also conducted to determine the electronic structure and optical properties of future materials. Isonicotinic N-oxide is investigated as a ligand for Mo2 systems and the resulting complexes are attached to solid state films consisting of TiO2,

NiO and Indium-Tin oxide. Finally, the solid state packing of Mo2 halobenzoate complexes is discussed as molecules of this form tend to form interesting halogen- halogen interactions.

iii

To Sarah

Acknowledgments

It has been a long and exciting road to get to a point where I may finally write an

Acknowledgment to this thesis. Forgive me in advance for any errors or omissions in this section of the work, as one’s English tends to atrophy after years of writing in third person.

There are so many people that I need to thank, incredible individuals who have helped me get to where I am today. In many ways, the chapters that follow are as much theirs as mine. First and foremost, I need to thank my parents, Virginia and Robert, and my sister

Stephanie for putting up with years of my pseudo-scientific endeavors. From messes in the kitchen to destroyed computers in the basement, they have always encouraged my curiosities.

However, despite this curiosity, my growing passion for chemistry may have never fully taken form without the help and dedication of my first mentor, Mr. David Weaver. He found a way to make chemistry come alive in ways that few could. I can wholeheartedly say, after spending nearly my entire life in school, Mr. Weaver is without a doubt one of the finest educators I’ve ever known.

Shortly after my first year at Kent State University, I met Dr. Scott Bunge and joined his lab as an Undergraduate researcher. Scott had a tremendous influence on my decision to

v get a Ph.D., and he taught me a love for inorganic chemistry, particularly for synthesis and structure, which remains with me to this day. Everything I have accomplished in

Graduate School stemmed from the head start I gained by working in his lab, and for that

I am eternally grateful.

My decision of where to attend Graduate School was, in retrospect, a simple one. I wanted to work for a leader in the field of inorganic chemistry, someone who would let me pursue my own ideas, and someone who was a great person. With those things in mind, Dr. Malcolm Chisholm was an easy choice. Malcolm has been every bit the mentor

I expected him to be. He has always been there to guide me through the treacherous years of my Ph.D., all the while encouraging me to explore new ideas and possibilities. I am incredibly proud to have worked with him for the past five years and I hope to pass on everything he has taught me to generations to come. Even if I work every day for the rest of my life, I will never be able to repay him for all he’s done.

There are several other people who have been incredibly helpful throughout my time at

Ohio State. Dr. Vesal Naseri was instrumental early in my career for teaching me the finer points of synthesis and for many helpful discussions. Dr. Claudia Turro has been like a second advisor to me, and she was always there when I needed to bounce an idea around or get an opinion. Furthermore, Dr. Turro has always believed in me, and for that

I can’t thank her enough. Finally, Dr. Judy Gallucci has taught me more about crystallography than I ever thought possible. She has been infinitely patient with me over the years and has introduced me to an incredible community of scientists.

I cannot overstate how inspiring and helpful my colleagues, both in and out of the

Chisholm group, have been to me. We have a saying in the group that goes, “You learn the most from your brothers and sisters,” and I believe that every bit of that is true. I could not have asked for a better group of people to learn and work with all of these years, and I would like to thank all of them, both past and present. In particular I feel it necessary to mention a few of them by name, as they had substantial contributions to this document. Dr. Samantha Brown-Xu did all of the fs-TRIR and fs-TA seen in this document. She also contributed greatly to Chapters 3 and 4, and her initial work on TiO2 was the inspiration for Chapter 6. Any photophysics I know, I know because of Sam. Dr.

Thomas Spilker was responsible for all of the emission data, and ns-TA seen herein.

Furthermore he conducted the synthesis for the crystal engineering in Chapter 7. Tom is an excellent synthetic chemist, left-fielder, and friend. While Dr. Sharlene Lewis,

Vagulejan Balasanthiran, and Philip Young did not contribute directly to this work, they have all been a joy to work with. Sharlene and Bala are two of the finest synthetic chemists I’ve had the opportunity to meet and both are exceedingly fine people. It’s personally been a pleasure to watch Phil grow from someone constantly asking me questions to constantly answering mine. He’s an exceptional chemist both at the bench and in the classroom. Last but certainly not least, Dr. Bryan Albani who, without contributing any words to this dissertation, made it entirely possible through his support and friendship from our first day onward.

I started this section with family and thus it feels fitting to end with family. It’s funny how family comes in many different guises. There are those we are born into, those we

vii marry into and those we are adopted by. My best friend Mark Spillan is a member of the latter, and without him I surely wouldn’t be here today. My “in-laws”, Mike, Lorrie,

Emily and Kyle have filled my life with more joy and laughter than I ever thought possible, and their support has meant the world to me. (Kyle and Emily deserve a bit of extra credit having edited my tortured writing, and trying in vain to explain to me when one is to use commas appropriately). This family is growing still with Stephanie, Jason and little Arianna, who certainly won’t stay little for as long as I’d like her to.

Lastly, there’s my bride Sarah. To whom, in the end, all of this is dedicated. She has been there through the highs and the lows, the dark and the light, just like she said she would be. I never would have made it through, had it not been for her love and support. I thank the good Lord everyday that she’s my wife.

viii

Vita

2010...... B.S. Chemistry, Kent State University

2010 – 2012...... Graduate Teaching Associate, Department

of Chemistry and Biochemistry, The Ohio

State University

2012 – 2014...... Graduate Research Associate, Department

of Chemistry and Biochemistry, The Ohio

State University

2014 – Present ...... Presidential Fellow, Department of

Chemistry and Biochemistry, The Ohio

State University

Publications

i 1. “(TMP)ZnN(SiMe3)2, [(TMP)Zn(µ-O Pr)]2 and (TMP)Zn[OCMe2C(O)OEt]. Their role in the Ring-Opening of rac-lactide and caprolactone where TMP = 1,5,9 - trimesityldipyrrolemethene” V. Balasanthiran, M. H. Chisholm, K. Choojun, C. B. Durr, and P. M. Wambua, Inorganic Chemistry, 2015, In Preparation.

2. “TMPMg(nBu)L, where L = THF, 2-MeTHF, pyridine and dimethylaminopyridine and TMP = 1,5,9 - trimesityldipyrrolemethene and reaction with lactide and ε-caprolactone” V. Balasanthiran, M. H. Chisholm, K. Choojun, C. B. Durr, and Pasco M. Wambua, Dalton Transactions, 2015, In Preparation.

3. “BDI*MgX(L) where X = nBu and OtBu and L = THF, py, and DMAP. The rates t i of kinetic exchange of L where BDI* = CH2{C( Bu)N-2,6-( Pr)2C6H3}2” V. Balasanthiran, M. H. Chisholm, and C. B. Durr, Polyhedron, 2015, ASAP, DOI: 10.1016/j.poly.2015.02.024.

4. “Bismuth – Lithium Bonding in the Ion Pairs: LiBiL2 where L = a Porphyrin or Salen Ligand” V. Balasanthiran, M. H. Chisholm, and C. B. Durr, Dalton Transactions, 2015, ASAP, DOI: 10.1039/C5DT00256G.

5. “Electronic and Spectroscopic Properties of Avobenzone Derivatives Attached to

Mo2 Quadruple Bonds” M. H. Chisholm, C. B. Durr, T. L. Gustafson, W. T. Kender, T. F. Spilker and P. J. Young, Journal of the American Chemical Society, 2015, ASAP, DOI: 10.1021/jacs.5b01495.

6. “Steric and Electronic Factors Associated with the Photoinduced Ligand Exchange of Bidentate Ligands Coordinated to Ru(II)” B. A. Albani, T. Whittemore, C. B. Durr, and C. Turro, Photochemistry and Photobiology, 2015, ASAP, DOI: 10.1111/php.12392.

7. “MM Complexes Supported by Vinylbenzoate Ligands: Synthesis, Characterization, Photophysical Properties and Application as a Synthon” S. E. Brown-Xu, M. H. Chisholm, C. B. Durr, T. F. Spilker and P. J. Young, Chemical Science, 6, 2015, 1780 – 1791.

8. “Molecular Ordering by Halide-Halide Interactions in Dimolybdenum p- halobenzoates” M. H. Chisholm, C. B. Durr and T. F. Spilker, Inorganica Chimica Acta, 424, 2015, 300 – 307.

9. “Isomerization Initiated by Photoinduced Ligand Dissociation in Ru(II) Complexes with the Ligand 2-p-tolylpyridinecarboxaldimine” B. A. Albani, C. B. Durr, B. Peña, K. R. Dunbar, C. Turro, Dalton Transactions, 43, 2014, 17828 – 17837.

10. “Unusually Efficient Pyridine Photodissociation from Ru(II) Complexes with Sterically Bulky Bidentate Ancillary Ligands” J. D. Knoll, B. A. Albani, C. B. Durr, and C. Turro, Journal of Physical Chemistry - A, 118, 2014, 10603 – 10610.

11. “cis-Thienyl Carboxylates Bound to Mo2 Quadruply Bonded Units and Titanium Dioxide” S. E. Brown-Xu, M. H. Chisholm, C. B. Durr, T. L. Gustafson, and T. F. Spilker, Journal of the American Chemical Society, 136, 2014, 11428 – 11435.

12. “4-Nitrophenyl and 4’-nitro-1,1’-biphenylcarboxylates attached to Mo2 quadruple bonds: Ground versus excited state M2δ – Ligand conjugation” B. G. Alberding, M. H. Chisholm, C. B. Durr, J. C. Gallucci, Y. Ghosh, and T. F. Spilker, Dalton Transactions, 43, 2014, 11397-11403

13. “Molybdenum-Molybdenum Quadruple Bonds Supported by 9,10-Anthraquinone Carboxylate Ligands. Molecular and Electronic Structures and Ground State and Photoexcited State Redox Properties” S. E. Brown-Xu, M. H. Chisholm, C. B. Durr, S. A. Lewis, T. F. Spilker and P. J. Young, Chemical Science, 4, 2014, 2657 - 2666.

14. “On the Molecular Structure and Bonding in a Lithium Bismuth Porphyrin

Complex: LiBi(TPP)2” V. Balasanthiran, M. H. Chisholm, and C. B. Durr, Angewandte Chemie International Edition. 53, 2014, 1594-1597.

15. “Mo2 Paddlewheel Complexes Functionalized with a Single MLCT, S1 Infrared- Active Carboxylate Reporter Ligand: Preparation and Studies of Ground and Photoexcited States” S. E. Brown-Xu, M. H. Chisholm, C. B. Durr, S. A. Lewis, T. F. Spilker, and P. J. Young. Inorganic Chemistry. 53, 2014, 637-644.

16. “Ethyl 2-hydroxy-2-methylpropanoate derivatives of magnesium and zinc. The effect of chelation on the homo- and copolymerization of lactide and ε- caprolactone” V. Balasanthiran, M. H. Chisholm, K. Choojun and C. B. Durr. Dalton Transactions. 43, 2014, 2781-2788.

17. “Concerning the ground state and S1 and T1 photoexcited states of the homoleptic quadruply bonded complexes Mo2(O2CC6H4-p-X)4 where X = C≡C-H or C≡N.” S. E. Brown-Xu, M. H. Chisholm, C. B. Durr, and T. F. Spilker. Journal of Physical Chemistry – A. 117, 2013, 13893-13898.

18. “Selective Photoinduced Ligand Exchange in a New Tris-Heteroleptic Ru(II) Complex” B. A. Albani, C. B. Durr, and C. Turro. Journal of Physical Chemistry – A. 117, 2013, 13885-13892.

19. “Modulating the M2δ-to-Ligand Charge Transfer Transition by the Use of Diarylboron Substituents” S. E. Brown-Xu, M. H. Chisholm, C. B. Durr, and T. F. Spilker and P. J. Young, Dalton Transactions, 42, 2013, 14491-14497.

20. “Single-site Bismuth Alkoxide Catalysts for the Ring-Opening Polymerization of Lactide and ε-Caprolactone” V. Balasanthiran, M. H. Chisholm, and C. B. Durr, Dalton Transactions, 42, 2013, 11234-11241.

21. “Molecular and Electronic Structure of MM Quadruply Bonded Complexes

Containing O2CC6H4N(Ph)2 Supporting Ligands” M. H. Chisholm, C. B. Durr, S. L. Lewis, Polyhedron. 64, 2013, 339-345.

22. “Metal-Metal Quadruple Bonds Supported by 5-Ethynylthiophene-2-carboxylato Ligands: Preparation, Molecular and Electronic Structures, Photoexcited State Dynamics, and Application as Molecular Synthons” S. E. Brown-Xu, M. H. Chisholm, C. B. Durr, and T. F. Spilker, The Journal of the American Chemical Society, 135 (22), 2013, 8254-8259.

23. “Coordination of N,N-Chelated Re(CO)3Cl units across a Mo2 quadruple bond: Synthesis, characterization, and photophysical properties of a Re-Mo2-Re triad and its component pieces” S. E. Brown-Xu, M. H. Chisholm, C. B. Durr, T. L. Gustafson and T. F. Spilker, The Journal of Physical Chemistry A, 117(29), 2013, 5997-6006.

24. “MM Quadruple bonds supported by cyanoacrylate ligands. Extending photon harvesting into the near infrared and studies of the MLCT states” S. E. Brown-Xu, M. H. Chisholm, C. B. Durr, V. Naseri and T. F. Spilker, Chemical Science, 4, 2013, 2105-2116

25. “Electronic Structure and Excited-State Dynamics of the Molecular Triads: trans- i 6 i M2(T PB)2[O2CC6H5-η -Cr(CO)3]2, Where M = Mo or W, and T PB = 2,4,6- triisopropylbenzoate” S. E. Brown-Xu, M. H. Chisholm, C. B. Durr, T. L.

xii

Gustafson, V. Naseri and T. F. Spilker, Journal of the American Chemical Society, 134 (51), 2012, 20820-20826.

26. “Oxalate Bridged MM Quadruply Bonded Oligomers: Considerations of Electronic Structure and Synthetic Strategies” M. H. Chisholm, C. B. Durr, C. M. Hadad, and T. F. Spilker. Journal of Cluster Science, 23, 2012, 767-780.

27. "A Family of 1,1,3,3-Tetraalkylguanidine (H-TAG) Solvated Zinc Aryloxide Pre- Catalysts for the Ring-Opening Polymerization of rac-Lactide" J. J. Ng, C. B. Durr, J. M. Lance and S. D. Bunge. European Journal of Inorganic Chemistry, 9 , 2009, 1424-1430.

28. "1,1,3,3-Tetramethylguanidine solvated lanthanide aryloxides: Pre-catalysts for intramolecular hydroalkoxylation" T. E. Janini, R. Rakosi III, C. B. Durr, J. A. Burtke and S. D. Bunge. Dalton Transactions, 47, 2009, 10601-10608.

Fields of Study

Major Field: Chemistry

xiii

Table of Contents

Abstract ...... ii

Acknowledgments...... v

Vita ...... ix

List of Tables ...... xx

List of Figures ...... xxiii

List of Schemes ...... xxxii

CHAPTER 1 : INTRODUCTION ...... 1

1.1 The Metal-Metal Bond ...... 1

1.1.1 Discovery ...... 1

1.1.2 Mo2 and W2 Paddlewheel Complexes ...... 5

1.1.3 Current Developments in Group 6 Metal-Metal Paddlewheels ...... 8

1.1.4 Synthesis ...... 9

1.1.5 Bonding ...... 12

1.2 Photophysics of Mo2 and W2 Paddlewheel Complexes ...... 15

1.2.1 Electronic Spectroscopy ...... 15

1.2.2 Excited State Spectroscopy ...... 17

xiv

1.2.3 Ultra-fast Spectroscopy ...... 19

1.3 π-Conjugated Metal Polymers ...... 21

1.3.1 Model Compounds ...... 23

1.3.2 Pt-Acetylide Polymers ...... 23

1.3.3 M2-Oxylate Polymers ...... 26

1.4 Photovoltaic Cells ...... 28

1.4.1 Bulk Heterojunction Cells ...... 29

1.4.2 Dye Sensitized Solar Cells ...... 33

1.5 Statement of Purpose ...... 36

1.5.1 Hybrid Type II/III Metal Polymers ...... 36

1.5.2 Chapter Summary ...... 37

CHAPTER 2 : MATERIALS AND METHODS ...... 39

2.1 General Experimental ...... 39

2.2. Steady-state spectroscopy ...... 40

2.3. Transient absorption spectroscopy ...... 40

2.4. Time-Resolved Infrared Spectroscopy ...... 41

CHAPTER 3 : THE EFFECT OF Cr(CO)3 PIANO STOOL LIGANDS ON THE M2

CORE: SYNTHESIS, CHARACTERIZATION AND PHOTOPHYSICS ...... 44

3.1 Introduction ...... 44

3.2 Results and Discussion ...... 47

3.2.1 Synthesis ...... 47

3.2.2 Single Crystal X-Ray Structure ...... 49

3.2.3 Ground-State Infrared Spectroscopy ...... 51

3.2.4 Electronic Absorption Spectra ...... 53

3.2.5 Luminescence Studies ...... 54

3.2.6 Computational Studies ...... 55

3.2.7 Time-Resolved Studies ...... 58

3.3 Conclusions ...... 65

3.4 Experimental ...... 65

CHAPTER 4 : THE STUDY OF PMTReCl(CO)3 AND ITS EFFECT ON THE

PHOTOPHYSICS OF Mo2 PADDLEWHEELS ...... 68

4.1 Introduction ...... 68

4.2 Results and discussion ...... 70

4.2.1 Synthesis ...... 70

4.2.2 Solid State Molecular Structure ...... 73

4.2.3 UV-Visible Absorption Spectroscopy ...... 75

4.2.4 Luminescence Studies ...... 77

4.2.5 Ground State Infrared ...... 80

xvi

4.2.6 Electronic Structure Calculations ...... 81

4.2.7 EPR Studies ...... 85

4.2.8 Ultra-fast Spectroscopy ...... 87

4.3 Conclusions ...... 95

4.4 Experimental ...... 96

CHAPTER 5 : A COMPUTATIONAL STUDY OF M2-Pt ACETYLIDE HYBRID

POLYMERS ...... 99

5.1 Introduction ...... 99

5.2 Approximations and Methods ...... 103

5.3 Results and Discussion ...... 104

5.3.1 Electronic Structure ...... 107

5.3.2 Optical Properties ...... 113

5.4 Conclusions ...... 117

CHAPTER 6 : THE EFFECT OF PYRIDYL N-OXIDE LIGANDS ON Mo2

PADDLEWHEELS AND THEIR POTENTIAL APPLICATION AS ANCHORING

GROUPS ...... 118

6.1 Introduction ...... 118

6.2 Results and Discussion ...... 120

6.2.1 Synthesis ...... 120

xvii

6.2.2 Single Crystal X-Ray Structure ...... 123

6.2.3 Electronic Absorption Studies ...... 127

6.2.4 Electronic Structure Calculations ...... 128

6.2.5 Film Studies ...... 131

6.3 Conclusion ...... 137

6.4 Experimental ...... 137

6.4.1 Synthesis ...... 137

6.2.2 Film Preparation ...... 138

CHAPTER 7 : CRYSTAL ENGINEERING OF Mo2 UNITS THROUGH HALOGEN-

HALOGEN INTERACTIONS ...... 140

7.1 Introduction ...... 140

7.2 Results and Discussion ...... 141

7.2.1 Synthesis ...... 141

7.2.2 Steady State Electronic Spectroscopy ...... 142

7.2.3 Solid State Structures ...... 145

7.2.4 Crystal Packing ...... 150

7.3 Conclusion ...... 155

7.4 Experimental ...... 156

7.4.1 Synthesis ...... 156

xviii

7.4.2 Single Crystal X-Ray Diffraction ...... 158

CHAPTER 8 : FINAL PERSPECTIVES AND FUTURE DIRECTIONS ...... 160

APPENDIX A: SUPPORTING INFORMATION FOR CHAPTER 3 ...... 166

APPENDIX B: SUPPORTING INFORMATION FOR CHAPTER 4 ...... 172

APPENDIX C: SUPPORTING INFORMATION FOR CHAPTER 5 ...... 178

APPENDIX D: SUPPORTING INFORMATION FOR CHAPTER 7 ...... 194

REFERENCES ...... 206

xix

List of Tables

Table 3.1. Select crystallographic parameters for compound 1...... 51

Table 4.1. Experimental shifts of the 1MLCT and 3MoMo* ν(CO) stretches of 2...... 93

Table 4.2. Calculated shifts of the anion and triplet ν(CO) stretches of 2’...... 93

Table 4.3. Select crystallographic information from structure HL and 3...... 98

Table 5.1. GaussView plots of the lowest energy structures of M22Pt – M25Pt4 ...... 107

Table 6.1. Select crystallographic parameters for 1 ...... 125

Table 7.1. Select crystallographic parameters for homoleptic compounds 1 – (F, Cl) .. 147

Table 7.2. Select crystallographic parameters for bis-bis compounds 2 – (F-Cl) ...... 148

Table 7.3. Select crystallographic parameters for bis-bis compounds 2 – (Br - I) ...... 149

●●● Table 7.4. Summary of crystallographic C-X X angles and their respective interactions...... 155

Table A. 1. Select bond lengths (Å) and angles (o) for 1...... 166

Table A. 2. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for 1. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor...... 167

Table B. 1. Select bond lengths (Å) and angles (o) for HL...... 172

Table B. 2. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for HL. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor...... 173

Table B. 3. Select bond lengths (Å) and angles (o) for 3...... 174

Table B. 4. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for HL. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor...... 175

Table C. 1. Selected orbital energy levels for Mo22Pt...... 178

Table C. 2. Selected orbital energy levels for Mo23Pt2...... 179

Table C. 3. Selected orbital energy levels for Mo24Pt3...... 181

Table C. 4. Selected orbital energy levels for Mo25Pt4...... 183

Table C. 5. Selected orbital energy levels for W22Pt...... 187

Table C. 6. Selected orbital energy levels for W23Pt2...... 188

Table C. 7. Selected orbital energy levels for W24Pt3...... 190

Table C. 8. Selected orbital energy levels for W25Pt4...... 192

Table D. 1. Select bond lengths (Å) and angles (o) for 1-F...... 194

Table D. 2. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for 1-F. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor...... 195

Table D. 3. Select bond lengths (Å) and angles (o) for 1-Cl...... 196

Table D. 4. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for 1-Cl. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor. .... 197

Table D. 5. Select bond lengths (Å) and angles (o) for 2-F...... 198

Table D. 6. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for 2-F. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor...... 199

Table D. 7. Select bond lengths (Å) and angles (o) for 2-Cl...... 200

Table D. 8. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for 2-Cl. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor. .... 201

xxi

Table D. 9. Select bond lengths (Å) and angles (o) for 2-Br...... 202

Table D. 10. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for 2-Br. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor. ... 203

Table D. 11. Select bond lengths (Å) and angles (o) for 2-I...... 204

Table D. 12. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for 2-I. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor...... 205

xxii

List of Figures

Figure 1.1. The original refined structure from Harris and coworkers of K2Re2Cl8, which is recognized as the first metal-metal quadruple bond.3 ...... 2

Figure 1.2. Molecular orbital diagram of two square planer d4 metals combining to form a

M2 quadruple bond...... 4

6 Figure 1.3. Proposed structure of Mo2(O2CR)4 complexes before (top) and after

(bottom)7 the discovery of the quadruple bond and subsequent x-ray analysis...... 6

Figure 1.4. A diagram describing how the M2 bond order can change by the removal of electrons from the δ-bonding orbital or the addition of electrons to the higher lying δ*,

π*, and σ* antibonding orbitals...... 7

9 Figure 1.5. GaussView plots of the metal based orbitals of Mo2(O2CH)4 drawn at an isovalue of 0.02...... 8

i i Figure 1.6. Synthesis of M2(T PB)4 starting materials where M2 = M2 or W2 and T PB =

2,4,6-triisopropyl benzoate...... 10

Figure 1.7. Synthesis of Mo2(DAniF)4 where DAniF = N,N’-di-p-anisylformamidinate. 11

i Figure 1.8. A summary of possible reactions with M2(T PB)4 and various stoiciometric additions of carboxylic acids...... 12

Figure 1.9. Frontier molecular orbital diagram involving the interaction of two ligands

10 interacting with a M2 unit to form trans- L–M2–L...... 13

xxiii

Figure 1.10. A frontier molecular orbital diagram (top)13 and a pictorial representation of the out-of-phase and in-phase combinations of the oxylate bridge (bottom).12 ...... 14

i Figure 1.11. UV-Visible spectra of M2(T PB)2(O2CTTh)2 where M2 = Mo2, MoW, or W2 taken at room temperature in THF.15 ...... 16

i Figure 1.12. UV-Visible spectra of Mo2(T PB)2(O2CR)2 where R = Th (red), BTh

(orange), and TTh (yellow).28 ...... 17

Figure 1.13. Jablonski diagram comparing the excited state dynamics of

i 11 M2(T PB)2(O2CTTh)2 where M2 = Mo2, MoW, or W2...... 18

i Figure 1.14. Near-IR emission of Mo2(T PB)2[Re(PMT)(CO)3Cl]2 in 2-MeTHF at 77K,

30 ex = 658 nm...... 19

Figure 1.15. General scheme of a pump probe experiment.31 ...... 20

Figure 1.16. General components of a transient absorption experiment at a given time point.33 ...... 21

Figure 1.17. General schematic of the three types of metal based polymers.34 ...... 22

Figure 1.18. Various Pt-acetylide complexes with band gaps in parentheses.38...... 24

Figure 1.19. Absorption profile of various Pt-acetylide polymers in CH2Cl2 spanning the solar spectrum.38 ...... 25

t t Figure 1.20. ( BuCO2)3M2(O2CCO2)M2(O2C Bu)3 where M2 = Mo2, MoW, W2, the simplest repeating M2 tetracarboxylate unit...... 26

Figure 1.21. Frontier molecular orbital diagram of [(HCO2)2M2(O2CCO2)]n oligomers

49 where M2 = Mo2 (red) and W2 (blue)...... 27

xxiv

Figure 1.22. Photon flux of the AM 1.5 G spectrum (solid) and the calculated accumulated photocurrent (dotted).60...... 29

Figure 1.23. General schematic of a bulk heterojunction solar cell.58 ...... 30

Figure 1.24. Domain formation in BHJ Cells in the case of small molecule/fullerene (left) and polymer/fullerene mixtures (right)...... 31

Figure 1.25. Several examples of π-conjugated organic polymers for use in BHJ Cells as electron donors.58 ...... 32

60 Figure 1.26. General schematic of a TiO2 based dye sensitized solar cell...... 34

Figure 1.27. Absorption profiles of the N3 (red) and N749 (black) dye along with the

57 absorption of TiO2 (blue)...... 35

Figure 1.28. General scheme of Hybrid Type II/III polymers and the tunable range of each components absorption (left) and the proposed coverage of the AM 1.5 G solar spectrum (right)...... 37

i i Figure 3.1. Crystal structure of Mo2(O2CCH3)2[ PrNC(CCFc)N Pr]2 drawn at 50% probability.86 ...... 45

Figure 3.2. The metal-to-carbonyl charge-transfer (MCCT) and metal-to-arene charge- transfer (MACT) transitions present in chromium arene piano stool complexes.100 ...... 46

6 Figure 3.3. fs-TRIR spectrum of MeO2C-C6H5-η -Cr(CO)3 in n-heptane with excitation at

400 nm, by George and coworkers where P = Parent, MA = MACT, MC = MCCT, and

CL = Carbonyl Loss.100 ...... 47

xxv

Figure 3.4 . ORTEP representation of one of the three molecules that crystallized in the asymmetric unit of 1 shown at 50% probability. Hydrogens, solvent and disorder removed for clarity. Mo = Green, Cr = Violet, O = Scarlet, C = Gray...... 50

Figure 3.5. Ground state infrared spectra of 1 (Red) and 2 (Blue) in THF at room temperature...... 52

Figure 3.6. Electronic absorption spectra of compounds 1 and 2 in THF at room temperature...... 53

Figure 3.7. Emission spectra of compound 1 in THF at room temperature...... 55

Figure 3.8. MO diagram of 1’ and 3’ along with select Gaussview plots generated at an isovalue of 0.03...... 56

Figure 3.9. MO diagram of 2’ and 4’ along with select Gaussview plots generated at an isovalue of 0.03...... 57

Figure 3.10. fsTRIR of compound 2 in THF, λex = 675 nm...... 60

Figure 3.11. fsTRIR of compound 1 in CH2Cl2, λex = 514 nm...... 61

Figure 3.12. A pictorial representation of the triplet excited states of 1 and 2 showing holes (red) and electron movement (blue.) ...... 62

Figure 3.13. fsTRIR of compound 1 in THF, λex = 514 nm...... 63

Figure 3.14. fsTRIR of compound 1 in THF with manual stage translation, λex = 514 nm.

...... 64

Figure 4.1. Examples of d6 metal complexes that show 1MLCT transitions...... 69

Figure 4.2. 2-(2-pyridyl)-4-methylthiazol carboxylic acid, PMT-H...... 70

xxvi

Figure 4.3. ORTEP representation of 3 drawn at 50% probability. Disorder, solvent molecules and hydrogens excluded for clarity. Gray = Carbon, Blue = Nitrogen, Scarlet =

Oxygen, Seafoam = Molybdenum...... 74

Figure 4.4. ORTEP representation of HL drawn at 50% probability. Solvent molecules and hydrogens excluded for clarity. Gray = Carbon, Blue = Nitrogen, Scarlet = Oxygen,

Lime = Chlorine, Yellow = Sulfur, Orange = Rhenium...... 75

Figure 4.5. Electronic absorption spectra of HL (black) in MeOH, 1 (red) in THF, and 2

(blue) in THF at room temperature...... 76

Figure 4.6. Electronic absorption spectra of 1 (blue), and 3 (red) in THF at room temperature...... 77

Figure 4.7. Emission (green, ex = 390 nm), excitation (red, em = 650 nm), and absorption (blue) spectra of Re(PMT-H)(CO)3Cl (HL) in MeCN at room temperature. . 78

Figure 4.8. Emission (green, ex = 640 nm), excitation (red, em = 780 nm), and

i absorption (blue) spectra of Mo2(T PB)2[Re(PMT)(CO)3Cl]2 (2) in THF at room temperature...... 79

Figure 4.9. Near-IR emission spectra of 2 in 2-MeTHF at 77K, ex = 658 nm. Average spacing between vibronic features of 359 cm-1, corresponds to Mo-Mo stretch...... 79

Figure 4.10. Ground state infrared spectra of HL (black) and 2 (blue) illustrating the splitting of the ‘A’ and pseudo ‘E’ bands of the Re(CO)3Cl moiety (inset)...... 81

Figure 4.11. GaussView131 representations of the HOMO and LUMO of HL...... 82

Figure 4.12. Frontier molecular orbital energy level diagram of compounds 1’ (red) and

2’ (blue)...... 84

xxvii

Figure 4.13. Select GaussView131 plots of model compound 2’ drawn at isovalue 0.03. 85

+ - Figure 4.14. EPR spectrum of 2 PF6 in THF at room temperature...... 87

Figure 4.15. (a) fs-TA spectra of 2, ex = 675 nm, in THF/DMSO at room temperature (b) fs-TA spectra of 1, ex = 568 nm, in THF at room temperature...... 88

Figure 4.16. (a) ns-TA spectra of 1, ex = 355 nm, in THF at room temperature; (b) kinetic trace at 520 nm gives τ T1 = 73.6 ± 2.8 s...... 89

i Figure 4.17. ns-TA spectra of Mo2(T PB)2[RePMT (CO)3Cl]2 , ex = 355 nm, in THF at room temperature (top). Kinetic trace of transient at 430 nm (left) and 570 nm (right) produced a lifetime () of 21.3 s...... 90

Figure 4.18. Time Resolved Infrared Spectroscopy of HL in THF at room temperature. 91

Figure 4.19. Time Resolved Infrared Spectroscopy of 2 in THF/DMSO at room temperature upon excitation at 675 nm...... 92

Figure 4.20. Time Resolved Infrared Spectroscopy of 1 in THF at room temperature upon excitation at 550 nm...... 95

Figure 5.1. Synthesis and functionalization of a quadruply bonded molybdenum tetracarboxylate with organic and organometallic substituents.134 ...... 101

Figure 5.2. Optimized geometric configurations of Mo22Pt...... 105

Figure 5.3. MO diagram comparing the frontier molecular orbitals of Mo22Pt and W22Pt along with GaussView plots of Mo22Pt...... 108

Figure 5.4. Molecular orbital diagram comparing Mo22Pt, Mo23Pt2, Mo24Pt3, and

Mo25Pt4...... 110

xxviii

Figure 5.5. Molecular orbital diagram comparing W22Pt, W23Pt2, W24Pt3, and

W25Pt4...... 112

Figure 5.6. HOMO (left) and LUMO (right) of Mo22Pt, which is the dominate low energy transition...... 114

Figure 5.7. Various Mo2δ – Lπ* combinations that contribute to the low energy transition in Mo24Pt3...... 115

Figure 5.8. Simulated gas phase UV-Vis spectra of dimolybdenum containing oligomers.

...... 116

Figure 5.9. Simulated gas phase UV-Vis spectra of ditungsten containing oligomers. .. 116

Figure 6.1. Frontier molecular orbital diagram of mixed valent ions of M2 compounds made by metal based oxidation (left)136 and ligand based reduction (right).137 ...... 119

Figure 6.2. The three ligand systems discussed in this Chapter: Isonicotinate (red), isonicotinate N-oxide (green), B(C6F5) adduct of isonicotinate N-oxide (blue)...... 120

Figure 6.3. ORTEP representation of 1 shown at 50% probability. Hydrogens removed for clarity. Mo = Green, N = Blue, O = Scarlet, C = Gray...... 124

Figure 6.4. Extended structure of 1 which propagates parallel to the crystallographic b and c axes. TiPB moieties and solvent removed for clarity...... 127

i Figure 6.5. Electronic absorption spectra of Mo2(T PB)2(nic)2, 1 and 2 in THF at room temperature...... 128

Figure 6.6. GaussView9 plots of the HOMO and LUMO level of 1’drawn at isovalue

0.03...... 130

xxix

Figure 6.7. Frontier molecular orbital diagram comparing Mo2(O2CH)2(nic)2, 1’ and 2’

...... 131

Figure 6.8. The nine metal-oxide films, prior to the dye loading study along with their corresponding thicknesses (Note: Bright white spot on lower left film is from reflection).

...... 133

Figure 6.9. Pictorial representation of the dye loading experiment in a CH2Cl2 solution of

3 (top), and the proposed bonding mode of the dye on a semiconductor surface (bottom).

...... 134

Figure 6.10. Absorption of a 0.02 mM solution of 3 before and after loading onto TiO2

(left) and a picture of the TiO2 film after 12 hours of soaking (right)...... 135

Figure 6.11. Absorption of a 0.02 mM solution of 3 before and after loading onto NiO

(left) and a picture of the NiO film after 12 hours of soaking (right)...... 136

Figure 6.12. Absorption of a 0.02 mM solution of 3 before and after loading onto ITO

(left) and a picture of the ITO film after 12 hours of soaking (right)...... 136

130 Figure 7.1. Molecular ordering by Mo2···O interactions in Mo2(O2C-C6H5)4...... 141

Figure 7.2. Electronic absorption spectrum of families 1-X (Top) and 2-X (Bottom) taken in THF at room temperature...... 143

Figure 7.3. Fluorescence spectra of families 1-X (Top) and 2-X (Bottom) taken in THF at room temperature upon excitation into the MLCT absorption band...... 144

Figure 7.4. ORTEP drawings of 1 (F,Cl) and 2 (F – I) drawn at 50% probability. Solvent and hydrogen atoms removed for clarity...... 146

Figure 7.5. Halogen – Halogen interactions in 1-Cl showing Cl – Cl laddering...... 151

xxx

Figure 7.6. Halogen – Halogen interactions in 2-Br showing a Br – Br slip in the vertical direction...... 152

Figure 7.7. Halogen – Halogen interactions in 2-I showing an I – I slip in the horozontal direction...... 152

Figure 7.8. π – π stacking seen in the crystal packing of 2-F...... 153

Figure 7.9. General form of type 1 and type 2 halogen – halogen interactions...... 154

Figure A. 1. (a) fs-TA spectra of 1 in THF, λex = 515 nm, (inset) kinetic decay at 590 nm; (b) ns-TA spectra of 1 at 100 ns (blue) and 23 μs (red) in THF, λex = 532 nm, (inset) kinetic decay at 470 nm...... 170

Figure A. 2. fs-TA spectra of 2 in THF, λex = 675 nm, (inset) kinetic decay at 495 nm.

...... 171

Figure B. 1. Kinetic traces from fs-TRIR spectra of Re(PMT-H)(CO)3Cl (HL) at (a,b)

-1 -1 i -1 1948 cm and 1844 cm ; and of Mo2(T PB)2[Re(PMT)(CO)3Cl]2 (2) at (c,d) 1879 cm and 1618 cm-1...... 176

Figure B. 2. Kinetic traces from fs-TRIR spectra of Re(PMT-H)(CO)3Cl (HL) at (a,b)

-1 -1 i -1 1948 cm and 1844 cm ; and of Mo2(T PB)2[Re(PMT)(CO)3Cl]2 (2) at (c,d) 1879 cm and 1618 cm-1...... 177

xxxi

List of Schemes

i Scheme 3.1. General synthesis of 1 (M2 = Mo) and 2 (M2 = W) where T PB is 2,4,6- triisopropylbenzoate ...... 48

Scheme 3.2. Synthesis of the organometallic ligand, HL adapted from previous literature.102 ...... 48

Scheme 4.1. Synthesis of HL ...... 71

Scheme 4.2. Synthesis of 1 ...... 71

Scheme 4.3. Synthesis of 2 ...... 72

Scheme 4.4. Synthesis of 3 ...... 72

Scheme 5.1. Proposed synthesis of M2Pt acetylide hybrid polymers where M = Mo or W.

...... 102

Scheme 6.1. Synthesis of compound 1...... 121

Scheme 6.2. Synthesis of compound 2...... 122

Scheme 6.3. Synthesis of compound 3...... 123

17 Scheme 6.4. The first Mo2 dye for DSSC applications...... 132

Scheme 7.1. Synthesis of supported p-halobenzoate Mo2 homoleptic and bis-bis complexes, where X = F, Cl, Br, and I...... 142

xxxii

CHAPTER 1 : INTRODUCTION

1.1 The Metal-Metal Bond

1.1.1 Discovery

The first metal-metal quadruple bond was discovered by an accident of sorts. While

- 2- trying to reduce [ReO4] to make [Re3Cl12] clusters using hydrochloric acid and hypophosphorous acid, Dr. Neil Curtis discovered that a beautiful royal blue solution is formed. After several false assignments to the empirical formula of the compound it was

1 ultimately discovered to be CsReCl4. The rhenium anion that was studied in detail was the potassium salt, KReCl4, as it yielded higher quality crystals for X-Ray diffraction studies.

An initial structure determination by chemists in the Soviet Union erroneously suggested

4- 2 that the anion was actually Re2Cl8 in nature. While the assigned 2+ oxidation state the rhenium of was incorrect, the gross features of the structural analysis were correct. The

- anion contained two virtually square planer ReCl4 fragments combining in an eclipsed fashion to give a remarkably short Re-Re bond distance of 2.22 Å. While enlightening, this initial structure was not without error. The initial report suggested four hydrogen 1 atoms could be found between the chlorines which served to hold the anion together. The structure also suffered from severe twinning which complicated the refinement.

Eventually, Harris and coworkers reported the correct structural solution seen in Figure

1.1, which confirms the initial analysis without invoking “hydrogen atoms” to hold the chlorines together.3

Figure 1.1. The original refined structure from Harris and coworkers of K2Re2Cl8, which is recognized as the first metal-metal quadruple bond.3

After the structural analysis was finalized the conversation turned to explaining the bonding that was occurring in the system. It was obvious that 2.24 Å was a remarkably short metal-metal contact, and some form of metal-metal bonding must be invoked. To this point only one suggestion as to the bonding in the anion had been made by the Soviet chemists in their initial structural report. It was observed that a Re-Re distance of ~2.22

Å was less than that seen in rhenium metal and it was suggested that the valence electrons of rhenium may take part in the formation of a Re-Re bond. They used this description to explain the diamagnetism of the compound.2 2

The idea of a Re-Re quadruple bond stemmed from the fact that the chlorines adopted an eclipsed rather than staggered geometry. This arrangement was not ideal from a steric point of view as there would be considerable repulsion between adjacent chlorines, which implied that there must be another interaction that was overcoming this repulsion energy.

The answer lies in the interaction between the two dxy orbitals that form a δ bond. While the staggered configuration is a few kilocalories lower in energy than the eclipsed configuration, it does not contain the symmetry necessary to form a δ bond. The four metal bonding orbitals, of δ, π, and σ symmetry, can be filled completely in a d8 system,

2- 4 like the Re2Cl8 anion, to form a quadruple bond. A molecular orbital diagram showing these basic orbital combinations can be seen below in Figure 1.2.

Figure 1.2. Molecular orbital diagram of two square planer d4 metals combining to form a

M2 quadruple bond.

The energy of the δ bond was estimated by Gray and coworkers to be worth, at most, 9 –

3- 3- 10 kcal/mol in odd-electron complexes such as Mo2(SO4)4 and Tc2Cl8 , which represents one half of the dissociation energy of the δ bond.5 Since its discovery there have been numerous computational and experimental studies of the nature of the δ bond including, in some small part, this dissertation.1

1.1.2 Mo2 and W2 Paddlewheel Complexes

After these initial reports, the concept of the metal-metal quadruple bond became more widely accepted, leading to the proper structural determination of a host of other compounds including paddlewheel complexes containing Mo2+ and W2+.

In the early 1960’s Wilkinson and coworkers showed that the reaction of Mo(CO)6 with aliphatic carboxylic acids would yield diamagnetic products. At the time this diamagnetism suggested to the authors that the structure consisted of tetrahedrally coordinated Mo2+ centers bridged and chelated by carboxylates.6 See Figure 1.3. To this point no metal-metal bonding was reported, as it was not necessary to explain the experimental data. It was not until the discovery of the metal-metal quadruple bond in

1964, and a structural analysis by Lawton and Mason in 1965 that the true structure of

7 Mo2(O2CCH3)4 was realized. An extremely short Mo-Mo distance of 2.11 Å was found and the assignment of a quadruple bond was used to explain the bonding in the newly discovered paddlewheel complex seen in Figure 1.3.

6 Figure 1.3. Proposed structure of Mo2(O2CR)4 complexes before (top) and after (bottom)7 the discovery of the quadruple bond and subsequent x-ray analysis.

Molybdenum and tungsten in the 2+ oxidation state are particularly interesting because,

2- 4 like the Re2Cl8 anion, each metal has a d arrangement of electrons. This arrangement is necessary for the formation of a quadruple bond as there are enough electrons to completely fill the four bonding orbitals but not enough to begin populating the higher lying antibonding orbitals. The reduction or oxidation of this optimal electronic arrangement can thus cause a decrease in the metal-metal bond order from 4 to 3.5, as seen below in Figure 1.4. Both chemical and photoinduced oxidation of the δ orbital is possible and both will be discussed further in the body of this work.

Figure 1.4. A diagram describing how the M2 bond order can change by the removal of electrons from the δ-bonding orbital or the addition of electrons to the higher lying δ*, π*, and σ* antibonding orbitals.

It has been shown both by calculations and experimental data that the δ orbital is almost entirely metal based and has very little contribution from aliphatic carboxylate ligands

t 8 such as O2C Bu, O2CMe, and O2CH . This can be seen clearly in the DFT calculations of the metal based orbitals in Mo2(O2CH)4, Figure 1.5.

9 Figure 1.5. GaussView plots of the metal based orbitals of Mo2(O2CH)4 drawn at an isovalue of 0.02.

1.1.3 Current Developments in Group 6 Metal-Metal Paddlewheels

M2 bonded compounds where M = Molybdenum are far more abundant than any other metal with well over 1,100 characterized compounds made and more than 550 structurally characterized by x-ray crystallography. Tungsten complexes in contrast are

1 less abundant with <100 W2 compounds structurally characterized. This disparity is due in large part to the difficult synthesis of tungsten starting materials. Over the past decade

8 the Chisholm laboratory has studied molybdenum and tungsten paddlewheel complexes extensively, with particular emphasis on their synthesis, bonding and photophysics.10–13

1.1.4 Synthesis

While there are several viable M2 starting materials the three most utilized in this

i 14 15 dissertation are the tetracaboxylates, M2(T PB)4 (Where M2 = Mo2 or W2 ), and the

16 tetraamidinate, Mo2(DAniF)4.

i Mo2(T PB)4 is perhaps the most straight forward of the three starting materials as all of the components are commercially available and the reaction proceeds in one well defined

i step. To synthesize Mo2(T PB)4, Mo(CO)6 is refluxed in ortho-dichlorobenzene with two equivalents of 2,4,6-triisopropylbenzoic acid, TiPB-H. About 10% of the solvent can be replaced with THF which serves to limit the sublimation of the volatile Mo(CO)6 starting material in two ways: 1) its addition lowers the boiling point of the refluxing solvent which leads to less metal carbonyl forming on the condenser, and 2) the THF boils much more vigorously than the o-dichlorobenzene and thus washes what Mo(CO)6 does sublime back down into the reaction flask. After the solution is refluxed for ~72 hours the

THF is removed under dynamic vacuum and the yellow precipitate that forms is filtered

i and washed with hexanes. Mo2(T PB)4 is a bright yellow, diamagnetic material that is soluble in toluene, THF, and DMSO, and insoluble in hydrocarbons like hexanes.

i i W2(T PB)4 is synthesized by reacting WCl4 with two equivalents of T PB-H. The product

4+ is subsequently reduced to W2 using Na/Hg amalgam. The resulting dark red solid is

i soluble in toluene and THF and insoluble in hexanes. Both M2(T PB)4 starting materials 9

i i are air sensitive with W2(T PB)4 being exceedingly so. The synthesis of both M2(T PB)4 starting materials can be seen below in Figure 1.6.

i i Figure 1.6. Synthesis of M2(T PB)4 starting materials where M2 = M2 or W2 and T PB = 2,4,6-triisopropyl benzoate.

The TiPB moiety was chosen for two reasons: 1) the isopropyl groups on the phenyl ring allows for greater solubility of the starting material in toluene, and 2) the steric bulk of

TiPB causes any subsequent reactions to add in a trans fashion rather than cis, or a complex mixture of the two.

The third starting material utilized in this dissertation is the homoleptic amidinate complex Mo2(DAniF)4 where DAniF = N,N’-di-p-anisylformamidinate. The synthesis of

i this material is similar to that of Mo2(T PB)4 where Mo(CO)6 is refluxed with three equivalents of DAniF-H in o-dichlorobenzene to yield a yellow diamagnetic compound that is soluble in THF. See Figure 1.7. 10

Figure 1.7. Synthesis of Mo2(DAniF)4 where DAniF = N,N’-di-p-anisylformamidinate.

M2 amidinates can be used for several reasons. Amidinates can be used to properly tune the energy of the δ-orbital for a particular application. In addition, M2 complexes chelated by amidinates are kinetically stable and can allow for synthesis of compounds in the cis geometry without the side effect of ligand scrambling which has been seen in carboxylates.17 The synthesis and photophysics of amidinates and their derivatives will be further discussed in Chapter 6.

i M2(T PB)4 starting materials have been shown to be particularly useful in synthesizing new compounds based on the stoichiometric addition of a carboxylic acid. With the

i addition of two equivalents of a monocarboxylic acid to a stirring solution of M2(T PB)4 in toluene it is possible to isolate a bis-bis complex that adopts a trans geometry and a

i 18–20 general formula of M2(T PB)2(O2CR)2. Upon addition of ½ equivalent of a dicarboxylic acid in toluene it is possible to isolate dimers-of-dimers with a general

i i 12 formula of [(T PB)3M2](O2C-R-CO2)[M2(T PB)3]. The addition of one equivalent of a dicarboxylic acid can yield squares,21–23 triangles,24 loops25,26 or other short oligomers

11 based on the chosen acid and M2 starting material. A summary of these basic reactions can be seen below in Figure 1.8.

i Figure 1.8. A summary of possible reactions with M2(T PB)4 and various stoiciometric additions of carboxylic acids.

1.1.5 Bonding

The addition of new π conjugated ligands to form bis-bis complexes or dimers-of-dimers changes the electronic structure of the molecule significantly. In the case of a bis-bis complex the degenerate Lπ and Lπ* orbitals of the two ligands are split when brought into conjugation with the metal d-orbitals.10 The splitting of these ligand based orbitals yields in-phase and out-of-phase combinations in the newly formed molecular orbital with the out-of-phase combination having the proper symmetry to interact with the M2δ- orbital. The splitting between the in- and out-of-phase Lπ orbitals is a rough measure of 12 the coupling between the two ligands. The conjugation caused by ligand overlap with the metal center also serves to stabilize the M2 δ-orbital which is typically the HOMO, however, as this dissertation will describe, that is not always the case. A generalized description of the bonding in bis-bis complexes can be seen below in Figure 1.9.

Figure 1.9. Frontier molecular orbital diagram involving the interaction of two ligands 10 interacting with a M2 unit to form trans- L–M2–L.

In the case of dimers-of-dimers we see a similar set of orbitals. The HOMO and HOMO-

1 of the simple dimer-of-dimers, (HCO2)3M2(O2CCO2)M2(O2CH)3, represent the out-of- phase and in-phase combinations of the oxalate bridge, respectively.12,13 Again, the separation between these two orbitals gives an indication of the electronic coupling between the M2 centers. While this dissertation does not specifically describe the synthesis or characterization of any dimers-of-dimers, there will be considerable

13 discussion of M2 based polymers which will be reminiscent of this bonding motif. A frontier molecular orbital diagram along with a pictorial representation of the out-of- phase and in-phase combinations of the oxylate bridge can be seen below in Figure 1.10.

Figure 1.10. A frontier molecular orbital diagram (top)13 and a pictorial representation of the out-of-phase and in-phase combinations of the oxylate bridge (bottom).12

1.2 Photophysics of Mo2 and W2 Paddlewheel Complexes

While there has been considerable focus over the past 50 years on the synthesis and bonding of M2 quadruple bonds there has also been a great interest in their spectroscopic properties.1

1.2.1 Electronic Spectroscopy

Of the allowable optical transitions in M2 paddlewheels the process that received the most attention initially is the δ  δ* transition. Excitation of an electron from the filled δ

1 1 5 orbital to the empty δ* orbital is an allowed A1g  A2u transition. The reason it is not readily observable in the visible region is due to its low oscillator strength. This is, perhaps, counter intuitive as dipole and spin allowed optical transitions are thought to invariably possess high oscillator strength. This is not the case in δ  δ* optical transitions due to the fact that there is very little overlap between the d-orbitals that form the metal δ-orbital and as the square of the overlap between two orbitals was found by

Mullikan to be proportional to the oscillator strength of the transition it is difficult to see a δδ* absorption.27

In more complex molecules, such as those discussed herein, the δ  δ* transition is not seen as it is masked by other, much more intense, transitions. Chief among these transitions is the metal-to-ligand charge-transfer (MLCT).This transition stems from the fully allowed promotion of an electron from the M2δ orbital to a higher lying Lπ* orbital.

MLCT bands are tunable across the visible/near-IR regions of the electromagnetic

10,11 spectrum by changing the M2 unit and/or changing the ligand. This band can be shifted to lower energy by raising the energy level of the M2δ orbital, lowering the Lπ* 15 orbital or by some combination of both. The energy level of the M2δ orbital is changed by using different combinations of group 6 metals which follows an energetic trend of W2δ

15 > MoWδ > Mo2δ. An example of this tunability can be seen in the UV-Visible spectra

i of M2(T PB)2(O2CTTh)2 where M2 = Mo2, MoW, or W2 and TTh = terthiophene, in

Figure 1.11. Here it is evident that the choice of metal center is capable of shifting the

MLCT band from ~500 nm in the case of Mo2 to nearly 800 nm in the case of W2.

i Figure 1.11. UV-Visible spectra of M2(T PB)2(O2CTTh)2 where M2 = Mo2, MoW, or W2 taken at room temperature in THF.15

The energy of the Lπ* orbitals is determined by two main factors: 1) the degree of π- conjugation and 2) the electronegativity of the ligand’s substituents. By increasing conjugation or adding more electronegative moieties the Lπ* orbital can be stabilized reducing the energy of the MLCT transition. A clear example of increased conjugation

i i can be seen in comparing Mo2(T PB)2(O2CTh)2, Mo2(T PB)2(O2CBTh)2, and 16

i 28 Mo2(T PB)2(O2CTTh)2 where Th = thiophene and BTh = bithiophene. The UV-Visible spectra comparing these three compounds, below in Figure 1.12, shows the red shift in the MLCT band as the ligand is extended from one to three thiophene rings.

i Figure 1.12. UV-Visible spectra of Mo2(T PB)2(O2CR)2 where R = Th (red), BTh (orange), and TTh (yellow).28

1.2.2 Excited State Spectroscopy

M2 tetracaboxylates are typically weakly emissive in the visible region. This emission is due to fluorescence from the 1MLCT excited state back to the ground state. Bis-bis complexes can also undergo intersystem crossing from the S1 state to the T1 state, the character of which is based on the choice of metal and the ligand system. In general it can be said that molybdenum based bis-bis complexes undergo intersystem crossing from

1MLCT states to 3δδ*, while tungsten complexes convert from 1MLCT to 3MLCT

10,29 states. A Jablonski diagram describing the typical excited state dynamics of Mo2,

MoW, and W2 compounds can be seen below in Figure 1.13.

Figure 1.13. Jablonski diagram comparing the excited state dynamics of i 11 M2(T PB)2(O2CTTh)2 where M2 = Mo2, MoW, or W2.

i 3 In the case of Mo2(T PB)2L2 compounds with δδ* states it is possible to see phosphorescence in the near-IR region. These peaks tend to center around 1100 nm and, at liquid nitrogen temperatures in 2-MeTHF glass, show vibrational features with average separation ~350 cm-1 which correlate to the MoMo stretch. An example of this emission can be seen below in Figure 1.14.30

i Figure 1.14. Near-IR emission of Mo2(T PB)2[Re(PMT)(CO)3Cl]2 in 2-MeTHF at 77K, 30 ex = 658 nm.

While it is occasionally possible to assign these excited states through UV-Visible absorption and UV-Vis-NIR emission, some species are more ambiguous and require more advanced spectroscopic techniques like nanosecond (ns) and femtosecond (fs) transient absorption (ns- and fs- TA) and fs- time resolved infrared (fs- TRIR).

1.2.3 Ultra-fast Spectroscopy

To find the excited state life times and dynamics in M2 paddlewheel complexes ultra-fast pump-probe spectroscopy is utilized. In a pump-probe experiment the sample is excited using a pump laser tuned to a particular wavelength. The sample is then probed using broad band white or infrared light at a given time delay. The magnitude of this delay can

19 be varied from femtoseconds to milliseconds depending on the nature of the molecule in question. A general schematic of a pump-probe experiment can be seen below in Figure

1.15.31

Figure 1.15. General scheme of a pump probe experiment.31

The resulting data is a difference spectrum of the ground state absorptions and the newly probed excited state absorptions. These difference spectra are taken at various time points and followed to derive the excited state kinetics. A general scheme of a TA spectrum can be seen below in Figure 1.16. In M2 complexes where M2 = Mo2, fs-TA is used to determine the lifetime of the singlet state which typically lasts from 5 – 20 ps, while ns-

TA is required to determine the triplet state lifetime which typically last for

10,32 microseconds. In the case of M2 = W2, fs-TA can be used to study the singlet excited state, however the triplet state of W2 compounds typically persist for 3 – 10 ns which is longer than the upper limit of the fs-TA instrument and shorter than the lower limit of the ns-TA instrument.

Figure 1.16. General components of a transient absorption experiment at a given time point.33

In order to investigate the character of the singlet and triplet excited states in M2 complexes it is necessary to use a technique that is more sensitive to the electronic distribution in the molecule at a given time delay. fs-TRIR is ideal for this application as the IR stretching frequencies of a molecule are dependent on the electronics. Using fs-

TRIR the electron density can be tracked over time to determine whether the electron ejected from the M2δ orbital is residing on one ligand or both and for what duration this charge separated state exists.

1.3 π-Conjugated Metal Polymers

Conjugated metal polymers are repeating units of π-conjugated organic fragments that interact with metal centers in a particular fashion. Most metal based polymers can be 21 categorized into three basic types. In type I polymers the metals are tethered to the π- conjugated backbone by a linker of some kind. Polymers of this type are attractive because the added degrees of freedom afforded by the tether makes the polymers more soluble in organic solvents. Type II polymers contain a higher degree of metal-backbone bonding, usually through chelation. Type III polymers contain the metal center in the organic backbone itself. A pictorial representation of these polymers can be seen below in

Figure 1.17.34

Figure 1.17. General schematic of the three types of metal based polymers.34

There are many potential applications for metal-based polymers, including light emitting devices, organic electronics and electrochromic windows.35 One exciting application for metal-based polymers is in photovoltaics. Materials containing metal-based polymers could utilize the conjugated metal to harvest light while employing the high charge mobility of the backbone to transport the charge more efficiently to an electrode.36,37

Several metal-based polymers have been investigated in solar cells including platinum

22 based materials.38 Due to their attractive optical properties, metal-based polymers made with M2 repeating units would be ideal for these applications.

1.3.1 Model Compounds

Metal based polymers can be difficult to characterize using conventional techniques such as NMR, MALDI-MS and GPC. This is particularly true for air sensitive materials. In order to understand the optical and structural properties of these polymers it is necessary to first investigate model compounds that are essentially small, isolable, repeating units that represent the final material. Model compounds can be isolated, crystallized and properly analyzed by conventional methods.34 It is also possible to study these small molecules using advanced spectroscopic techniques to better understand their excited state properties which can then be extrapolated to the final polymeric materials.

1.3.2 Pt-Acetylide Polymers

Small molecule and polymeric platinum acetylides have recently been studied in great detail. Raymond Wong and coworkers have made great advances in their synthesis as well as their applicability in photovoltaic cells,38,39 while Kirk Schanze and coworkers have been interested in investigating their photophysical properties.40,41 Pt-acetylide

n polymers are synthesized by reacting PtCl2(P Bu3)2 with a chosen dialkyne and a copper catalyst. The dialkyne is typically a π-conjugated organic that is capable of absorbing

23 large amounts of light. A variety of π-conjugated bridges have been utilized as seen in

Figure 1.18. Further synthetic details will be discussed in Chapter 5 of this work.

Figure 1.18. Various Pt-acetylide complexes with band gaps in parentheses.38

The bonding in Pt-acetylides stems from the interaction of Pt d-orbitals with acetylide p- orbitals which brings the metal center into conjugation with the organic ligand. This increase in conjugation allows for π-electron delocalization and enhanced charge transfer along the polymer.42 The main optical transition in platinum acetylide polymers is a ππ* transition that contains significant Pt character. This band is tunable based on the character of the ligand. Recently, push-pull ligands which contain both a donor and an 24 acceptor have received a good deal of attention. This is due to the added intramolecular charge transfer (ICT) band that appears in these molecules at lower energy than the ππ* transition and allows for better coverage of the solar spectrum.43–45 An example of a Pt- acetylide ππ* and ICT transition can be seen below in the dark blue trace of Figure 1.19 which represents compound 19. Push-pull polymers will be discussed in further detail in the upcoming section describing photovoltaic materials.

Figure 1.19. Absorption profile of various Pt-acetylide polymers in CH2Cl2 spanning the solar spectrum.38

Along with the tunability of their absorption Pt-acetylides have several additional properties that make them interesting candidates for photovoltaics. Due to the enhanced spin-orbit coupling of Pt, intersystem crossing in Pt-acetylides is much more efficient than in organic polymers. This leads to the formation of much longer lived triplet states, which allows for extended diffusion lengths of the charges formed in excitation.46,47 In

n addition platinum based polymers supported by P Bu3 ligands are reasonably soluble in organic solvents and thus easily processable into thin films.38

1.3.3 M2-Oxylate Polymers

The simplest M2 tetracarboxylate repeating unit is the oxalate derivative where two M2 centers are bridged by O2CCO2. See Figure 1.20. Dimers-of-Dimers containing oxalate

12,48 have been well studied and are excellent model compounds for M2 based polymers.

t t Figure 1.20. ( BuCO2)3M2(O2CCO2)M2(O2C Bu)3 where M2 = Mo2, MoW, W2, the simplest repeating M2 tetracarboxylate unit.

Unfortunately, previous attempts to synthesize oxalate based M2 polymers failed to yield a material of any considerable molecular weight. Computational analysis of M2 oxalate polymers however allow for better understanding of M2 polymers with more complex ligand architecture. The theoretical study of [(HCO2)2M2(O2CCO2)]n oligomers where M2

= Mo2 and W2 and n = 1 – 5 yielded several interesting conclusions: 1) After four repeating units there is only a nominal change to the energy levels of the metal based

HOMO and the Lπ* based LUMO indicating that the λmax of an oligomer containing four units will occur at virtually the same energy as one with more than five repeating units.

This finding was confirmed with TD-DFT calculations. 2) As more repeating units are added there are more combinations of the M2δ orbitals and oxalate π* orbitals. These various combinations form a broad band of orbitals. If this trend is extrapolated to ∞ it is estimated that the width of the δ-band would be >1.0 eV in the case of tungsten and ~0.8 eV for molybdenum. 3) If the polymer were to be oxidized there would be good hole transport along the chain. Similarly a reduction would lead to an electron being placed in the Lπ* based band which would allow for electron transport along the chain.49 A frontier molecular orbital diagram for the oligomers can be seen below in Figure 1.21.

Figure 1.21. Frontier molecular orbital diagram of [(HCO2)2M2(O2CCO2)]n oligomers 49 where M2 = Mo2 (red) and W2 (blue).

1.4 Photovoltaic Cells

With the discovery of the photoelectric effect by Edmond Becquerel in 1839 came the goal of converting light into usable energy.50,51 In order to harness this energy many generations of solar cells have been made with varying degrees of success and efficiency.

Today it is possible to place the majority of solar cells into three main categories: 1) Solid state cells that utilize semiconductors like Si52, GaAs,53,54 or CIGS.55,56 While cells that fall into this category are some of the most efficient they are also the most costly to produce. 2) Dye Sensitized Solar Cells (DSSCs) consisting of organic or inorganic dyes tethered to nanoparticles. The dye absorbs the light and the ejected electron is transferred to the nanoparticles to create a current.57 3) Bulk Heterojunction (BHJ) Cells consisting of a light absorbing electron donating material, which is typically a polymer, and an electron accepting material.58 There are tradeoffs in each type of solar cell. Those with the highest efficiency tend to be difficult to process in large amounts or are expensive to make. Those cells that are easy to fabricate in large amounts using inexpensive material are typically not efficient enough to be useful. In order to have a useful solar cell we must solve the problem of efficiency while also creating an affordable and easily processable material. Regardless of the type of solar cell, in order to be efficient it must absorb a large amount of the solar spectrum which ranges from 300 nm to well over 1200 nm.57–59 See

Figure 1.22. This can be synthetically challenging when designing a material, as there needs to be enough allowable optical transitions to yield an absorption profile that covers such a broad area. 28

Figure 1.22. Photon flux of the AM 1.5 G spectrum (solid) and the calculated accumulated photocurrent (dotted).60

Of these three categories of solar cells, solid state semiconducting cells fall out of the scope of this work. Bulk heterojunction solar cells and dye sensitized solar cells, however, will both be discussed in this dissertation as possible applications of M2 paddlewheels.

1.4.1 Bulk Heterojunction Cells

Bulk heterojunction (BHJ) cells are promising materials due to their low cost, versatility, flexibility and ease of processing. Organic cells of this kind consist of two interpenetrating compounds, a donor and an acceptor, that form contiguous channels from the cathode to the anode. The donor material is typically a π-conjugated polymer that is capable of absorbing sun light. The length of the polymer causes the energy levels

29 to be closely spaced which allows for the formation of a band structure.58 When excited by light an exciton, or electron-hole pair, is formed. In the absence of any other material the exciton will simply recombine, but in the presence of an electron acceptor it is possible to see charge transfer from the donor to the acceptor. Electron accepting materials are less diverse than electron donating materials and are typically fullerene derivatives like phenyl-C61-butyric acid methyl ester (PCBM) or C70. Once the charge has been transferred from a donor to an acceptor it can migrate along the channels formed in the BHJ morphology, with holes migrating through the polymer and electrons flowing through the fullerene acceptor.61,62 A general scheme of a BHJ cell can be seen below in

Figure 1.23.

Figure 1.23. General schematic of a bulk heterojunction solar cell.58

The interconnected BHJ morphology is crucial as it allows for more Donor-Acceptor contact than a simple bilayer design, and thus more efficient charge separation of the electron-hole pair. Bilayer devices and BHJs that contain large domains lose a great deal of efficiency due to exciton recombination as the electron is too far away from the accepting material to adequately diffuse.58 There have been many studies exploring the structure-property relationships of various materials and how they influence film formation.63–65 In general it can be said that small molecules tend to form large domains due to their tendency to crystallize, while polymers tend to form smaller domains and channels from one electrode to the other. For this reason most BHJ cells are made with polymers rather than small molecules. A pictorial representation of the general morphology found in small molecule and polymer based BHJ cells can be seen below in

Figure1.24.

Figure 1.24. Domain formation in BHJ Cells in the case of small molecule/fullerene (left) and polymer/fullerene mixtures (right).

Due to the availability of aromatic starting materials and the ubiquity of carbon-carbon cross-coupling reactions many diverse π-conjugated organic polymers have been synthesized. A handful of these polymers can be seen below in Figure 1.25.

Figure 1.25. Several examples of π-conjugated organic polymers for use in BHJ Cells as electron donors.58

The standard by which new BHJ cells are measured is a cell composed of poly-3- hexylthiophene, P3HT, and PCBM. These devices tend to have a maximum efficiency of

~5%. This efficiency is due in large part to P3HT’s relatively large band gap that cannot utilize the low energy light of the solar spectrum.66 To combat this, different aromatic groups have been used to synthesize low band gap donor materials, many of which can be seen in Figure 1.25. Another technique used in modern material design, which has been discussed previously, is the implementation of polymers that contain push-pull repeating 32 units which serve to lower the band gap drastically.66,67 One example of this can be seen in poly(9,9’-dioctylfluorene-co-bis-N,N’-(4-butylphenyl)- bis-N,N’-phenyl- 1,4- phenylenediamine), PFB which has an electron rich phenylamine moiety and an electron deficient fluorene moiety.68

1.4.2 Dye Sensitized Solar Cells

The first dye sensitized solar cell (DSSC) was reported in 1991 by O’Regan and

Grӓtzel.69 DSSCs allow for design of solar cells with different colors and transparencies while offering low cost alternatives to traditional semiconductor materials. They are remarkably stable at elevated temperatures, maintaining the majority of their efficiency after 1000 hours at 80 oC.60 All of these benefits make DSSCs attractive candidates for solar applications that require a certain amount of aesthetic appeal such as building materials.

The basic design of a DSSC involves dye molecules anchored to TiO2 nanoparticles which are in turn deposited on an electrode. This film is then covered in an electrolyte containing a redox active molecule such as I-. The cell is then sealed with a transparent electrode. The current is produced when light ejects an electron from the dye molecule

- - - into the TiO2, the dye is then reduced by the I to form I3 , and the I3 is subsequently reduced by the counter electrode back to I-, completing the circuit. A general schematic of a TiO2 based DSSC can be seen below in Figure 1.26.

60 Figure 1.26. General schematic of a TiO2 based dye sensitized solar cell.

While it is possible to change many different aspects of a DSSC such as the semiconductor and the electrolyte, the dye is the most versatile. Similarly to other photon harvesting materials discussed previously, dyes must absorb as much of the solar spectrum as possible to increase efficiency. The standard dye DSSCs are measured against, P3HT’s DSSC counterpart, is the N3 dye. N3 is a ruthenium thiocyanate chelated by two 4,4’-COOH-2,2’-bipyridine ligands and has an absorption profile that is reasonably broad, stretching from 400 nm to around 750 nm (red trace in Figure 1.26).

N3 is anchored to the TiO2 nanoparticles by the carboxylic acids on the bipyridyl ligands.57 When the dye absorbs light, the lowest energy transition is an MLCT from the

Ru to the bpy ligands which facilitates electron injection. The hole that remains on the dye resides on the metal and the NCS ligands. Another dye in this family is the black dye

N749, which replaces the bipyridyl ligands with a terpyridyl ligand, and absorbs light 34 from 400 nm to 900 nm. The absorption profiles of the N3 and N749 dye can be seen below in Figure 1.27.

Figure 1.27. Absorption profiles of the N3 (red) and N749 (black) dye along with the 57 absorption of TiO2 (blue).

While the amount of light the dye absorbs is important, how well the dye is anchored to the TiO2 is also vital. In the case of N3 and N749 the anchoring group is -CO2H which is quite common, as carboxylic acids allow for stable, bidentate, interactions with the nanoparticle surface.57,60 Several other anchoring groups have been shown to be effective such as, esters, acetic anhydrides, amides, sulfonates and silanes.60,70 There are several different anchoring modes seen in DSSCs: 1) covalent attachment, 2) electrostatic interactions, 3) hydrogen bonding, 4) physisorption, and 5) physical entrapment.60 Of 35 these modes covalent attachment tends to lead to more stable dyes with higher quantum yields of electron injection.71–73 A new kind of anchoring group will be discussed in

Chapter 6 of this dissertation.

1.5 Statement of Purpose

The goal of this dissertation is to investigate how M2 paddlewheel complexes interact with other metals. While interactions between M2 metal centers and organic ligands have been studied in detail,1 there have been very few details reported on how organometallic or metal-organic ligands influence metal-metal bonding and photophysics. As such, new ligands containing transition metals like chromium and rhenium have been synthesized to react with M2 moieties to investigate the influence of added d-orbitals on the photophysical properties of the system. The interactions of M2 units with solid state surfaces as well as halogens will also be discussed in later chapters.

1.5.1 Hybrid Type II/III Metal Polymers

The addition of metal containing ligands to M2 systems is attractive because it allows for additional allowable optical transitions as compounds containing Cr and Re possess

MLCT transitions of their own. By tethering a photoactive secondary metal to the M2 core we add another level of tunability to the system which can be used to cover more of the solar spectrum. A M2 polymer that is linked together by metal containing ligands could be considered a hybrid type II/III metal polymer that is capable of absorbing high

36 energy photons with the π-conjugated backbone, intermediate energy light with the organometallic MLCT, and low energy light with the M2  ligand MLCT. A general scheme describing this hybrid system can be seen below in Figure 1.28 along with the proposed coverage of the solar spectrum.

Figure 1.28. General scheme of Hybrid Type II/III polymers and the tunable range of each components absorption (left) and the proposed coverage of the AM 1.5 G solar spectrum (right).

Model complexes made to study these proposed polymers will also shed light on the nature of the metal-metal bond and mixed metal systems. Chapters 3 and 4 of this work will elaborate on this concept.

1.5.2 Chapter Summary

Chapter 3 describes the synthesis and characterization of the M2 paddlewheel compounds

i 6 M2(T PB)2[O2C-C6H5-η -Cr(CO)3]2 where M2 = Mo2 or W2. This is a proof-of-concept that organometallic ligands and M2 quadruple bonds can coexist to make a stable final product. The choice of Cr(CO)3 was a conscious one because the carbonyl stretches are easy to track using fs-TRIR. 37

Chapter 4 explores the synthesis of another metal carbonyl compound, namely

i Mo2(T PB)2[PMTRe(CO)3Cl]2, and describes how the ReCl(CO)3 moiety influences the photophysics of the Mo2 metal center. The new rhenium based ligand, PMTRe(CO)3Cl, is also analyzed as an affordable analog of HO2C-bpyRe(CO)3Cl.

Chapter 5 is primarily a computational study describing the electronic structure of M2-Pt acetylide polymers. The frontier molecular orbital diagrams are constructed of models containing 2 to 5 repeating units to better understand the properties of mixed metal polymers. The optical spectra are also predicted using TD-DFT which could be helpful when analyzing M2-Pt polymers in the future.

i + - Chapter 6 discusses the synthesis of trans-Mo2(T PB)2(O2CC5H4N -p-O )2 and cis-

+ - Mo2(DAniF)2(O2CC5H4N -p-O )2. The optical and theoretical properties of these molecules are explored and the influence of the N-oxide moiety is compared to previously discovered pyridine complexes. Additionally, their interactions with Lewis acids such as B(C6F5)3 and various films consisting of TiO2, NiO, and ITO are investigated. Initial results suggest pyridyl N-oxides could be a new anchoring group for

DSSCs.

Chapter 7 focuses on the crystal structures of six halobenzoate Mo2 paddlewheel complexes. The halogen-halogen interactions found to exist in the crystal structures of these compounds suggests that ligands of this type can be used in crystal engineering of materials in the future. The two types of halogen bonding seen in these structures will be discussed and analyzed.

CHAPTER 2 : MATERIALS AND METHODS

2.1 General Experimental

All reactions were performed under 1 atm of UHP argon using standard Schlenk or glovebox techniques. Chemicals were purchased from Sigma Aldrich Co. and used without further purification. Manipulations of the studied compounds were performed under nitrogen inside a glovebox or under argon on a Schlenk line. Solvents were dried and distilled from the appropriate drying agents and then degassed prior to use. Solvents were stored over 4Å molecular sieves in flasks with Kontes tops.

NMR spectra were recorded on a 400 MHz Bruker DPX Advance 400 spectrometer. All

1H NMR chemical shifts are in parts per million (ppm) relative to the protio impurity in

DMSO-d6 at 2.50 ppm, THF-d8 at 1.73 ppm, , or CDCl3 7.24 ppm. The solvent employed will be designated in the experimental section of each chapter.

Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra were obtained on a Bruker Microflex mass spectrometer. Dithranol was used as the matrix. Samples were prepared by adding a solution of the matrix to the solid sample.

This was then spotted on the plate for analysis.

2.2. Steady-state spectroscopy

Steady-state electronic absorption and UV–visible emission measurements were carried out with 1.0 × 1.0 cm quartz cuvettes equipped with Kontes stopcocks. Electronic absorption spectra at room temperature were recorded using a Perkin-Elmer Lambda 900 spectrometer in solution.

Fluorescence measurements were made on a SPEX Fluoromax-2 spectrofluorometer in the UV–visible region in THF solution. Emission measurements in the near-infrared region were performed in J. Young NMR tubes at room temperature and 77 K in 2- methyl THF. Spectra were recorded on a home-built instrument equipped with a germanium detector. Samples were irradiated into their MLCT bands. On the NIR setup, this was done with either 405 nm or 658 nm excitation. Samples were prepared with an absorbance of < 0.3.

Ground state infrared spectra were obtained with a Perkin-Elmer Spectrum GX. Samples were sealed in a Perkin-Elmer rectangular semidemountable cell with a 0.1 mm Teflon spacer between a 4 and a 2 mm CaF2 window. The spectra were baseline-corrected, and the background solvent spectrum was subtracted.

2.3. Transient absorption spectroscopy

Nanosecond TA was performed on samples in 1 × 1 cm square quartz cuvettes with

Kontes stopcocks. Measurements were made on a home-built instrument pumped by a

40 frequency-doubled (532 nm) or frequency tripled (355 nm) Spectra-Physics GCR-150

Nd:YAG laser (fwhm ≈ 8 ns, ~5 mJ/pulse). The power at the sample was set to 100 mW

Signal from a Hamamatsu R928 photomultiplier tube was processed with a Tektronics

400 MHz oscilloscope (TDS 380).

Nanosecond transient absorption spectroscopy was expertly performed by Dr. Thomas F.

Spilker.

Femtosecond transient absorption experiments were performed with a Ti:sapphire and regenerative amplifier combination (1 kHz, 300 fs full width at half-maximum) that has been previously described.74 Samples were prepared with absorbances of ~0.3–0.8 in a

1.0 mm quartz cuvette with Kontes top. Excitation power at the sample was 1–2 μJ.

Spectra collected underwent wavelength calibration and group velocity dispersion corrections.

In general, kinetics were fit to a sum of exponential decay terms, S(t) = Σi Ai exp(−1/τi) +

C, using Igor Pro 6.0 or SigmaPlot 12.0, where Ai is the amplitude, τ is the lifetime, and

C is an offset. Error bars for the lifetimes are reported as standard errors of the exponential fits.

Femtosecond transient absorption spectroscopy was expertly performed by Dr. Samantha

E. Brown-Xu.

2.4. Time-Resolved Infrared Spectroscopy

Time-resolved infrared experiments were performed using a Ti:sapphire oscillator/regenerative amplifier combination (1 kHz, fwhm ≈ 300 fs). Briefly, the 800 41 nm fundamental is split to produce both UV/visible pump pulses and mid-IR (2 – 10 μm) probe pulses. The pump pulses are generated from an OPA with either a SHG or SFG attachment, providing tunability through the visible region, while probe pulses arise from an OPA with a difference frequency generation (DFG) attachment. The mid-IR pulses are split into a probe and reference beam with a Ge beamsplitter and then pass through the sample where the pump beam is overlapped with the probe. Synchronization of pump and probe is achieved by chopping the pump beam at a frequency of 500 Hz, enabling the probe signal to be measured under pump on/off conditions. Probe and reference signals are detected by a Triax 320 spectrometer containing two 32 element HgCdTe arrays cooled by lN2. Overall signal is obtained following subtraction of the reference signal.

Sample solutions were prepared in a glovebox using THF as the solvent and sealed in a

Perkin-Elmer semidemountable cell with a 0.1 mm Teflon spacer between a 4 and 2 mm

CaF2 window. Sample concentrations were such that the absorbance at the MLCT λmax was 0.5–1.5. Both compounds were excited at the reported wavelength with the power at the sample of 1 μJ. Samples were placed on a motorized Z stage and translated during the experiment to prevent photodecomposition. Spectra were obtained over a wide range of

IR wavelengths by collecting multiple probe regions of ~100 cm–1 each. Igor Pro 6.3 was used to plot the spectra and analyze kinetic data. Lifetimes were determined by fitting the kinetics to a sum of exponentials, f(x) = Σi Ai exp(−x/τi) + C.

Femtosecond TRIR data was collected and formatted by Dr. Samantha E. Brown-Xu.

2.5. Computational Methods

Unless otherwise noted computations were employed as follows. Model complexes were optimized in the gas-phase using density functional theory (DFT) utilizing the

Gaussian09 suite of programs.75 The B3LYP76,77 functional was used in conjunction with the SDD basis set78 and energy consistent pseudopotentials for Mo, W, Cr, Pt, and Re and the 6-31G* basis set for all other atoms.79 Vibrational frequency analysis was used to confirm that the optimized structures were minima on the potential energy surface.

GaussView9 plots are shown with an isovalue of 0.03

CHAPTER 3 : THE EFFECT OF Cr(CO)3 PIANO STOOL LIGANDS ON THE M2

CORE: SYNTHESIS, CHARACTERIZATION AND PHOTOPHYSICS

Adapted from a 2012 publication in the Journal of the American Chemical Society82

3.1 Introduction

While most spectroscopic studies of M2 quadruple bonds initially focused on the δδ* optical transition and its emission,8 recent publications have been interested primarily in

1 the M2δ to ligand π* transition. This singlet metal-to-ligand charge-transfer ( MLCT) state has been shown to have remarkably long lifetimes for a heavy metal complex and can intersystem cross to a triplet state that is either 3MLCT or 3MMδδ* in nature.83,84 To track the electronic distribution in the S1 and T1 excited states with fs-TRIR, molecules with IR active reporting groups must be incorporated. Reporter groups such as C≡N and

C≡C have been used effectively in the past to determine whether charge was delocalized or localized in the MLCT states based on the magnitude of the shift.85

These studies have lead to a wealth of knowledge about the photophysical properties of organic ligands bound to M2 units. However, there have been very few studies to this point investigating the excited state dynamics of secondary transition metal units attached to M2 moieties. One study that touched upon the incorporation of metal-based ligands

44 described the synthesis of a ferrocene (Fc) based Mo2 amidinate complex (Figure 3.1), however no excited state dynamics are reported.86

i i Figure 3.1. Crystal structure of Mo2(O2CCH3)2[ PrNC(CCFc)N Pr]2 drawn at 50% probability.86

The metal based ligand discussed in this chapter is the chromium tricarbonyl piano stool

6 complex, O2C-C6H5-η -Cr(CO)3. A metal carbonyl is an excellent candidate for this application due to the CO stretch. Carbonyl stretching frequencies are isolated from other

IR stretches, they have high oscillator strengths, and they are highly sensitive to electronic perturbations of the metal. In addition, the chromium d-orbitals have the ability to mix with the M2δ orbital which may alter the photophysical properties of the overall molecule.

Many compounds containing chromium, rhenium and molybdenum have been studied by ultra-fast spectroscopy to investigate their reactivity with light, including isomerization, charge transfer and ligand loss.87–97 George and coworkers have been particularly interested in chromium piano stool complexes, and have found that in many cases upon irradiation into the metal-to-arene charge-transfer band, a CO ligand will dissociate from 45 the metal center. 98–101 Using fs-TRIR George was able to follow two metal based transitions, the metal-to-arene charge-transfer (MACT) and the metal-to-carbonyl charge- transfer (MCCT), by observing their respective CO stretches.100 Figure 3.2 summarizes the excited state CO stretching frequencies that correlate to these transitions.

Figure 3.2. The metal-to-carbonyl charge-transfer (MCCT) and metal-to-arene charge- transfer (MACT) transitions present in chromium arene piano stool complexes.100

It should be noted that electronic donation to the carbonyl ligands from the chromium

(MCCT) causes a ~17 cm-1 shift to lower energy from the parent compound, as the electron populates a CO π* orbital. The opposite is true in the case of MACT where a

~17 cm-1 shift to higher energy is seen due to a removal of an electron from the chromium metal center thus reducing the effect of Cr dπ to COπ* back bonding. These transient features can be seen below in Figure 3.3.

6 Figure 3.3. fs-TRIR spectrum of MeO2C-C6H5-η -Cr(CO)3 in n-heptane with excitation at 400 nm, by George and coworkers where P = Parent, MA = MACT, MC = MCCT, and CL = Carbonyl Loss.100

These in depth studies allow for an excellent point of reference for investigating how

Cr(CO)3 moieties influence M2δ to ligand charge-transfer. As such the synthesis, characterization and photophysics of two new complexes will be discussed in this chapter as an initial study of how secondary metals influence the electronics in M2 systems.

3.2 Results and Discussion

3.2.1 Synthesis

i 6 Compounds of the form M2(T PB)2[O2C-C6H5-η -Cr(CO)3]2 where M2 = Mo2 (1) or W2

6 (2) were synthesized by stirring two equivalents of the chromium ligand, HO2C-C6H5-η -

i Cr(CO)3 (HL) with one equivalent of M2(T PB)4 in a 3:1 mixture of THF/Et2O for three days. See Scheme 3.1.

i Scheme 3.1. General synthesis of 1 (M2 = Mo) and 2 (M2 = W) where T PB is 2,4,6- triisopropylbenzoate

After three days the formerly yellow, 1, and red, 2, solutions turned red and blue respectively. The solvent was reduced in vacuo yielding red and blue precipitates which were washed once with toluene and three times with hexanes. The remaining solid was dried and stored under argon. The new compounds are soluble in THF, CH2Cl2, DMSO and CH3CN and slightly soluble in toluene and benzene. X-Ray quality crystals were grown of 1 through slow cooling of a concentrated benzene solution.

The organometallic ligand HL was synthesized from a modified literature procedure making sure to exclude oxygen at all synthetic steps.102 See scheme 3.2. This ligand and its methoxy intermediate are relatively stable in the presence of oxygen at low temperatures but will decompose rapidly to yield a green solution if exposed to air at high temperatures.

Scheme 3.2. Synthesis of the organometallic ligand, HL adapted from previous literature.102

3.2.2 Single Crystal X-Ray Structure

Orange single crystals of 1 were isolated from a concentrated solution of benzene and were air sensitive. Compound 1 crystallized in the triclinic space group P-1 which contained three molecules in the asymmetric unit along with several highly disordered benzene molecules. A center of inversion was found in the middle of each molecular Mo-

Mo bond. The Mo2(O2C-R)4 core is unremarkable and consistent with other Mo2 paddlewheel complexes with Mo-Mo, and Mo-O bond distances ~2.1 Å. It should be noted that there is no solvent coordinated axially along the Mo-Mo bond and there is no apparent laddering of molecules which has been seen previously.1

The TiPB moieties are significantly twisted out of conjugation with respect to their attending O2C units, effectively removing their electronic communication with the Mo2

6 o core. The C6H5-η -Cr(CO)3 ligand twists no more than 4 out of planarity with its O2C

103 unit which allows for extensive Lπ - Mo2δ - Lπ conjugation. The Cr···C6 centroid

104 distance is 1.70 Å on average which is typical for arene-Cr(CO)3 distances. A table of selected crystallographic parameters can be seen in Table 3.1 and an ORTEP representation of 1 can be seen in Figure 3.4.

Compound 1 Chemical Formula C234H264Cr6Mo6O42 Formula Weight 4617.95 Temperature (K) 150(2) Space Group Triclinic, P-1 a (Å) 16.1117(3) b (Å) 19.3001(3) c (Å) 20.2389(3)  (o) 61.8080(14) β (o) 81.3167(7)  (o) 81.9714(7) V (Å3) 5466.37(17) Z 1 Dcalcd (Mg/m3) 1.403 Crystal Size (mm) 0.38 X 0.35 X 0.23 Theta range for data collection 2.01 to 22.46o ,(Mo, K) (mm-1) 0.690 Reflections collected 45260 Unique reflections 14136 [R(int)= 0.0443] Completeness to theta (22.46o) 99.4% Data/restraints/parameters 14136 / 54 / 1282 R1a (%) (all data) 7.61 (10.31) 16.12 (17.63) wR2b(%)(all data) Goodness-of-fit on F2 1.148 Largest diff. peak and hole (e Å-3) 1.275 and -0.823

aR1 =  | |Fo|-|Fc| | /  |Fo| 2 2 2 2 2 1/2 bwR2 = {  [w( Fo -Fc ) ] /  [ w(Fo ) ] }

Table 3.1. Select crystallographic parameters for compound 1.

3.2.3 Ground-State Infrared Spectroscopy

The new compounds show characteristic ν(CO) infrared stretches arising from the

6 Cr(CO)3 ligand. The O2CC6H5-η -Cr(CO)3 ligand has a pseudo C3v symmetry which has 51

-1 two IR-active bands, namely the ‘A’ and ‘E’ bands at 1977 and 1908 cm for 1 and 1971 and 1903 cm-1 for 2. See Figure 3.5.

Figure 3.5. Ground state infrared spectra of 1 (Red) and 2 (Blue) in THF at room temperature.

-1 The energy of these absorptions are red shifted by ~20 cm compared to the parent

6 chromium tricarbonyl benzoate ester, MeO2CC6H5-η -Cr(CO)3, which can be seen at

1992 and 1929 cm-1. This is due to more carbonyl π* backbonding from to the chromium t2g orbitals, which is caused by the concurrent M2δ to benzoate CO2 π* backbonding.

3.2.4 Electronic Absorption Spectra

The electronic absorption spectra of 1 and 2 in THF at room temperature are shown in

Figure 3.6. Solutions of 1 and 2 give an intense red or blue color respectively which arise

1 1 from a fully allowed MLCT transition from the M2δ to benzoate π*. This MLCT transition manifests as a peak at ~475 nm (1) or ~675 nm (2). In the case of the tungsten

i compound 2 we also see a peak near 400 nm which corresponds to the W2δ to O2C-T PB

1 π* MLCT transition. The analogous transition in 1 is masked by the Cr t2g to π* transition at ~315 nm.

Figure 3.6. Electronic absorption spectra of compounds 1 and 2 in THF at room temperature.

This observed electronic absorption spectra is in good agreement with the spectra calculated using TD-DFT for the case of molybdenum, vida infra. The calculations for the tungsten complex, while in qualitative agreement with the observed spectrum, 53 estimate the 1MLCT transition to be higher in energy. This is likely due to the greater spin-orbit coupling in 5d metals which calculations do not accommodate for appropriately. It is important to note that the calculated spectra are in agreement with that of the experimental despite the use of model complexes where formate is substituted for

TiPB.

3.2.5 Luminescence Studies

Compound 1 shows emission from the S1 state at 625 nm and phosphorescence from its

T1 state at ~1100 nm which additionally shows vibronic features that correlate to the

MoMo stretch of ~400 cm-1. See Figure 3.7. This is consistent with the assignment of a

84 MoMoδδ* triplet state which has been seen in numerous Mo2(O2CR)4 complexes.

Compound 2 showed weak fluorescence but was unfortunately at the edge of the limit of our spectrometer at ~900 nm. There was no detectible phosphorescence observed, which indicates a triplet state that undergoes nonradiative decay to the ground state.

Figure 3.7. Emission spectra of compound 1 in THF at room temperature.

3.2.6 Computational Studies

In order to better understand and interpret spectroscopic data, density functional theory calculations and time-dependent density functional calculations on model compounds were employed. The model complexes were derived from the previously described structural information. Due to the twisting of the TiPB moiety out of conjugation with the

M2 unit it is assumed that the phenyl group will have little influence on the electronic structure and was therefore replaced with formate. This assumption saves on computational resources by allowing for idealized symmetry and reduces the number of degrees of freedom in the molecule. The model compounds of 1 and 2 are 1’ and 2’

55 respectively. In addition these models are compared to their benzoate counterparts,

M2(O2CH)2(O2C-Ph)2 where M2 = Mo2 (3’) or W2 (4’), to investigate the effects of the -

Cr(CO)3 fragment.

The MO diagram for 1’ and 3’ can be seen in Figure 3.8 along with Gaussview9 plots of the HOMO, LUMO and LUMO+1 levels of 1’. The stabilizing influence of the Cr(CO)3 unit is immediately apparent. The organometallic fragment stabilizes the HOMO by ~0.3 eV while also significantly lowering the ligand-based π* orbitals, which are primarily in- and out-of-phase benzoate π* in character with a small contribution from Cr d-orbitals.

See Figure 3.8.

Figure 3.8. MO diagram of 1’ and 3’ along with select Gaussview plots generated at an isovalue of 0.03. 56

For 1’ the LUMO is the Mo2δ* orbital, while the LUMO and LUMO+1 of 2’ are the in- and out-of-phase Lπ* orbitals. See Figure 3.9. This is typical of Mo2 and W2 complexes due to the W2δ lying ~0.5 eV higher in energy than its Mo2δ counterpart. The general trends when comparing 1’ to 3’ are similar when considering 2’ and 4’. Again, we see the stabilizing effect of the Cr(CO)3 unit on the Lπ* and W2δ orbitals leading to a HOMO-

LUMO gap nearly 0.3 eV smaller in the case of the organometallic ligand.

Figure 3.9. MO diagram of 2’ and 4’ along with select Gaussview plots generated at an isovalue of 0.03.

The TD-DFT calculations on 1’ predict the lowest energy transition to be primarily

HOMO  LUMO+1 in character. However, it is important to note that this transition is not purely Mo2δ  Lπ* in character, as there is a significant contribution of Crdπ  benzoate π* character. For 2’ however, the lowest energy transition is solely HOMO 

LUMO and shows no overlapping contribution from Crdπ orbitals.

3.2.7 Time-Resolved Studies

In order to better understand the character of their excited states, both 1 and 2 were examined by UV-visible transient absorption (TA) and time-resolved infrared (TRIR).

TA allows for determination of the singlet and triplet lifetimes, while TRIR helps to elucidate the character of these states by observing the dynamics of specific stretches. In the case of 1 and 2 carbonyl moieties are particularly attractive for TRIR for several reasons: 1) CO has a high oscillator strength, 2) the stretching frequency of CO is well separated from other IR active stretches (2100 – 1900 cm-1) and 3) CO stretches are highly sensitive to electronic perturbation.

Using ns and fs TA the S1 and T1 excited state lifetimes can be determined by the kinetic data. For molybdenum the S1 and T1 lifetimes were found to be 18 ps and 24 μs in

CH2Cl2 and THF respectively. The analogous lifetimes for tungsten are 1.5 ps for S1 and between 2 and 10 ns for T1. These lifetimes are comparable to other M2-carboxylate compounds although it should be noted that the S1 state of 1 is slightly longer than normal.85 ns- and fs- TA traces can be seen in the appendix.

Ultimately, the purpose of studying these compounds with TRIR is to examine the charge delocalization during the excited state and the role the secondary chromium metal plays.

6 While much work has been done on Cr(CO)3 complexes such as MeO2CC6H5-η -

100 Cr(CO)3 , little is known of their effect on chromophores like M2-carboxylates. The analysis of 1 was not straightforward so it is perhaps prudent to begin with the more well behaved tungsten complex 2.

Photoexcitation of 2 at 675 nm in THF gave the spectra shown in Figure 3.10. The spectra show ground state bleaches at 1970 and 1900 cm-1 with transient features shifted to lower energy, 1935 and 1875 cm-1. These transient bands correspond to a 1MLCT state that decays in <2 ps to a state that persists through the duration of the experiment, which is around 3 ns. This persistent state is assumed to be the T1 MLCT state. While the triplet state bands are primarily to lower energy than their parent ground state bleaches there may be some contribution from the Cr t2g orbital due to the weak peaks remaining at higher energy, 1980 and 1915(sh).

Figure 3.10. fsTRIR of compound 2 in THF, λex = 675 nm.

The spectra of 1 in the noncoordinating solvent, CH2Cl2, with excitation at 514 nm shows remarkably different excited state dynamics. See Figure 3.11. Again, the ground state bleaches are apparent at 1975 and 1905 cm-1, corresponding quite closely to the ‘A’ and

‘E’ bands seen in the steady state IR discussed previously. In addition to these bleaches, several broad transients appear to both higher and lower energy indicating an initial exited state quite different from that of 2. These peaks can roughly be assigned at, 1996,

1933, and 1870 cm-1, and correspond to a singlet state that lasts 18 ps and decays into a long lived triplet state with transient features apparent at higher energy, 1984 and 1919 cm-1. 60

Figure 3.11. fsTRIR of compound 1 in CH2Cl2, λex = 514 nm.

In comparing the spectra of 1 and 2 we can draw several conclusions. Perhaps the most apparent difference is the nature of the triplet states (red plot in both 3.10 and 3.11). The peaks that persists in 2 are shifted largely to lower energy indicating that the ν(CO) stretches have become more double bond-like due to the electron rich η6-benzoate allowing for more back bonding from the Cr t2g orbital to the CO π* orbitals . Compound

1 shows the opposite of this in its triplet state. The persistent peaks seen in 1 are to higher energy indicating some electron withdrawing effect on the η6-benzoate and thus the

Cr(CO)3 unit, removing Cr t2g-CO π* backbonding, causing the ν(CO) stretches to 61 become more triple bond-like. This electron withdrawing effect is explained well by the

3 assignment of a MoMoδδ* state which results in a hole on the Mo2 core which can pull density from the benzoate. See Figure 3.12 for a pictorial representation of the triplet excited states on the Cr(CO)3 unit.

Figure 3.12. A pictorial representation of the triplet excited states of 1 and 2 showing holes (red) and electron movement (blue.)

In addition to the difference in T1 states, the S1 excited states in 1 and 2 are significantly different. The S1 state in 2 simply shows two peaks shifted to lower energy with respect to the ground state, indicating a charge transfer from the W2δ orbital to the benzoate π* orbitals which consequently causes a red shift in the ν(CO) stretches. This finding is consistent with the lowest energy transition predicted by TD-DFT. The S1 state of 1, while at first glance more complex, can also be reconciled to the aforementioned calculations. The peaks that shift to lower energy with respect to the ground state are due to the orbital contributions of the Mo2δ orbital to the benzoate π* orbitals, much like in the case of 2. However, the peaks that appear at higher energy are caused by the mixing

62 of the Mo2δ and Cr t2g orbitals. This mixing allows for some contribution from a Cr t2g orbital to benzoate π* resulting in peaks at higher energy. A shift of this kind has been

6 100 seen before by George and coworkers while studying MeO2CC6H5-η -Cr(CO)3.

Figure 3.13. fsTRIR of compound 1 in THF, λex = 514 nm.

Initially, compound 1 was studied in the same solvent as 2, namely THF. In so doing the

TRIR spectra showed “ground state” bleaches that were shifted from those seen in the steady state FTIR by nearly 80 cm-1. See Figure 3.13. This disposition of the ground state bleaches is exceedingly unusual and implies that the compound being studied is not that which exists in the ground state or even in the noncoordinating solvent CH2Cl2. The most 63 likely explanation of this shift is an efficiently formed photoproduct that is produced within the time domain of the femtosecond pulse and is subsequently probed yielding a

TRIR of the photoproduct rather than 1. The production of photoproduct at the locus of the laser beam is aided by the fact that the stage of the liquid sample holder is not mechanically translated or the solution flowed through the cell during the course of the experiment. When the cell is moved manually by the synthetic chemist we can observe a spectra that is in essence the sum of the photoproduct, Figure 3.13, and the spectra of 1 in

CH2Cl2, Figure 3.11. See Figure 3.14.

Figure 3.14. fsTRIR of compound 1 in THF with manual stage translation, λex = 514 nm.

3.3 Conclusions

Metal carbonyls are attractive IR markers to study ultra fast charge transfer in M2 complexes. The addition of Cr(CO)3 causes a large stabilizing effect to the electronic structure which in turn shifts the 1MLCT further into the red. The lowest energy transition of these molecules is primarily M2δ to benzoate π*, however in the case of Mo2 there is a significant contribution from the Cr dπ orbital that is δ to the benzoate. This admixture could be causing the shift seen in the fs-TRIR data in THF, either through the loss of CO or some alternate mechanism.

In the cases where there is no photoproduct formed, such as tungsten or molybdenum in

CH2Cl2, the identity of the states was able to be determined. In the case of 1 the triplet state was found to be MoMoδδ* with a relatively long lifetime of 24 μs and an emission at 1100 nm with characteristic splitting. In compound 2 the lower energy W2δ to benzoate

π* transition leads to S1 and T1 states that are MLCT in character. These assignments were made by following the dynamics of the ν(CO) stretches.

3.4 Experimental

6 MeO2CC6H5- -Cr(CO)3 . Cr(CO)6 (6.8 g, 9.09 mmol) and methylbenzoate (2.1 g, 4.55 mmol) were added to a Schlenk flask along with 10 mL of THF and 100 mL of di-n-butyl ether. The colorless solution was refluxed for 12 hr, at which time the resulting orange solution was allowed to cool to room temperature. Solvent was removed in vacuo yielding a bright orange solid. The solid was recrystallized twice, first in dichloromethane

1 and finally in diethyl ether. H NMR (THF-d8, 400 MHz): 6.08 (d, 2H, JHH = 6.7 Hz ), 65

5.52 (t, 1H, JHH = 5.8 Hz), 5.25 (t, 2H, JHH = 6.2 Hz), 3.88 (s, 3H). UV-Vis-NIR (in THF

293K) 400, 312 nm.

6 6 HO2CC6H5- -Cr(CO)3. MeO2CC6H5- -Cr(CO)3 was dissolved in 30 mL of THF and thoroughly degassed 10% KOH solution in H2O. After 2 hr of stirring the THF was removed and the remaining aqueous solution was washed 2x100 mL with Et2O and acidified with 2 M HCl yielding an orange solid. The aqueous layer was washed multiple times with Et2O. The aqueous layer was removed and the resulting orange solution was

1 dried in vacuo yielding an orange solid. H NMR (THF-d8, 400 MHz): H 11.33 (s, 1H, vb). 6.16 (d, 2H, JHH = 6.7 Hz ), 5.71 (t, 1H, JHH = 6.0 Hz), 5.46 (t, 2H, JHH = 6.0 Hz).

6 6 Mo2(TiPB)2[O2CC6H5- -Cr(CO)3]2 (1) HO2CC6H5- -Cr(CO)3 (105 mg, 0.813 mmol) and Mo2(TiPB)4 (480 mg, 0.406 mmol) were added to a Schlenk flask and stirred in 20 mL of diethyl ether and 40 mL of THF. After 7 days a bright red precipitate and pale yellow solution formed. The precipitate was filtered and washed with diethyl ether (3 x

1 20 mL) and recrystallized from benzene. H NMR (THF-d8, 400 MHz): H 7.09 (s, 4H),

6.65 (d, 4H, JHH = 7.0 Hz), 6.20 (t, 2H, JHH = 6.5 Hz), 5.81 (t, 4H, JHH = 7.0 Hz), 2.92 (m,

6H), 1.23 (d, 12H, JHH = 7.1 Hz), 1.14 (d, 24H, JHH = 7.1 Hz). UV-Vis (in THF 293K)

470, 322 nm.

6 6 W2(TiPB)2[O2CC6H5- -Cr(CO)3]2 (2) HO2CC6H5- -Cr(CO)3 (105 mg, 0.813 mmol) and W2(TiPB)4 (550 mg, 0.406 mmol) were added to a Schlenk flask and stirred in 20 mL of diethyl ether and 40 mL of THF. After 7 days a dark blue precipitate and pale yellow solution formed. The precipitate was filtered and washed with diethyl ether (3 x 20 mL)

1 and recrystallized from benzene. H NMR (THF-d8, 400 MHz): H 7.08 (s, 4H), 6.39 (d, 66

4H, JHH = 7 Hz), 5.72 (t, 2H JHH = 5 Hz), 5.56 (t, 4H, JHH = 7 Hz), 3.02 (m, 2H), 2.90 (m,

4H), 1.24 (d, 12H), 1.19 (d, 24H). UV-Vis-NIR (in THF 293K) 651, 404, 321nm. (Note:

After several recrystallizations and washings 1 equivalent of free H-TiPB remained in the

NMR)

CHAPTER 4 : THE STUDY OF PMTReCl(CO)3 AND ITS EFFECT ON THE

PHOTOPHYSICS OF Mo2 PADDLEWHEELS

Adapted from a 2013 publication in The Journal of Physical Chemistry – A30

4.1 Introduction

Transition metal complexes that are pseudo-octahedral and contain an electronic configuration of d6 are pivotal in our understanding of inorganic photophysics. The

MLCT excited states seen in complexes Ru2+-polypyridyls and Ir3+-cyclometalated species (Figure 4.1) arise from an electronic promotion from the metal t2g orbital to a ligand π* orbital.105,106 Transition metals of this kind have received a great deal of attention for their ability to undergo facile electron transport107–109 for use in

DSSCs,60,69,110 sensors,111 and light emitting diodes.112 Second and third row compounds of this kind are notorious for having extremely short lived 1MLCT states as ISC is much more efficient due to increased spin orbit coupling.113–116

Figure 4.1. Examples of d6 metal complexes that show 1MLCT transitions.

The successful implementation of the organometallic moiety, Cr(CO)3, in Chapter 3 lead to a search for more viable metal carbonyl complexes that are tolerant of carboxylic acid functional groups. One such family of compounds are rhenium tricarbonyl chloride poly- pyridyl complexes. In the mid-1980s Jean-Marie Lehn and Thomas Meyer were the first to study this family of molecules as photo- and electrocatalysts for the reduction of CO2

117–119 to CO. The most frequently studied of these molecules was Re(bpy)(CO)3Cl where bpy = 2,2’ bipyridine. Recently the photophysics120–123 of this molecule as well as its role in catalysis124–126 has become more well understood. The key to photocatalytic properties of Re(bpy)CO3Cl is the Re t2g to bpy MLCT transition which absorbs from 250 – 450 nm.

The well studied photophysics of Re(bpy)CO3Cl as well as rhenium’s ability to tolerate carboxylic acids made this class of molecules an interesting ligand candidate. As a mono carboxylic acid of the Re(bpy)CO3Cl moiety is synthetically quite challenging a commercially available ligand was substituted for bpy, namely 2-(2-pyridyl)-4- methylthiazol carboxylic acid (PMT-H) which is seen below in Figure 4.2. This change 69 serves to slightly lower the LUMO of the lowest energy π* orbital but maintains the binding mode of bpy.

Figure 4.2. 2-(2-pyridyl)-4-methylthiazol carboxylic acid, PMT-H.

4.2 Results and discussion

4.2.1 Synthesis

The monoacid 2-(2-pyridyl)-4-methylthiazol carboxylic acid (PMT-H) is commercially available and is a reasonable analogue to the much more difficult to prepare carboxylic acid bipyridyl. The organometallic ligand Re(PMT-H)(CO)3Cl, HL, was prepared by refluxing a one to one ratio of PMT-H and Re(CO)5Cl in methanol for several hours. See

Scheme 4.1. As two equivalents of CO are librated the solution changes from a yellow slurry to a red solution. Upon cooling a red precipitate is formed which can be washed and recrystallized from hot methanol to yield air-stable x-ray quality crystals.

Scheme 4.1. Synthesis of HL

i The compound trans-Mo2(T PB)2(PMT)2, 1, was prepared from the exchange reaction

i involving two equivalents of PMT-H and Mo2(T PB)4 in toluene. See Scheme 4.2.

Compound 1 is a bright red solid that is soluble in THF and DMSO, slightly soluble in toluene and insoluble in hexanes.

Scheme 4.2. Synthesis of 1

i The organometallic compound trans-Mo2(T PB)2[PMTRe(CO)3Cl]2, 2, was prepared by

i reacting two equivalents of HL and one equivalent of Mo2(T PB)4 in a minimum of toluene. See Scheme 4.3. 2 is a dark blue color in THF, from which it is recrystallized. It should be noted that if large amounts of toluene are used for the synthesis of 2 scrambling can occur causing significant contamination with mono-, di-, and tri- substituted

71 complexes. This is likely due to the sparing solubility of 2 and its derivatives in toluene.

i To combat this problem a saturated solution of Mo2(T PB)4 should be added to HL.

Scheme 4.3. Synthesis of 2

Both 1 and 2 are highly air sensitive and were stored under inert atmosphere. They were characterized using 1H NMR, UV-Vis spectroscopy, MALDI-MS, and FT-IR spectroscopy.

To ensure that the commercially available PMT-H ligand is a reasonable analogue for the

i much more difficult to produce bpy-CO2H, small amounts of Mo2(T PB)2(O2C-bpy)2 (3) were made. 3 was characterized using 1H NMR, UV-Vis spectroscopy, MALDI-MS, and

FT-IR spectroscopy. The synthesis of 3 was similar to 1 and 2 and can be seen in Scheme

4.4.

Scheme 4.4. Synthesis of 3

4.2.2 Solid State Molecular Structure

i Single crystals of Mo2(T PB)2(O2C-bpy)2 were isolated by slow evaporation of THF. The crystals were isolated as bright red plates and handled under a pool of fluorinated oil. A crystal measuring 0.38 mm X 0.38 mm X 0.04 mm was placed on a glass fiber under an oxford cryostream at 200 K.

The structural refinement showed the bipyridyl ligands to be in a trans orientation and in

i conjugation with their respective CO2 groups. The supporting T PB groups were twisted out of conjugation by a torsion angle of 93o. Two THF moieties were coordinated to the z-axis of the Mo-Mo bond and are related by an inversion center. Furthermore, one additional THF molecule was found in the density map that was not associated with the main residue. Both this THF and an isopropyl group from the TiPB ligand were disordered in two locations. This disordered was handled by refining the two positions with similarity restraints and thermal restraints on the appropriate anisotropic U values.

The occupancy of the two locations was allowed to refine as a free variable summing to

1. The nitrogens on the bpy ligands were modeled in a trans configuration to one another based on their electron density and the fact that hydrogen atoms appeared in the density map around all atoms assigned as carbon prior to their being constrained to specific sites.

An ORTEP representation of 3 can be seen below in Figure 4.3.

Figure 4.3. ORTEP representation of 3 drawn at 50% probability. Disorder, solvent molecules and hydrogens excluded for clarity. Gray = Carbon, Blue = Nitrogen, Scarlet = Oxygen, Seafoam = Molybdenum.

Single crystals of RePMT(CO)3Cl were isolated by slow cooling of MeOH . The crystals were isolated as bright orange rods and handled under a pool of fluorinated oil. A crystal measuring 0.23 mm X 0.23 mm X 0.12 mm was placed on a glass fiber under an oxford cryostream at 150 K.

Structural refinement showed that the PMT ligand chelated one Re(CO)3Cl moiety in an

N-N fashion rather than a N-S fashion. Furthermore, the Cl was bonded in a fac manner rather than mer. The N-Re-N bite angle was found to be ~75o. There was one solvent methanol in the lattice that did not directly interact with the main residue. There were however some hydrogen bonding interactions between the solvent methanol and CO moieties in adjacent unit cells. An ORTEP representation of HL can be seen below in 74

Figure 4.4. Structural details and relevant crystallographic information can be found at the end of this chapter.

Figure 4.4. ORTEP representation of HL drawn at 50% probability. Solvent molecules and hydrogens excluded for clarity. Gray = Carbon, Blue = Nitrogen, Scarlet = Oxygen, Lime = Chlorine, Yellow = Sulfur, Orange = Rhenium.

4.2.3 UV-Visible Absorption Spectroscopy

A comparison of the electronic absorption specta of HL, 1 and 2 can be seen in Figure

4.5. In all three cases a peak can be seen at high energy near 325 nm which correlates to the π to π* transition of PMT. Compound 1 and 2 have broad, intense 1MLCT peaks at

510 nm and 603 nm respectively. These transitions arise from the Mo2δ to ligand π* charge transfer. The nearly 100 nm change in energy of this peak will be explained further in the computational section. In addition to this Mo2δ to ligand π* charge transfer there is also a Re dπ to CO π* transition which manifests as a shoulder next to the

75 aforementioned PMT ππ* in both HL and 2. Just red shifted from that transition is the

Re dπ to PMT π* charge transfer band which can be seen as a weak band at ~400 nm.

Figure 4.5. Electronic absorption spectra of HL (black) in MeOH, 1 (red) in THF, and 2 (blue) in THF at room temperature.

The UV-Vis of 1 and 3 were compared to ensure that PMT-H is a reasonable analogue to

HO2C-bpy. The plot of 1 and 3 in THF at room temperature can be seen below in Figure

4.6. The gross features of the two are nearly identical with an intense π to π* transition at higher energy and a broad 1MLCT transition at ~500 nm. While there is considerable difference in the energy of the π to π* transitions (2,150 cm-1) there is very little

1 -1 difference in the λmax of the MLCT transition (470 cm ). With this in mind PMT-H can be considered a reasonable substitute for bpy-CO2H and studies on PMT based model

i complexes could be extrapolated to polymeric [Mo2(T PB)2(O2C-bpy-CO2)]n systems. 76

Figure 4.6. Electronic absorption spectra of 1 (blue), and 3 (red) in THF at room temperature.

4.2.4 Luminescence Studies

The emission of the ligand, HL, can be seen in Figure 4.7. HL emits at 640 nm upon excitation by 390 nm light which is indicative of a T1 Re  PMT-H state, which has

127 been seen previously in Re(CO)3Cl(NN) chelates.

Figure 4.7. Emission (green, ex = 390 nm), excitation (red, em = 650 nm), and

absorption (blue) spectra of Re(PMT-H)(CO)3Cl (HL) in MeCN at room temperature.

Compound 2 shows signs of emission when excited at 640 nm where there is an initial rise in intensity that is cut off by the limited range of our UV-Visible detector. See Figure

4.8. Compound 2 does however show another emission band in the near-IR region of

1100 nm. See Figure 4.9. This band appears to have vibronic progressions spaced ~360 cm-1 apart which correlates to the ν(MoMo) caused by a triplet state that is primarily

3MoMoδδ* in nature.

Figure 4.8. Emission (green, ex = 640 nm), excitation (red, em = 780 nm), and i absorption (blue) spectra of Mo2(T PB)2[Re(PMT)(CO)3Cl]2 (2) in THF at room temperature.

Figure 4.9. Near-IR emission spectra of 2 in 2-MeTHF at 77K, ex = 658 nm. Average spacing between vibronic features of 359 cm-1, corresponds to Mo-Mo stretch.

4.2.5 Ground State Infrared

The ground state infrared of HL and 2 in THF can be seen below in Figure 4.10. The intense bands in the region of 2100 – 1900 cm-1 correspond to the ν(CO) stretches. It is

4+ interesting that ligation of the HL ligand to the Mo2 core causes no apparent change to the carbonyl stretching frequency. This is in stark contrast to what was seen in the

i previous chapter when HO2C-C6H5Cr(CO)3 was used to make trans-M2(T PB)2[O2C-

6 C6H5 - η - Cr(CO)3], where M2 = Mo2 or W2. This indicates that the electron density of

6 η benzoate is greatly affected by ligation to the M2 core and confers that effect to the metal carbonyl, where as there is no such affect in the N^N chelated Re(CO)3Cl.

The three stretches seen in the IR are appropriate for a M(CO)3 complex with no symmetry. The bands, A(1), A(2), and A(3) are descended from two C3 bands, namely, A and E, however the lack of symmetry causes a significant splitting of the E band. These three IR modes are well resolved and appear at 2024, 1921, and 1898 cm-1, which are

128 similar to Re(bpy)(CO)3Cl.

HL also contains a C=O stretch from its carboxylic acid moiety at 1728 cm-1 which disappears after complexation to the Mo2 core. This, along with the other characterization methods used, is further evidence of the identity of 2. The lower energy stretches < 1600 cm-1 are likely due to ring stretches within the PMT ligand.

Figure 4.10. Ground state infrared spectra of HL (black) and 2 (blue) illustrating the

splitting of the ‘A’ and pseudo ‘E’ bands of the Re(CO)3Cl moiety (inset).

4.2.6 Electronic Structure Calculations

In order to better understand the photophysical studies of HL, 1, and 2, DFT and TD-

DFT calculations were undertaken. Similarly to Chapter 3, to save on computational time, 1 and 2 were represented by model complexes 1’ and 2’ which have TiPB substituted for formate. While compounds 1 and 2 were not structurally characterized in this work, it is reasonable to expect the trans arrangement of ligands around the Mo2 core that has been seen on numerous occasions in bis-bis tetracarboxylates of this form.18,129,130 The frontier molecular orbitals for HL can be seen below in Figure 4.11.

The HOMO is primarily Re t2g dπ in character. This orbital is stabilized by the

81 backbonding of the Re to the carbonyls and shows some mixing from a Cl p orbital. The

LUMO is dominated by PMT-H π* orbitals as are the subsequent LUMO+1 and +2 orbitals. It is important to note that the metal eg* orbitals are significantly higher in energy than these ligand π* orbitals. The lowest energy optical transition for HL is from the HOMO  LUMO and thus an MLCT.

Figure 4.11. GaussView131 representations of the HOMO and LUMO of HL.

Model compound 1’ showed a HOMO level that is predominately Mo2δ in nature with some mixing of the PMT ligand. The LUMO is an in-phase combination of the PMT π* that does not have the appropriate symmetry to interact with the δ bond. The LUMO+1, however, has an out-of-phase π* symmetry which is capable of interacting with the Mo2δ orbital. The calculated energy level of the HOMO is -5.09 eV and there is a HOMO –

LUMO gap of 2.76 eV.

The orbital energy diagram of 1’ can be seen in Figure 4.12 where it is compared to its organometallic counterpart, 2’. The gross features of the two are indeed similar, however the addition of a ReCl(CO)3 moiety causes significant changes to the energy.

The HOMO is stabilized significantly from that seen in 1’ by ~0.8 eV, down to -5.86 eV and is now mostly Re dπ based rather than Mo2δ based. This trend is also seen in

HOMO-1, -2 and -3 which form a tight band from the HOMO at -5.86 to the HOMO-4 at

-5.97 eV, where the Mo2δ orbital is found. The ordering of the LUMO levels remains the same from 1’ to 2’ however, like the HOMO levels, they are greatly reduced in energy.

The stabilization of the LUMO orbitals along with the addition of the Re dπ based

HOMO’s leads to a particularly small HOMO – LUMO gap of 2.28 eV.

TD-DFT predicts the most intense low energy transition for 1’ to be HOMO 

LUMO which is an MLCT from the Mo2δ orbital to the in-phase PMT π* orbital. This is similarly predicted for 2’ where the lowest energy transition is primarily from HOMO-4

 LUMO, however there is some involvement of a Re dπ orbital. Gaussview plots of 2’ can be seen in Figure 4.13.

Figure 4.12. Frontier molecular orbital energy level diagram of compounds 1’ (red) and 2’ (blue).

Figure 4.13. Select GaussView131 plots of model compound 2’ drawn at isovalue 0.03.

In an attempt to better understand the TRIR data presented herein the carbonyl stretching frequencies of 2’ are compared to those of the 2’- anion and the triplet state calculations of 2’. The results of this analysis will be discussed further in the TRIR discussion.

4.2.7 EPR Studies

With the discovery that the HOMO level of 2’ is Re based rather than Mo based it was prudent to investigate the nature of the oxidized species. Most Mo2 tetracaboxylates contain a Mo2δ based HOMO and when oxidized show a loss of an electron from the

4+ 5+ + - Mo2 core to form Mo2 . The oxidized species [2] PF6 was made by reacting 2 with ~1 equiv of AgPF6 in a THF solution in the glove box. EPR spectroscopy was then conducted on the oxidized product which yielded the spectra seen in Figure 4.14.

Interestingly the resulting spectra does not show an oxidized Re2+ ligand, but rather

5+ shows the characteristic splitting of a Mo2 core. The central resonance is located at g =

1.930 while the satellite peaks arise from the two magnetic nuclear states of molybdenum, where I = 0, is 74.5% abundant (red line) and I = 5/2, is 25.5% abundant

t + (blue lines). The Ao was found to be 26 G and is comparable to the Mo2(O2CBu )4 cation studied previously.132 There are two explanations for the selective chemical ionization of

Mo over Re: 1) the energy levels of the Re based HOMO and the Mo2 based HOMO-4 are relatively similar and could lead to preferential ionization or even electron transfer from the Mo2 core to the Re ligand within the time domain of the experiment and 2) the

Re dπ orbitals are coordinately saturated by the PMT ligand, Cl and CO while the Mo2 core is only weakly solvated along the MM axis. This could cause the Mo2 core to be the kinetically favored site of oxidation over the more highly encumbered Re center.

+ - Figure 4.14. EPR spectrum of 2 PF6 in THF at room temperature.

4.2.8 Ultra-fast Spectroscopy

To investigate the photophysical properties of HL, 1, and 2 a combination of fs- and ns- ultra fast techniques were employed including fs-TA, ns-TA and TRIR.

The excited state of 1 and 2 were studied using fs-TA. The molecules were excited into their lowest energy MLCT. Compound 2 was excited using 675 nm light and showed a broad transient peak centered around 495 nm with a slight shoulder at 440 nm that decayed with a lifetime of 12 ps. After ~25 ps a slight feature could still be seen at 440 nm which lasts throughout the duration of the experiment. This remaining feature is due to the absorption of the 3MoMoδδ* state. In addition to these transient features there is an apparent bleach from 570 to the low energy edge of the experiment that correlates to the decay of the S1 state. This spectrum can be seen in Figure 4.15. 87

The fs-TA of 1 is similar to its organometallic counterpart and is also shown in Figure

4.15. The S1 lifetime of 1 is similar to that of 2 with a lifetime of 10.8 ps. 1 also shows a transient feature at 500 nm and a bleach at 520 nm. The bleach persists through the duration of the experiment which is indicative of a long lived 3δδ* state. The similarity of the two transient species in 1 and 2 may indicate the nature of the 1MLCT state involving a delocalized state that is spread over both PMT ligands.

Figure 4.15. (a) fs-TA spectra of 2, ex = 675 nm, in THF/DMSO at room temperature (b)

fs-TA spectra of 1, ex = 568 nm, in THF at room temperature.

While the ns-TA is unable to identify the nature of the T1 state, it is capable of providing a lifetime of the persistent state seen at the end of the fs-TA experiment. Compound 1 when excited with 355 nm light gives a transient at ~400 nm and a bleach at ~515 nm which decay with a lifetime of 74 μs. This spectrum and its kinetic trace can be seen below in Figure 4.16.

Figure 4.16. (a) ns-TA spectra of 1, ex = 355 nm, in THF at room temperature; (b)

kinetic trace at 520 nm gives τ T1 = 73.6 ± 2.8 s.

Compound 2 when excited with 355 nm light gives a transient at ~450 nm and a bleach at

~565 nm which decay with a lifetime of 21 μs. This spectrum and its kinetic traces can be seen below in Figure 4.17.

i Figure 4.17. ns-TA spectra of Mo2(T PB)2[RePMT(CO)3Cl]2 , ex = 355 nm, in THF at room temperature (top). Kinetic trace of transient at 430 nm (left) and 570 nm (right) produced a lifetime () of 21.3 s.

As discussed in the introduction, there have been numerous TRIR studies on complexes of the form Re(N^N)(CO)3Cl, however, the PMT-H ligand has not be previously studied.

In order to compare these findings to the larger body of work regarding rhenium tricarbonyl halide complexes, a detailed TRIR of the ligand HL was necessary.

Following excitation at 345 nm, HL showed two distinct transients derived from two rhenium transitions, namely, Re dπ to CO π* and Re dπ to PMT-H π*. This causes a mixture of the two species and the spectra we see in Figure 4.18. After an initial intersystem crossing event taking less than <100 fs the triplet state leads to these two sets of CO stretches. After ~5ps the 3Re  CO state interconverts to the lower energy 3Re 

PMT-H state which is indicated by the disappearance of the lower energy CO stretches at

1870 and 1846 cm-1. The vibrations that remain decay slightly but ultimately last for the duration of the experiment (> 3 ns).

τ1 = 11.2 ± 2.6 ps τ2 > 1 ns -5.8 ps 0.23 ps 0.47 ps 0.62 ps 1.62 ps 5.44 ps 20.3 ps 61.2 ps 220 ps 1140 ps 2830 ps

Figure 4.18. Time Resolved Infrared Spectroscopy of HL in THF at room temperature.

The broad features to higher and lower energy that are prominent in HL stand in stark contrast to the TRIR of 2. See Figure 4.19. Once the ligand is coordinated to the Mo2 core the carbonyl region shows sharp ground state bleaches and transients which are shifted by

~17 cm-1 to lower energy. These excited state features decay with a lifetime of 11 ps. The shift of these bands to low energy is due to the electron that is injected from the Mo2δ orbital to the PMT moiety during the MLCT transition. This extra electron density causes the population of CO π* orbitals and thus a shift to lower energy. It is important to note that there are no transients seen to higher energy as was seen in HL which indicates there is no electron density being lost from the Re metal centers during the initial MLCT event.

i 6 This is in contrast to the Mo2(T PB)2[O2C-C6H5-η -Cr(CO)3]2, discussed in Chapter 3, which does show significant contributions from Cr during excitation.

Figure 4.19. Time Resolved Infrared Spectroscopy of 2 in THF/DMSO at room temperature upon excitation at 675 nm.

To better understand the charge delocalization of this singlet excited state it is perhaps prudent to revisit the aforementioned anion calculations. When 2’ is calculated as an anion the extra electron is spread evenly across the molecule, which emulates a fully delocalized singlet excited state that causes a red shift of the ν(CO) frequencies by ~18 cm-1. Thus we could expect a shift of ~18 cm-1 in a fully delocalized type III excited state, and a much larger shift if the electron is isolated on only one ligand.

Experimentally, we can see that the singlet state of 2 contains CO stretches that are shifted ~17 cm-1 to lower energy than the ground state which matches the delocalized 92 calculations quite well. From these results we can conclude that the S1 state of 2 is a type

III or delocalized excited state.133

3 After the decay of the S1 state of 2 to its MoMoδδ* state, weak peaks in the carbonyl region persist through the duration of the experiment. These peaks are higher in energy than the ground state bleach, indicating an electron withdrawing effect on the PMT ligand which is consistent with a hole located on the Mo2 core. This shift to higher energy is predicted by triplet state calculations on the model compound 2’. The experimental and calculated shifts of 2, along with their assigned states can be seen in Table 4.1 and 4.2 respectively.

1 3 S0 ν(CO) / MLCT ν(CO) MoMo* ν(CO) cm-1 (Δν (CO)) / cm-1 (Δν (CO)) / cm-1

A(1) 2024 2009 (-15) 2027 (+3)

A(2) 1921 1902 (-19) 1923 (+2)

A(3) 1898 1890 (-18) 1902 (+4)

Table 4.1. Experimental shifts of the 1MLCT and 3MoMo* ν(CO) stretches of 2.

S0 ν(CO) / Anion ν(CO) T1 ν(CO) cm-1 (Δν(CO)) / cm-1 (Δν (CO)) / cm-1

A(1) 2013.9 1996.2 (-17.7) 2015.1 (+1.2)

A(2) 1946 1926.2 (-19.8) 1948 (+2)

A(3) 1921.7 1903.5 (-18.2) 1922.3 (+0.6)

Table 4.2. Calculated shifts of the anion and triplet ν(CO) stretches of 2’.

The most striking feature of the plot in Figure 4.19 is perhaps not in the carbonyl region of 2, but rather in the lower energy region containing CO2 and PMT ring vibrations.

These vibrations are interesting because of their intensity, both relative to the carbonyl stretches (which are notoriously intense) and relative to other compounds examined in the

Chisholm laboratory.18,134 These intense bands are not seen as prominently in the spectra for HL and 1, and while this change in intensity is not fully understood at this time, it clearly indicates that the inclusion of ReCl(CO)3 produces new properties that are not seen in either the organometallic ligand or the simple bis-bis individually.

While there are no carbonyl stretches to follow in compound 1 there is still the CO2 stretch of the Mo2 tetracarboxylate core to consider. These two modes are found at 1450

-1 and 1545 cm which decay to the stretch seen at 1540 which is indicative of the

3MoMoδδ* state. These spectra can be seen in Figure 4.20.

Figure 4.20. Time Resolved Infrared Spectroscopy of 1 in THF at room temperature upon excitation at 550 nm.

4.3 Conclusions

i The organometallic complex Mo2(T PB)2[PMTRe(CO)3Cl]2, 2, was synthesized and its photophysical properties were compared to the ligand H-PMTRe(CO)3Cl, HL, and the

i Re free complex Mo2(T PB)2(PMT)2, 1. HL was found to be a reasonable analog for the

3 well studied Re(bpy)(CO)3Cl compound. HL was shown to populate two MLCT states following excitation with the higher energy state representing Re  CO π* which undergoes internal conversion to the lower energy Re  PMT-H π* state within 5 ps.

The excited state dynamics of Compound 1 are similar to other Mo2 complexes previously studied, showing an initial population of a PMT based 1MLCT state followed 95 by conversion to the 3MoMoδδ* state. The organometallic compound 2 showed enhanced coverage of the visible spectrum along with stabilization of the Mo2δ based HOMO and the PMT π* based LUMO to cause a remarkable red shift of the 1MLCT band. Upon excitation into the S1 state the electron serves to enhance the Re dπ to CO π* backbonding causing a decrease in the CO stretching frequency. This 1MLCT state interconverts to the triplet MoMoδδ* state causing the CO stretching frequency to shift to slightly higher energy due to the hole residing on the Mo2 unit. The interesting photophysical properties of this class of molecules make them promising subjects for future materials.

4.4 Experimental

Synthesis of Re(PMT-H)(CO)3Cl (HL). PMT-H (0.058g, 0.28 mmol) and Re(CO)5Cl

(0.1g, 0.28 mmol) were refluxed in MeOH under argon for 2 hours. The solution went from colorless to bright red. The solvent was removed in vacuo to yield 147 mg (51%) of bright orange solid. X-Ray quality crystals were obtained slow cooling in MeOH. NMR

(DMSO- d6): H (400 MHz) 9.05 (d, 1H, JHH = 5Hz ), 8.62 (d, 1H, JHH = 8Hz), 8.34 (t,

1H, JHH = 8Hz), 7.81 (t, 1H, JHH = 6Hz), 2.92 (s, 3H). UV-Vis: (in MeOH at 293K) 327 nm, 341 nm, 385 nm (sh). FT-IR (KBr, cm-1) 2027, 1915, 1896, 1723.

i i Synthesis of Mo2(T PB)2(PMT)2 (1). PMT-H (0.075g, 0.34 mmol) and Mo2(T PB)4

(0.2g, 0.17 mmol) were dissolved in toluene and allowed to stir for 3 days yielding a red solution. The solvent was removed in vacuo and the resulting red solid was washed 3 times with 20 ml of hexanes and dried. NMR (THF- d8): H (400 MHz) 8.61 (d, 2H, JHH 96

= 4Hz ), 8.28 (d, 2H, JHH = 8Hz), 7.90 (t, 2H, JHH = 7Hz), 7.41 (t, 2H, JHH = 6Hz), 7.04

(s, 4H), 3.17 (m, 4H) 2.99 (s, 6H), 2.89 (m, 2H), 1.25 (d, 12H, JHH = 6Hz), 1.16 (d, 24H,

JHH = 8Hz). UV-Vis: (in THF at 293K) 512 nm, 313 nm; (in Toluene at 293K) 490 nm,

313 nm. MALDI-TOF: Calculated: 1128.06. Found: 1124.3 (M+), 1147.8 (M+ + Na+).

i Synthesis of Mo2(T PB)2[Re(PMT)(CO)3Cl]2 (2). Re(PMT-H)(CO)3Cl (0.095g, 0.18

i mmol) and Mo2(T PB)4 (0.11g, 0.09 mmol) were dissolved in toluene and allowed to stir for 3 days yielding green-blue solution and blue precipitate. The solvent was removed in vacuo and the resulting blue solid was washed 6 times with 20 ml of hexanes and dried.

The solid was then recrystallized from hot THF yielding a microcrystalline blue compound. NMR (DMSO- d6): H (400 MHz) 9.13 (d, 2H, JHH = 5Hz ), 8.77 (d, 2H, JHH

= 8Hz), 7.86 (t, 2H, JHH = 7Hz), 7.10 (s, 4H), 3.22 (s, 6H), 2.99 (m, 4H), 2.91 (m, 2H),

1.22 (d, 12H, JHH = 7Hz), 1.12 (d, 24H, JHH = 7Hz). UV-Vis: (in THF at 293K) 607 nm,

383 nm, 324 nm. FT-IR [KBr, cm-1, (CO)]: 2022 (s), 1921 (s), 1897 (s).

i Synthesis of Mo2(T PB)2(O2C-bpy)2 (3)

135 i HO2C-bpy (0.095g, 0.18 mmol) and Mo2(T PB)4 (0.11g, 0.09 mmol) were dissolved in toluene and allowed to stir for 4 days yielding a dark red precipitate with a pale yellow solution. The solid was filtered and washed 3 times with 20 ml of toluene and 2 times with 20 ml of hexanes and dried. The solid was then recrystallized through the slow evaporation of hexanes into THF. NMR (THF- d8): H (400 MHz) 9.59 (s, 2H), 8.78 –

8.71(m, 6H), 8.65 (d, 2H), 7.91 (td, 2H), 7.39 (td, 2H), 3.08 (m, 4H), 2.87 (m, 2H), 1.22

(d, 12H), 1.07 (d, 24H). UV-Vis: (in THF at 293K) 498, 337, 292 nm. MALDI-TOF:

Calculated: 1088 m/z, Found: 1088 m/z.

Compound HL 3 Chemical Formula C14H12ClN2O6ReS C70H92Mo2N4O12 Formula Weight 557.97 1373.36 Temperature (K) 150(2) 200(2) Space Group Monoclinic, P21/c Triclinic, P-1 a (Å) 11.5966(1) 10.7291(2) b (Å) 8.9428(1) 13.3780(2) c (Å) 17.4184(3) 14.2222(2)  (o) 67.159(1) β (o) 97.950(2) 68.494(1)  (o) 89.671(1) V (Å3) 1789.03(3) 1727.98(5) Z 4 1 3 Dcalcd (Mg/m ) 2.072 1.320 Crystal Size (mm) 0.23 X 0.12 X 0.12 0.38 X 0.38 X 0.04 Theta range for data collection 1.77 to 27.48o 1.82 to 27.45o ,(Mo, K) (mm-1) 7.090 0.424 Reflections collected 36971 49413 Unique reflections 4099 [R(int)= 0.0250] 7883 [R(int)= 0.0206] Completeness to theta (27.48o) 99.9% (27.45o) 99.7% Data/restraints/parameters 4099 / 0 / 229 7883 / 129 / 462 a R1 (%) (all data) 2.92 (4.65) 3.51 (4.77) wR2b(%)(all data) 6.95 (9.93) 8.60 (9.23) Goodness-of-fit on F2 1.166 1.038 Largest diff. peak and hole (e Å-3) 2.213 and -1.171 0.633 and -0.501

a R1 =  | |Fo|-|Fc| | /  |Fo| b 2 2 2 2 2 1/2 wR2 = {  [w( Fo -Fc ) ] /  [ w(Fo ) ] }

Table 4.3. Select crystallographic information from structure HL and 3.

CHAPTER 5 : A COMPUTATIONAL STUDY OF M2-Pt ACETYLIDE HYBRID

POLYMERS

5.1 Introduction

Functional materials derived from metal containing polymers have been an area of considerable research over the last few decades.34 Chapters 3 and 4 have primarily focused on small molecule model complexes designed to represent metal polymers. The merits of studying discrete model complexes prior to studying complex polymers have been discussed previously. However, in order to understand the electronic properties of the final material it is desirable to conduct detailed computational studies of monomers and oligomers using density functional theory (DFT) and time dependent density functional theory (TD-DFT).49 These studies can elucidate the nature of the frontier molecular orbitals that contribute to charge transfer as well as the material’s optical properties.

A metal polymer consisting of M2 repeating units would contain many of the properties desired in an efficient photon harvesting material, such as: 1) the ability to absorb a large

99 amount of light, with ε ranging from 20,000 to >80,000 mol-1cm-1 depending on the metal and attendant ligand, 2) a tunable metal-to-ligand charge transfer band from 350 nm to

<900 nm, and 3) long lived (3-20 ps) singlet states that are 1MLCT based.29 Monomers of

M2 tetra-carboxylates however tend to form crystalline domains when spin coated or drop-cast, which impedes device performance due to low donor-acceptor contact. To combat this, soluble M2 containing polymers are being studied. These polymers are thought to maintain the attractive photophysical properties of the monomer but will likely be less crystalline when processed into a thin film.

Previous attempts to synthesize MM containing polymers linked by a dicarboxylate as

49 simple as oxylate (O2C-CO2) have led to cyclization rather than polymerization. In order to insure a linear material Chisholm and co-workers have recently reported a

i i discreet monomer, M2(T PB)2(O2C-Th-CCH)2, (where M2 = Mo2 or W2, T PB = 2,4,6- triisopropylbenzoate, and Th = thiophene) which can be functionalized by cross-coupling organohalides onto the terminal acetylide, or by the addition of another metallic species

134 like AuClPPh3 , the results of which can be seen below in Figure 5.1.

100

Figure 5.1. Synthesis and functionalization of a quadruply bonded molybdenum tetracarboxylate with organic and organometallic substituents.134

This report alludes to the eventual use of other metals, like platinum, as a linking group, as platinum acetylides are already well studied metal-containing polymeric materials.38,39

By shifting the point of polymerization from the carboxylic acid, which can cause scrambling and cyclization, to the acetylene, which has been well known to form polymers with platinum, a well defined M2-Pt acetylide polymer could be made. A general example of the proposed synthesis of one of these polymers can be seen below in

Scheme 5.1.

101

Scheme 5.1. Proposed synthesis of M2Pt acetylide hybrid polymers where M = Mo or W.

The aim of this chapter will be to determine the electronic and spectroscopic properties of

i the simplest M2 carboxylate acetylene unit, M2(T PB)2(O2CCCH)2 and investigate the effects of coupling such a moiety to Pt(PBu3)2 linkers. The results of this study will help guide synthetic chemists in the future as to the electronic structure and absorption profile of M2-Pt acetylide polymers. Eight oligomers will be discussed using DFT and TD-DFT methods, with chains containing 1-4 bridging Pt(PH3) units and 2-5 M2 units.

102

5.2 Approximations and Methods

i n Due to the large size of polymers containing T PB and P Bu3 ancilary ligands it is necessary to make several approximations to limit the computational costs of calculating their electronic structures. These approximations aim to ensure that the electronic and photophysical properties of the final molecules are accurate while using a reasonable amount of computational resources.

The first approximation used is one previously seen many times in this thesis, namely, the replacement of TiPB ligands with formate ligands. As discussed previously, this approximation has limited influence on the electronic properties of the final product. The next approximation concerns the phosphine ligands, which are typically ethyl, butyl or phenyl derivatives. To simplify the calculation these have been changed to PH3 ligands under the assumption that the aliphatic butyl orbitals do not largely influence the electronics of the phosphines. While it is true that the carbons themselves do not greatly change the electronics of the phosphines directly, this assumption will change the

o o phosphines cone angle from ~118 in –CH2– to 87 in –H which may influence the electronics of the platinum core slightly. With this being said this should be a nominal change and calculations of large models were unstable when calculated with any phosphine larger than PH3.

The computational level used was B3LYP77 as it has shown to perform well on molybdenum containing species in the past and gives reasonable values for that of tungsten.78 Tungsten and platinum are third row transition metals whose relativistic effects can make calculations difficult, especially those involving TD-DFT. It is not

103 unusual for simulated UV-Vis spectra containing tungsten to be estimated to higher energy by more than 100 nm.49 In general, however, DFT and TD-DFT give very accurate results for molybdenum containing species and are able to simulate the gross features of complexes containing tungsten.

Due to the aforementioned relativistic effects it was necessary to employ two different basis sets. 6-31G* was utilized for all light atoms (C, O, P, H)79 where the SDD basis set and pseudo potential was used for all heavy atoms (Mo, W, Pt).78

All calculations were run using Gaussian 0975 and all orbital diagrams were imaged using

Gaussview 5.0.9

5.3 Results and Discussion

The first question that must be answered is that of the orientation of the attendant phosphines with respect to the plane of conjugation. In most cases of platinum acetylides the P-Pt-P axis is perpendicular to that of the plane of conjugation,43 but given the conditions set forth in this investigation it is not unreasonable to expect the P-Pt-P bond to be parallel to that of the plane of conjugation. One reason for this difference which is not explicitly shown is born out of our approximations. If two bulky TiPB groups were brought into close proximity to one another separated by only two acetylene bridges and one Pt metal center there would be a great deal of steric encumbrance. This steric effect

n would prevent the P Bu3 moieties from occupying the space they usually do and force them to be parallel to the plane of conjugation.

104

Before moving to longer oligomers the simplest “dimer of dimers”,

[Mo2(O2CH)3]O2CCC-Pt(PH3)2-CCCO2[Mo2(O2CH)3] (Mo22Pt), was analyzed. After a geometry optimization and vibrational analysis of both conformers it was found that even without the aforementioned steric encumbrance, which would almost certainly be a factor in a real material, the parallel geometry was slightly favored. The lowest energy geometries of both the perpendicular arrangement and the parallel arrangement can be seen below in Figure 5.2. This slight energy difference is likely due to enhanced

2 conjugation that is attained by the platinum metal center when its dz orbitals run

2 perpendicular to those of the M2 dz orbitals.

Parallel -74,656.20 eV Perpendicular -74,656.16 eV

Figure 5.2. Optimized geometric configurations of Mo22Pt.

As the parallel configuration was found to be slightly lower in energy than the perpendicular configuration it was the motif used for the duration of the calculations.

To determine the effect length has on photophysical properties and electronic structure, four different lengths were investigated with an increasing number of bridging Pt(PH3)2

105 units and M2(O2CH)2 units. The optimized geometry of these oligomers, M22Pt, M23Pt2,

M24Pt3, and M25Pt4 (where M2 = Mo2 or W2) can be seen below in Table 5.1.

106

Molecule M = Mo M = W M22Pt

M23Pt2

M24Pt3

M25Pt4

Table 5.1. GaussView plots of the lowest energy structures of M22Pt – M25Pt4

5.3.1 Electronic Structure

In order to understand the electronic structure of multiple repeating units, it is necessary to understand the bonding in the simplest unit M22Pt. From a detailed analysis of M22Pt we can discover the principle orbitals in bonding and better track them when calculating a

107 longer chain. A molecular orbital (MO) diagram along with GaussView plots of the

MO’s from Mo22Pt and W22Pt can be seen below in Figure 5.3.

Figure 5.3. MO diagram comparing the frontier molecular orbitals of Mo22Pt and W22Pt along with GaussView plots of Mo22Pt.

The HOMO and HOMO-1 level consists of in and out of phase combinations of M2δ orbitals which are slightly more stabilized in the case of the molybdenum containing

12 species. This is a common occurrence in M2 containing dimers-of-dimers. Even further to lower energy are the various combinations of M2π, M2σ, and Lπ orbitals. The LUMO

108 of both compounds consists of a ligand π* orbitals with major contributions from the acetylide and the phosphines and very slight contribution from the platinum. The

LUMO+1 and +2 in the case of molybdenum are the in and out of phase combinations of

Mo2δ* orbitals. These orbitals can be found at the LUMO+3 and +4 level in the case of

W2 which are raised significantly in energy which has been noted previously.

The general trends seen in the comparison between Mo2 and W2 have been seen on numerous occasions previously, both in this document and others and are not particularly noteworthy. What is perhaps more interesting is the comparison between oligomer lengths. A graphical illustration of the molecular orbitals comparing Mo22Pt, Mo23Pt2,

Mo24Pt3, and Mo25Pt4 can be seen below in Figure 5.4.

109

Figure 5.4. Molecular orbital diagram comparing Mo22Pt, Mo23Pt2, Mo24Pt3, and

Mo25Pt4.

The change in the HOMO-LUMO gap is immediately obvious as it decreases significantly, more than 0.2 eV, as units are added from Mo22Pt to Mo23Pt2. This is due to the increased conjugation that is inherent in adding multiple Mo2 units. However, this trend is not as pronounced as we continue from Mo24Pt3 to Mo25Pt4. The HOMO-

LUMO gap stays relatively the same as we add more repeating units and the relative positions of the HOMO and LUMO do not change significantly. This indicates the

110

HOMO-LUMO gap of the model compound consisting of five Mo2 units and four Pt units is characteristic of a much larger polymer.

Another interesting gross feature is the formation of manifolds or bands. Due to the various combinations of orbitals that arise with the increased number of repeating units there are many similar orbitals that occupy similar energies. This forms a band that gets more and more populated as repeat units are added. One rather scarcely populated manifold is the “band” that forms from the Mo2δ combinations. This “band” forms near the HOMO level and is relatively diffuse compared to the bands found at lower energy.

This band formation has been seen in a recent publication by Chisholm and coworkers49, which investigated repeating units of M2 paddlewheels bridged by simple oxalate ligands.

Further below the Mo2δ manifold is a band that consists of Mo2π, Mo2σ and Lπ combinations. These orbitals form a true band between -6.50 and -7.0 eV. The number of orbitals that make up this band increases significantly as more units are added (Mo22Pt =

5, Mo23Pt2 = 11, Mo24Pt3 = 14, and Mo25Pt4 = 21). The unoccupied orbitals do not have domains that are as well defined as in the occupied orbitals, but it is possible to see how the Mo2δ* and Lπ* orbitals may form these domains as well if the polymers were extended to ∞.

The visualization of these bands along with the elucidation of the orbital character from which they are composed is important in understanding their potential properties as semiconductors. Furthermore it should be noted, this investigation is based on the simplest platinum acetylde bridging group. It is likely that other organics like thiophenes

111 or polythiophenes will be used which will allow for the tuning of these bands to fit the desired electronic properties.

Figure 5.5. Molecular orbital diagram comparing W22Pt, W23Pt2, W24Pt3, and

W25Pt4.

A molecular energy diagram featuring W22Pt - W25Pt4 can be seen in Figure 5.5. The

W2 complexes show trends similar to Mo2 in that the HOMO-LUMO gap decreases from

2.61 eV in W22Pt to 2.31 eV in W25Pt4 with very little change in the HOMO/LUMO energy levels between W24Pt3 and W25Pt4. Again, it can be seen that the higher energy domains forming from -4.58 – -4.31 eV are made up of various W2δ combinations. 112

Lower in energy we see the formation of two distinct domains, one from -6.08 to -5.87 and another from -6.72 to -6.52. The higher energy domain is formed from W2π orbital combinations while the lower energy domain is made up of Lπ and W2σ orbitals. In the case of molybdenum the lower energy Mo2π orbitals were at the same level as the Lπ orbitals forming only one large band, due to the inherently higher energy of W2π orbitals we see a separation of this band.

5.3.2 Optical Properties

The optical properties of these molecules were also studied to determine their coverage of the solar spectrum and their tunability. As such, TD-DFT calculations were performed to simulate each model’s UV-Visible spectra by calculating their allowed optical transitions.

There are two main transitions found in these systems. To higher energy we see a peak that represents the ligand ππ* transition and with an admixture of Pt d to Lπ* transitions.

The lower energy transition is the result of a Metal-to-Ligand charge-transfer (MLCT).

Below in Figure 5.6 the dominate low energy optical transition can be seen which involves the HOMO to LUMO transition and the removal of an electron from the M2δ orbital to a Lπ* orbital that has ethynyl and phosphine character.

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Figure 5.6. HOMO (left) and LUMO (right) of Mo22Pt, which is the dominate low energy transition.

This HOMO to LUMO MLCT is the dominate transition for each molecule studied and the intensity is seen to increase as more repeat units are added. The increase in intensity is likely due to the fact that different Mo2δ  Lπ* combinations are allowed transitions and contribute to the oscillator strength. For example, Mo24Pt3 contains an absorption made up of three orbital transitions, HOMO – LUMO, HOMO-1 – LUMO+1, and

HOMO – LUMO+4. The orbitals that make up this transition can be seen below in Figure

5.7.

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HOMO LUMO

HOMO-1 LUMO+1

HOMO LUMO+4

Figure 5.7. Various Mo2δ – Lπ* combinations that contribute to the low energy transition in Mo24Pt3.

This low energy MLCT band also red shifts as more repeat units are added. This observation is consistent with the electronic structure calculations discussed previously and the decrease in the HOMO-LUMO gap as the oligomers were made longer. This red shifting is likely due to the increased conjugation along the chain as more monomeric units are added. The simulated UV-Visible spectra of the four dimolybdenum oligomers

115 is compared below in Figure 5.8 and the UV-Visible spectra for the analogous ditungsten oligomers can be seen in Figure 5.9

Figure 5.8. Simulated gas phase UV-Vis spectra of dimolybdenum containing oligomers.

Figure 5.9. Simulated gas phase UV-Vis spectra of ditungsten containing oligomers.

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5.4 Conclusions

A series of dimolybdenum and ditungsten oligomers were studied which have platinum acetylide bridging groups supported by PH3 ligands. The electronic structure calculation showed a decrease of the HOMO-LUMO gap as more repeat units were added which was confirmed in the TD-DFT investigation of the simulated UV-Visible spectra.

Furthermore, it was found that even at a relatively short chain length of five M2 units, prominent domains or bands were formed that consisted of many different combinations of M2 and Pt d orbitals. These findings support that a hybrid M2/Pt polymer would have interesting electronic and photophysical properties which could have a significant impact on the field of photovoltaics.

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CHAPTER 6 : THE EFFECT OF PYRIDYL N-OXIDE LIGANDS ON Mo2

PADDLEWHEELS AND THEIR POTENTIAL APPLICATION AS ANCHORING

GROUPS

6.1 Introduction

M2 carboxylates have been used as test beds for mixed-valence compounds in several instances.136–138 In the simplest form a mixed valence compound contains two redox active groups separated by a bridge. The system is then oxidized or reduced to study the kinetics and spectroscopic properties of the resulting mixed valence compound. A classic example of these systems is seen in the Creutz-Taube ion, [(H3N)5Ru-pyrazine-

5+ 139 Ru(H3N)5] . An example of an M2 mixed valence system can be seen in the oxidation

t t 136 of the dimer-of-dimers complex, [( BuCO2)3Mo2(O2CCO2)Mo2( BuCO2)3]. In this system the oxalate bridge allows for communication between oxidized Mo2 centers leading to the formation of a class III, or fully delocalized mixed valent ion based on the

Robin and Day classification scheme.133 It is also possible to probe mixed valency by

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i reducing a M2 complex that has redox active ligands, such as M2(T PB)2[nic-B(C6F5)3]2

137 where M2 = Mo2 or W2 and nic = 4-isonicotinic acid. In this case rather than removing an orbital from a filled M2δ orbital, an electron is added to the Lπ* orbital leading to a mixed valent ion. A frontier molecular orbital diagram of these ions can be found below in Figure 6.1.

Figure 6.1. Frontier molecular orbital diagram of mixed valent ions of M2 compounds made by metal based oxidation (left)136 and ligand based reduction (right).137

i The discovery of mixed valency in M2(T PB)2(nic)2 compounds along with their ability to interact with Lewis acids such as B(C6F5)3 inspired the search for new “non-innocent” ligand systems that could be used for post synthetic modification. The ligand system described in this chapter is that of isonicotinate N-oxide, as seen in Figure 6.2. This

119 oxidized form of isonicotinate has a formal positive charge on nitrogen and a negative charge on oxygen. This negative charge is of interest because it could lead to different interactions with Lewis acids like boron. This Chapter will also report initial results of a film study utilizing isonicotinate N-oxide as an anchoring group for Mo2 paddlewheels for DSSC applications.

Figure 6.2. The three ligand systems discussed in this Chapter: Isonicotinate (red),

isonicotinate N-oxide (green), B(C6F5) adduct of isonicotinate N-oxide (blue).

6.2 Results and Discussion

6.2.1 Synthesis

i + - Compound 1, Mo2(T PB)2(O2CC5H4N -p-O )2, was synthesized by adding two

+ - i equivalence of HO2CC5H4N -p-O to a stirring toluene solution of Mo2(T PB)4. See

Scheme 6.1. The yellow solution slowly turned dark purple after several days and contained some precipitate. Some solvent was removed in vacuo resulting in more precipitate which was then filtered and washed several times with toluene and hexanes to remove starting material and H-TiPB acid. 1 was characterized using 1H NMR, UV-

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Visible spectroscopy and single crystal X-Ray crystallography. X-Ray quality crystals were obtained by slow diffusion of hexanes into a THF solution of 1.

Scheme 6.1. Synthesis of compound 1.

Upon isolation, 1 was dissolved in THF to form a dark red solution and two equivalents of B(C6F5)3 were added which immediately yielded a royal blue solution of compound 2,

i + - Mo2(T PB)2[O2CC5H4N -p-O-B (C6F5)3]2. See Scheme 6.2. This solution was examined using UV-Visible spectroscopy. Compound 2 was not isolated as the boron moiety dissociates in both THF and CH2Cl2 solutions after several hours. This bond cleavage could be due to ambient light and further attempts to isolate the product are currently underway.

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Scheme 6.2. Synthesis of compound 2.

n + + The cis compound 3 was synthesized by reacting two equivalents of Bu4N (O2CC5H4N -

- - 2+ - p-O ) with a stirring THF solution of cis-Mo2(DAniF)2(NCCH3)4 (PF6)2 . See Scheme

6.3. The solution immediately turned from yellow to red and was allowed to stir

n + overnight. The solution was then filtered through Celite to remove finely divided Bu4N

- PF6 . The THF was removed from the resulting solution and the red solid was washed multiple times with toluene and hexanes. After several purification attempts a small amount of the starting material remained in the final product.

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Scheme 6.3. Synthesis of compound 3.

6.2.2 Single Crystal X-Ray Structure

Dark red crystals of 1 were isolated through the slow evaporation of hexanes into a saturated THF solution. 1 crystallized in the monoclinic space group P21/c and contained one Mo2 molecule in the unit cell along with free THF solvent. A center of inversion was found in between the molecular Mo – Mo bond. The Mo2(O2C-R)4 core is unremarkable and consistent with other Mo2 paddlewheel complexes with Mo-Mo, and Mo-O bond distances ~2.1 Å.1 The TiPB moieties are significantly twisted out of conjugation with

o respect to their attending O2C units, with a torsion angle of 84 , effectively removing its electronic communication with the Mo2 core. The pyridyl N-oxide ligand however is not

o twisted with a torsion angle of only 8 which allows for extensive Lπ - Mo2δ - Lπ conjugation.103 A table of selected crystallographic parameters can be seen in Table 6.1 and an ORTEP representation of 1 can be seen in Figure 6.3.

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Figure 6.3. ORTEP representation of 1 shown at 50% probability. Hydrogens removed for clarity. Mo = Green, N = Blue, O = Scarlet, C = Gray.

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Compound 1 Chemical Formula C26H35MoNO6 Formula Weight 553.49 Temperature (K) 150(2) Space Group Monoclinic, P21/c a (Å) 14.2692(4) b (Å) 10.9533(2) c (Å) 18.2730(5)  (o) β (o) 112.7490(1)  (o) V (Å3) 2633.80(12) Z 4 Dcalcd (Mg/m3) 1.396 Crystal Size (mm) 0.38 X 0.27 X 0.12 Theta range for data collection 2.218 to 27.479o ,(Mo, K) (mm-1) 0.537 Reflections collected 35497 Unique reflections 6027 [R(int)= 0.037] Completeness to [θ] 100.0% [25.242] Data/restraints/parameters 6027 / 0 / 313 R1a (%) (all data) 3.44 (5.59) wR2b(%)(all data) 7.45 (8.18) Goodness-of-fit on F2 1.049 Largest diff. peak and hole (e Å-3) 0.841 and -0.641

aR1 =  | |Fo|-|Fc| | /  |Fo| 2 2 2 2 2 1/2 bwR2 = {  [w( Fo -Fc ) ] /  [ w(Fo ) ] }

Table 6.1. Select crystallographic parameters for 1

Perhaps the most noteworthy feature of the structural analysis of 1 is the molecular packing. In previous Chapters of this work, as well as numerous previous

125

19,130,134,140 reports, solvent molecules such as THF coordinate to the M2 axis. This is not the case in the structure of 1, as the metal-metal axis is coordinated by the N-oxide of the adjacent M2 paddlewheel. This intermolecular interaction causes the formation of a 2D coordination polymer with MM···O – N bond distances of 2.49 Å. This bond distance, along with the 2.12 Å Mo – Mo bond distance, indicates that this is likely a dative bond rather than a covalent bond which would require the oxidation of molybdenum. This interaction must be relatively strong compared to that of the solvent as there is THF found in the crystal lattice which fails to displace the MM···O – N bond. Two views of the extended structure of 1 can be seen below in Figure 6.4.

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Figure 6.4. Extended structure of 1 which propagates parallel to the crystallographic b and c axes. TiPB moieties and solvent removed for clarity.

6.2.3 Electronic Absorption Studies

i The electronic absorption spectra comparing Mo2(T PB)2(nic)2, 1 and 2 in THF at room temperature are shown in Figure 6.5. Solutions of 1 and 2 give an intense red or blue

1 color respectively which arise from a fully allowed MLCT transition from the Mo2δ to benzoate π*. These absorptions occur at 500 nm for 1 and 665 nm for 2. The cause of the red shift in the boron adduct will be discussed in detail in the upcoming sections. The effect oxidation of nic has on the MLCT transition is also of interest. The absorption band

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i of Mo2(T PB)2(nic)2 presents at 475 nm which red shifts to 500 nm when the pyridyl N- oxide is used.137 The nature of this shift will also be discussed further in the next section.

i Figure 6.5. Electronic absorption spectra of Mo2(T PB)2(nic)2, 1 and 2 in THF at room temperature.

6.2.4 Electronic Structure Calculations

i To interpret the trends seen in the electronic absorption spectra of Mo2(T PB)2(nic)2, 1 and 2, DFT calculations were employed on model compounds. Due to the twisting of the

i T PB moiety out of conjugation with the M2 unit, seen in the structural analysis, it is assumed that it will have little influence on the electronic structure and was therefore replaced with formate. This assumption saves on computational resources by allowing for idealized symmetry and reduces the number of degrees of freedom in the molecule. The

128 model compounds of 1 and 2 are 1’ and 2’ respectively. The boron adduct 2’ is also simplified to BF3 as calculations involving the B(C6F5)3 moiety were unstable. The

i energy levels of the previously reported Mo2(T PB)2(nic)2 will also be discussed and has been modeled as Mo2(O2CH)2(nic)2.

Compounds 1’ and 2’ can be thought of as extension of the parent complex

Mo2(O2CH)2(nic)2 with subsequent oxidation (1’) and boronation (2’). As such the discussion of electronic structure must derive from first understanding the orbital contributions of Mo2(O2CH)2(nic)2. The HOMO level appears at -5.48 eV and is Mo2δ based. The Mo2π and Lπ orbitals are notably much lower in energy, lying between -7 and

-7.5 eV appearing The LUMO is Lπ* in nature and the HOMO – LUMO gap is 3.25 eV.

The LUMO+1 orbital lies slightly above the LUMO and is Mo2δ* in character.

Upon oxidation of the pyridyl ligands to form 1’ the Mo2δ orbital is destabilized, causing a rise in the HOMO of 0.15 eV. While this orbital is primarily Mo2δ in nature it is also important to note that there is significant ligand character and O- p-orbital character in particular. The Lπ* based LUMO was also seen to decrease in energy by 0.12 eV which ultimately leads to a HOMO – LUMO gap of 2.98 eV, nearly 0.25 eV less than the parent. A GaussView9 plot of the HOMO and LUMO of 1’ can be seen below in Figure

6.6.

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Figure 6.6. GaussView9 plots of the HOMO and LUMO level of 1’drawn at isovalue 0.03.

The change in energy seen in the frontier molecular orbitals of 1’ explains the red shift of its absorption spectrum by ~25 nm. The reason for this orbital perturbation likely stems from the higher energy pyridyl N-oxide ligand orbitals, which allows for more mixing between the metal and the ligand and consequently causes an increase to the Mo2δ based

HOMO. The higher Lπ energy can also be seen in the drastic increase in energy of the

HOMO-1 and HOMO-2 orbitals. The energy of these orbitals is increased by nearly 1 eV from the parent compound.

Calculations of the boron adduct 2’ showed a dramatic decrease in energy of the HOMO orbital by 1 eV. The Lπ* based LUMO also decreased in energy by 1.25 eV to yield a

HOMO – LUMO gap 2.72 eV. The previously destabilized Lπ orbitals seen in 1’ were greatly stabilized by the addition of boron forming a tight band around -8 eV. An energy

130 level diagram comparing the frontier molecular orbitals of Mo2(O2CH)2(nic)2, 1’ and 2’ can be seen below in Figure 6.7.

Figure 6.7. Frontier molecular orbital diagram comparing Mo2(O2CH)2(nic)2, 1’ and 2’

6.2.5 Film Studies

The facile reaction of 1 with B(C6F5)3 to form 2 along with 1’s propensity to form coordination polymers in the solid state suggests that the pyridyl N-oxide ligand of 1 is quite nucleophilic. This affinity for Lewis acids makes Mo2 paddle wheels containing

131 pyridyl N-oxides excellent candidates for adsorption onto a metal based semiconductor.

As discussed in the introductory Chapter of this work, anchoring groups for DSSCs are typically carboxylic acids. This bonding motif in Mo2 based systems was previously investigated by Dr. Samantha Brown-Xu and coworkers. The cis dimolybdenum

2- n + compound Mo2(DAniF)2(TTh-CO2) ( Bu4N)2 (4) is able to bind to TiO2 and was shown

17 to undergo charge injection into TiO2 nanoparticles upon excitation. A diagram of 4 can be seen below in Scheme 6.4.

17 Scheme 6.4. The first Mo2 dye for DSSC applications.

In light of this discovery compound 3 was synthesized. The cis geometry of 3 combined with the non-innocent N-oxide moiety is ideal for binding to TiO2 nanoparticles and other semiconducting materials like NiO and indium-tin oxide (ITO). To test the binding affinity of 3, thin films of TiO2, NiO and ITO films were made on conductive glass.

These slides can be seen below in Figure 6.8.

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Figure 6.8. The nine metal-oxide films, prior to the dye loading study along with their corresponding thicknesses (Note: Bright white spot on lower left film is from reflection).

Each glass slide was then allowed to soak overnight in a vial containing a 0.02 mM solution of 3 in CH2Cl2. The slides were then removed from the dye solution and washed several times with fresh CH2Cl2 to remove any dye that had not adhered to the material.

A UV-visible spectrum was taken of the soak solution before and after addition of the films to determine the degree to which the dye had adsorbed. A digital photograph was

133 also taken to document the gross changes to the film after 12 hours of soaking. A diagram describing the experimental set up along with the proposed binding mode can be seen below in Figure 6.9.

Figure 6.9. Pictorial representation of the dye loading experiment in a CH2Cl2 solution of 3 (top), and the proposed bonding mode of the dye on a semiconductor surface (bottom).

In all cases there is a marked drop in the intensity of the soak solution after soaking for

12 hours. By noting the percent change in the intensity of the MLCT band before and after soaking it is possible to determine the relative percent loading of the dye. TiO2 was 134 found to load between 45 - 52% of the stock solution, NiO had a loading of ~ 37% and

ITO showed a loading percentage of ~32%. The decrease in MLCT intensity is unlikely to be caused by decomposition of the dye as the film studies were carried out in a nitrogen filled glove box, and 3 is stable at room temperature in the solvent CH2Cl2. The gross features of the films also serve as evidence that the dye has adsorbed. There is a striking difference between the TiO2 films before and after soaking as the material goes from bright white to deep violet in color. It is also possible to see this color change in the case of ITO where the formerly yellow film is turned light purple after 12 hours in a solution of 3. The UV-Visible traces of the soak solution before and after addition of the semiconductor films along with digital photographs of the final films can be seen below in Figures 6.10 – 6.12.

Figure 6.10. Absorption of a 0.02 mM solution of 3 before and after loading onto TiO2 (left) and a picture of the TiO2 film after 12 hours of soaking (right).

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Figure 6.11. Absorption of a 0.02 mM solution of 3 before and after loading onto NiO (left) and a picture of the NiO film after 12 hours of soaking (right).

Figure 6.12. Absorption of a 0.02 mM solution of 3 before and after loading onto ITO (left) and a picture of the ITO film after 12 hours of soaking (right).

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6.3 Conclusion

Three new Mo2 paddle wheels have been synthesized and characterized. The addition of a pyridyl N-oxide group shows a significant red shift to the absorption spectra compared to the unoxodized species. This red shift is due to the perturbation of the electronic structure, and specifically the destabilization of the Mo2δ based HOMO. Compound 1 was shown to have an affinity for Lewis bases such as B(C6F5)3, as well as its own Mo2 axis, which was seen in the x-ray structure. This affinity was used to successfully adsorb the cis complex 3 onto the surface of three different semiconducting materials, TiO2,

NiO, and ITO. This initial data suggests that Mo2 paddlewheels could potentially be used as DSSC dyes by anchoring them to solid state surface with N-oxide ligands. This discovery could have wide ranging applications in other dyes as pyridyl N-oxides have not received a great deal of attention as anchoring groups to this point. Construction of working DSSCs with dye 3 are currently underway.

6.4 Experimental

6.4.1 Synthesis n + + - - + - Bu4N [O2CC5H4N -p-O ] HO2CC5H4N -p-O ( 200 mg, 1.44 mmol) was suspended in

n 10 mL of MeOH and Bu4NOH 1M in MeOH (1.44 mL, 1.44 mmol) was slowly added.

The solution became clear and was allowed to stir overnight. The solvent was then

1 removed under vacuum yielding an off white solid. H NMR (CDCl3, 400 MHz): H 8.04

(d, 2H), 7.87 (d, 2H), 3.27 (m, 9H), 1.60 (m, 9H), 1.36 (m, 9H), 0.92 (t, 14H).

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i + - + - Mo2(T PB)2(O2CC5H4N -p-O )2 (1). HO2CC5H4N -p-O (47 mg, 0.338 mmol) and

Mo2(TiPB)4 (200 mg, 0.169 mmol) were added to a Schlenk flask containing 20 mL of toluene and allowed to stir. After 3 days a dark red precipitate formed. The precipitate was filtered and washed with toluene (3 x 20 mL) and hexanes (2 X mL). 1H NMR (THF- d8, 400 MHz): H 8.29 (d, 4H, JHH = 7.1 Hz), 8.12 (d, 4H, JHH = 7.1 Hz), 7.04 (s, 4H),

3.03 (m, 4H), 2.89 (m, 2H) 1.25 (d, 12H, JHH = 7.1 Hz), 1.10 (d, 24H, JHH = 7.1 Hz). UV-

Vis (in CH2Cl2, 293K) 503, 315 nm.

+ - 2+ - cis-Mo2(DAniF)2(O2CC5H4N -p-O )2 (3). Mo2(DAnif)2(NCCH3)4 (PF6 )2 (62 mg, 0.062 mmol) was dissolved in 10 mL of acetonitrile and added to a stirring solution of n + + - - Bu4N [O2CC5H4N -p-O ] (45 mg, 0.12 mmol) yielding a red precipitate. The solid was filtered and washed with toluene (3 X 20 mL) and hexanes (2 X 20 mL).

6.2.2 Film Preparation

The author thanks Mr. Damian Beauchamp for expertly preparing the metal oxide films for this chapter.

All metal oxide films were deposited on to fluorine doped tin oxide (FTO) (Hartford

Glass Co., Inc) conductive glass substrates via a doctor blade method and annealed in an oven (ramp rate = 5oC; target temp = 450oC; annealing time = 30 min; allowed to cool to r.t. naturally with oven door shut). The doctor blade method used double layered scotch tape with a circular hole punched out of diameter 0.28 cm2. The scotch tape was then applied to the glass substrate to which was dropped 15 μL of the corresponding metal oxide paste and deposited above the exposed glass on the scotch tape. The paste was then pulled over the exposed glass with a glass slide (which acted as the "squeegee"). The 138 doctor bladed paste was allowed to dry covered with a petri dish top (20 min), the tape was removed, and the resulting film annealed in air (conditions above). All film thicknesses were measured via Alpha-Step D-100 Profilometer (KLA-Tencor).

Nickle oxide paste preparation. Standard precursor solutions of NiO were prepared by dissolving anhydrous NiCl2 (100 mg, Sigma) and the triblock co-polymer (30 mg, Sigma) into a mixture of Milli-Q water (300 mg) and ethanol (600 mg, Fisher). The solution was left at rest for 3 days at 30oC, and then centrifuged. Obtained supernatant solution was used as the paste.141,142

Indium tin oxide and Titanium dioxide paste preparation. - 1.2 g of commercial TiO2

(titanium dioxide P25, Aeroxide) or ITO nanopowder (indium tin oxide, NanoTek,

99.5%, Alfa Aesar) was dispersed in 10 ml ethanol via sonication. 2 mL of 10 w.t.% ethyl cellulose ethanolic solution and 4 ml terpineol were added to the initial suspension.

After a homogeneous paste was obtained, ethanol was removed from the paste on a rotary evaporator.

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CHAPTER 7 : CRYSTAL ENGINEERING OF Mo2 UNITS THROUGH HALOGEN-

HALOGEN INTERACTIONS

Adapted from a 2015 publication in Inorganica Chimica Acta130

7.1 Introduction

Single crystal X-Ray analysis of Mo2 carboxylates has been discussed in various chapters of this work to determine ligand disposition, i.e. trans vs. cis, and the degree of ligand conjugation with the metal center, through the study of torsion angles. In many cases of

Mo2 carboxylates the gross anatomy of the molecular structure along with bond lengths and angles are the most useful information gleaned from X-Ray analysis. In some instances, however, the packing of the molecules in the crystal lattice can be of considerable interest. One instance of this was seen in the previous chapter in the

i discovery of the 2D polymer formed by Mo2(T PB)2(O2CC5H4-p-NO)2. Another classic example of molecular laddering along the M2 z-axis can be seen in the homoleptic

143 compound, Mo2(O2C-C6H5)4, seen in Figure 7.1. Here it is evident that the oxygen of each neighboring carboxylate binds to the M2 z-axis to form a 1D coordination polymer.

140

130 Figure 7.1. Molecular ordering by Mo2···O interactions in Mo2(O2C-C6H5)4.

In this Chapter a family of para-halobenzoate Mo2 compounds will be discussed that show an alternate form of molecular ordering, through halogen-halogen interactions. The nature of these interactions is based on the type of molecule, i.e. bis-bis vs. homoleptic, and the choice of halogen. Understanding the packing of these molecules and the influence the halogen has on molecular ordering could lead to more intelligent material design of M2 carboxylate materials in the future.

7.2 Results and Discussion

7.2.1 Synthesis

The homoleptic compounds 1-X (Where X = F, Cl, Br, or I) were prepared by refluxing

Mo(CO)6 and the appropriate p-halobenzoic acid in a solution of 1,2-dichlorobenzene.

The resulting precipitate was then filtered and washed with copious amounts of hexanes.

The bis-bis compounds 2-X (where X = F, Cl, Br, or I) were prepared by allowing two 141 equivalents of the appropriate p-halobenzoic acid to stir in a toluene solution with one

i equivalents of Mo2(T PB)4. The precipitate that formed after three days was filtered and washed with toluene and hexanes. See Scheme 7.1.

All of the new compounds were yellow or yellow-orange and were soluble in THF, and slightly soluble in toluene. All eight compounds were characterized using 1H NMR and

MALDI-TOF. X-Ray quality crystals were grown of 1-X (X = F, and Cl) and 2-X (X = F,

Cl, Br, and I).

Scheme 7.1. Synthesis of supported p-halobenzoate Mo2 homoleptic and bis-bis complexes, where X = F, Cl, Br, and I.

7.2.2 Steady State Electronic Spectroscopy

In order to investigate the effects of a given halide on the electronic structure of compounds 1-X and 2-X UV-Visible spectroscopy was conducted. All measurements were conducted on dilute solutions of THF at room temperature. The plots of 1-X and 2-

X can be seen below in Figure 7.2.

The homoleptic compounds, 1-X, show essentially one peak presenting between 400 –

500 nm. This is due to a fully allowed metal-to-ligand charge-transfer (MLCT) which primarily involves a Mo2δ to halobenzoate π* transition. Aside from this intense, broad peak there is little else of interest concerning the homoleptic series except for the ligand π

142

– π* transitions at high energy (~250 nm) which are largely out of the experimental window.

The bis-bis compounds, 2-X, also show MLCT bands from 400 – 500 nm and π – π* transitions at high energy. In addition these compounds have less intense bands from 300

i – 350 nm which correspond to the Mo2δ to O2C-T PB π* transition. The reason for this band appearing at higher energy due to the twisting of the TiPB moiety has been described in previous chapters.

Figure 7.2. Electronic absorption spectrum of families 1-X (Top) and 2-X (Bottom) taken in THF at room temperature.

143

The MLCT bands in both cases tend to shift to lower energy as we decend the periodic table following the trend: F > Cl > Br > I. Upon excitation into their respective MLCT bands, each of the compounds showed S1 fluorescence in the visible region which tracks with the trends seen in the absorption spectroscopy. See Figure 7.3. In addition, each compound showed phosphorescence centered around 1100 nm which correlates to a T1

MoMoδδ* state. See appendix.

Figure 7.3. Fluorescence spectra of families 1-X (Top) and 2-X (Bottom) taken in THF at room temperature upon excitation into the MLCT absorption band.

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7.2.3 Solid State Structures

Single crystals suitable for single crystal X-Ray analysis of 1-X (X = F, Cl) and 2-X (X =

F – I) were grown by slow diffusion of hexanes into a moderately concentrated THF solution. 1-Br and 1-I failed to yield sufficient crystals after numerous attempts to obtain them. Typically these derivatives formed long thin rods or thin plates.

ORTEP representations of each structure, drawn at 50% probability, can be seen below in

Figure 7.4 and selected crystallographic metrics can be seen in Tables 7.1 - 7.3.

Compounds 1-F, 2-F and 2-Cl crystallized in the monoclinic space group P21/c each containing two molecules in the unit cell. The remaining three structures, 1-Cl, 2-Br and

2-I crystallized in the triclinic space group P-1 each containing one molecule in the unit cell. In all cases the complete Mo2 dimer is generated by an inversion center in between the M-M bond. The data quality of all structures was excellent with diffraction out to 27o of θ.

In general, the bond distances and angles of the Mo2(O2C-R)4 cores are unremarkable and are similar to those previously reported in this work and the literature.1 In compounds 2-

X attending TiPB moieties are twisted nearly 90o out of conjugation with the core, while the trans phenylhalides are coplanar with their respective O2C moieties.

145

Figure 7.4. ORTEP drawings of 1 (F,Cl) and 2 (F – I) drawn at 50% probability. Solvent and hydrogen atoms removed for clarity.

146

Compound 1 - F 1 - Cl

Chemical formula C36H32F4Mo2O10 C36H32Cl4Mo2O10 Formula weight 892.49 958.29 Temp (K) 150(2) 150(2)

Space group Monoclinic, P21/c Triclinic, P-1 a (Å) 9.4977(1) 6.7473(1) b (Å) 18.0339(4) 11.6194(2) c (Å) 11.0316(2) 12.1291(3) α ( o ) 95.576(1) β ( o ) 110.952(1) 99.128(1) γ ( o ) 100.377(1) V (Å3) 1764.57(5) 915.74(3) Z 2 1 Dcalcd (Mg/m3) 1.680 1.738 Crystal size (mm) 0.38 X 0.19 X 0.15 0.27 X 0.12 X 0.12 Theta range for data collection (o) 2.259 to 27.460 1.715 to 27.472 ,(Mo, K) (mm-1) 0.789 1.034 Reflections collected 33362 28066 Unique reflections 4038 [R(int)= 0.030] 4201 [R(int)=0.030] Data Completeness to [ θ ] 100.0% [ 25.242 ] 100.0% [ 25.242 ] Data/restraints/parameters 4038 / 0 / 235 4201 / 0 / 235 R1a (%) (all data) 3.27 (4.43) 2.74 (3.67) wR2b (%)(all data) 8.74 (10.09) 7.29 (9.60) Goodness-of-fit on F2 1.165 1.276 Largest diff. peak and hole (e Å-3) 0.946 and -0.670 0.851 and -1.032

aR1 =  | |Fo|-|Fc| | /  |Fo| x 100 bwR2 = [w ( Fo2-Fc2 )2 /  (w |Fo|2)2]1/2 x 100

Table 7.1. Select crystallographic parameters for homoleptic compounds 1 – (F, Cl)

147

Compound 2 - F 2 - Cl

Chemical formula C54H70F2Mo2O10 C54H70Cl2Mo2O10 Formula weight 1108.98 1141.88 Temp (K) 150(2) 152(2)

Space group Monoclinic, P21/c Monoclinic, P21/c a (Å) 10.1027(2) 10.5454(3) b (Å) 15.2966(4) 28.4540(9) c (Å) 17.1975(4) 10.0650(3) α ( o ) β ( o ) 94.985(2) 115.025(1) γ ( o ) V (Å3) 2647.60(11) 2736.57(14) Z 2 2 Dcalcd (Mg/m3) 1.391 1.386 Crystal size (mm) 0.38X0.38X 0.23 0.38X0.23X0.19 Theta range for data collection (o) 2.378 to 27.454 1.431 to 27.438 ,(Mo, K) (mm-1) 0.536 0.610 Reflections collected 46777 40716 Unique reflections 6037 [R(int)= 0.049] 6237 [R(int)=0.051] Data Completeness to [ θ ] 99.9% [ 25.242 ] 100.0% [ 25.242 ] Data/restraints/parameters 6037 / 15 / 307 6237 / 0 / 307 R1a (%) (all data) 3.65 (5.25) 4.41 (7.12) wR2b (%)(all data) 8.85 (9.98) 10.91 (12.65) Goodness-of-fit on F2 1.079 1.101 Largest diff. peak and hole (e Å-3) 0.736 and -0.505 1.534 and -0.595

aR1 =  | |Fo|-|Fc| | /  |Fo| x 100 bwR2 = [w ( Fo2-Fc2 )2 /  (w |Fo|2)2]1/2 x 100

Table 7.2. Select crystallographic parameters for bis-bis compounds 2 – (F-Cl)

148

Compound 2 - Br 2 - I

Chemical formula C54H70Br2Mo2O10 C54H70I2Mo2O10 Formula weight 1230.80 1324.78 Temp (K) 150(2) 150(2) Space group Triclinic, P-1 Triclinic, P-1 a (Å) 10.0697(2) 10.0917(3) b (Å) 10.5101(2) 10.4630(2) c (Å) 14.8323(2) 14.7965(4) α ( o ) 73.389(1) 76.668(2) β ( o ) 80.287(1) 86.366(1) γ ( o ) 64.104(1) 65.537(2) V (Å3) 1351.45(4) 1382.87(7) Z 1 1 Dcalcd (Mg/m3) 1.512 1.591 Crystal size (mm) 0.27X 0.19 X 0.15 0.31X 0.27 X 0.19 Theta range for data collection (o) 1.435 to 27.475 1.415 to 27.426 ,(Mo, K) (mm-1) 1.997 1.623 Reflections collected 35192 35285 Unique reflections 6194 [R(int)=0.048] 6286 [R(int)=0.041] Data Completeness to [ θ ] 99.9% [ 25.242 ] 100.0% [ 25.242 ] Data/restraints/parameters 6194 / 0 / 307 6286 / 0 / 307 R1a (%) (all data) 3.76 (6.17) 3.81 (6.35) wR2b (%)(all data) 9.0 (11.9) 9.41 (12.77) Goodness-of-fit on F2 1.12 1.116 Largest diff. peak and hole (e Å-3) 0.90 and -1.47 2.111 and -0.969

aR1 =  | |Fo|-|Fc| | /  |Fo| x 100 bwR2 = [w ( Fo2-Fc2 )2 /  (w |Fo|2)2]1/2 x 100

Table 7.3. Select crystallographic parameters for bis-bis compounds 2 – (Br - I)

149

7.2.4 Crystal Packing

Of the two homoleptic compounds that crystallized, the fluoro- compound, 1-F, packed as discrete molecules, having no predisposition for any noteworthy arrangement. THF was coordinated axially and the packing is presumably dictated by van der waals forces rather than π – π stacking or halogen – halogen interactions. Compound 1 – Cl, however, adopted a much different packing mode. 1-Cl shows a laddering effect where each Cl interacts with an adjacent Cl in a neighboring molecule. This Cl – Cl interaction propagates in only one direction with one Cl interacting with just one other Cl. This

●●● halogen – halogen interaction yields Cl – Cl distances of 3.30 Å and C-X X’, C’-X’

●●● o o X angles of 176.2 and 85.1 respectively. The Cl – Cl laddering effect of 1 – Cl can be seen in Figure 7.5.

150

Figure 7.5. Halogen – Halogen interactions in 1-Cl showing Cl – Cl laddering.

The trans substituted compounds, 2-X, show several forms of packing. When X = Br or I we observe halogen-halogen interactions from one unit to the next, again, forming a one dimensional chain. The X – X distances are 3.80 Å for iodine and 3.59 Å for bromine.

The manner in which these halogens interact is also interesting. In the case of I – I the molecules slip to the side of one another, along the MM axis, while Br – Br slip vertically along the axis of the TiPB ligands. An ORTEP drawing of these interactions can be seen below in Figures 7.6 and 7.7.

151

Figure 7.6. Halogen – Halogen interactions in 2-Br showing a Br – Br slip in the vertical direction.

Figure 7.7. Halogen – Halogen interactions in 2-I showing an I – I slip in the horozontal direction.

152

It is interesting to note that the chlorobenzoate derivative shows no halogen-halogen interactions like those that were so striking in 1-Cl. This could be due to the Cl – Cl interaction being weaker than that seen in Br and I requiring two bonds to pattern the molecules rather than just one. In the case of the fluorobenzoate derivative, 2-F, while there are no halogen-halogen interactions, there is considerable π – π stacking, seen in

Figure 7.8. The distance between adjacent fluorobenzoate moieties is ~ 4 Å and show no

F – F interactions.

Figure 7.8. π – π stacking seen in the crystal packing of 2-F. 153

●●● Until this point crystal packing in M2 tetracarboxylates has been limited to the Mo O interactions discussed earlier in this chapter and, occasionally, π – π stacking between conjugated organic ligands. Crystal engineering with these halogen – halogen interactions allow for a new avenue in templating M2(O2C-R)4 molecules for a variety of uses. In general we see that heavier elements lead to more favorable halogen – halogen interactions such that I – I > Br – Br > Cl – Cl >> F – F. In organic systems these X – X

●●● ●●● interactions fit into two classes based on the two C-X X angles, C-X X’ and C’-

●●● ●●● ●●● X’ X illustrated below in Figure 7.9. In general if C-X X’ and C’-X’ X are

●●● ●●● equal the interaction is said to be type 1, and if C-X X’ is nearly linear and C’-X’

X is approaching 90o the interaction is said to be type 2.144 Interactions of this kind have been seen in a wide range of materials and in crystal engineering.145–149 The various packing forms of compounds 1-F, 1-Cl, and 2-X are summaries below in Table 7.4.

Figure 7.9. General form of type 1 and type 2 halogen – halogen interactions.

154

●●● Table 7.4. Summary of crystallographic C-X X angles and their respective interactions.

7.3 Conclusion p-halobenzoates have been incorporated into the MM paddlewheel. The two new families of compounds have been synthesized and characterized unambiguously. The absorption and emission spectra show a modest dependence on the chosen halogen.

The solid state analysis of these compounds showed that the choice of halide affects the molecular packing. The homoleptic compounds 1-F and 1-Cl showed differing behavior, with 1-F packing as discrete molecules and 1-Cl ordering in a way that maximized type 2 halogen – halogen interactions. The bis-bis compounds 2-X showed several different packing modes, with 2-Cl forming discrete molecules, 2-F showing π – π stacking and 2-

Br/2-I adopting type 1 halogen – halogen interactions. The discovery of these packing arrangements now allows for crystal engineering of M2 paddlewheel complexes which could be useful when fabricating devices.

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7.4 Experimental

7.4.1 Synthesis

General Synthesis of 1-X. Mo(CO)6 and two equivalents of the respective carboxylic acid were placed into a Schlenk flask and 4:1 o-dichlorobenzene:THF mixture [10-15 mL total]. The mixture was heated to reflux [~140 °C] for 48 hours. Upon cooling, the THF was removed under vacuum and the product precipitated from solution. The desired product was isolated as a microcrystalline powder by filtration and washing with hexanes

[3 x 15 mL].

i General Synthesis of 2-X. Mo2(T PB)4 and two equivalents of the desired carboxylic acid were combined in a Schlenk flask and dissolved in toluene [10-15 mL]. The reaction mixed at room temperature for 48 hours where a precipitate formed. The desired product was isolated by filtration as a powder and was further purified by washings with hexanes

[3 x 15 mL].

1-F. Mo(CO)6 [250 mg, 0.95 mmol] and 4-fluorobenzoic acid [268 mg, 1.91 mmol] produced Mo2(PhF)4 [345 mg, 97%]. NMR (DMSO-d6): δH (400 MHz) 8.23 (dd, 8H, JHH

= 8.4 Hz, JHF = 5.3 Hz), 7.38 (t, 8H, JHH = 8.8 Hz, JHF = 8.8 Hz). MALDI-TOF MS:

C28H16F4Mo2O8 Calculated: 751.9, Found: 747.0.

1-Cl. Mo(CO)6 [250 mg, 0.95 mmol] and 4-chlorobenzoic acid [304 mg, 1.95 mmol] produced Mo2(PhCl)4 [370 mg, 96%]. NMR (DMSO-d6): δH (400 MHz) 8.16 (d, 8H, JHH

= 8.6 Hz), 7.60 (d, 8H, JHH = 8.6 Hz). MALDI-TOF MS: C28H16Cl4Mo2O8 Calculated:

815.8, Found: 812.9.

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1-Br. Mo(CO)6 [250 mg, 0.95 mmol] and 4-bromobenzoic acid [398 mg, 1.98 mmol] produced Mo2(PhBr)4 [410 mg, 87%]. NMR (THF-d8): δH (400 MHz) 8.13 (d,

8H, JHH=8.5 Hz), 7.63 (d, 8H, JHH=8.5 Hz). MALDI-TOF MS: C28H16Br4Mo2O8

Calculated: 991.6, Found: 990.9.

1-I. Mo(CO)6 [250 mg, 0.95 mmol] and 4-iodobenzoic acid [470 mg, 1.90 mmol] produced Mo2(PhI)4 [510 mg, 91%]. NMR (THF-d8): δH (400 MHz) 7.96 (d, 8H, JHH=

8.0 Hz), 7.74 (d, 8H, JHH=8.2 Hz). MALDI-TOF MS: C28H16I4Mo2O8 Calculated: 1183.5,

Found: 1179.9.

i 2-F. Mo2(T PB)4 [100 mg, 0.085 mmol] and 4-fluorobenzoic acid [24 mg, 0.171 mmol]

i produced Mo2(T PB)2(PhF)2 [55 mg, 67%]. NMR (THF-d8): δH (400 MHz) 8.40 (dd, 4H,

J = 8.4, 5.6 Hz), 7.31 (t, 4H, J = 5.6 Hz) 7.00 (s, 4H), 3.03 (sep, 4H, JHH = 6.9 Hz), 2.87

(sep, 2H, JHH = 6.9 Hz), 1.23 (d, 12H, JHH = 6.9 Hz), 1.03 (d, 24H, JHH = 6.9 Hz).

MALDI-TOF MS: C46H54F2Mo2O8 Calculated: 968.2, Found: 965.2.

i 2-Cl. Mo2(T PB)4 [200 mg, 0.17 mmol] and 4-chlorobenzoic acid [52.8 mg, 0.34 mmol]

i produced Mo2(T PB)2(PhCl)2 [132 mg, 78%]. NMR (DMSO-d6): δH (400 MHz) 8.34 (d,

4H, JHH = 8.5 Hz), 7.60 (d, 4H, JHH = 8.5 Hz), 7.00 (s, 4H), 3.02 (sep, 4H, JHH = 6.8 Hz),

2.87 (sep, 2H, JHH = 6.8 Hz), 1.23 (d, 12H, JHH = 6.8 Hz), 1.03 (d, 24H, JHH = 7.0 Hz).

MALDI-TOF MS: C46H54Cl2Mo2O8 Calculated: 1000.0 Found: 997.6.

i 2-Br. Mo2(T PB)4 [600 mg, 0.51 mmol] and 4-bromobenzoic acid [195 mg, 0.97 mmol]

i produced Mo2(T PB)2(PhBr)2 [483 mg, 87%]. NMR (DMSO-d6): δH (400 MHz) 8.26 (d,

4H, JHH = 8.6 Hz), 7.77 (d, 4H, JHH = 8.6 Hz) 7.01 (s, 4H), 3.02 (sep, 4H, JHH = 6.6 Hz),

157

2.88 (sep, 4H, JHH = 6.6 Hz), 1.24 (d, 12H, JHH = 6.6 Hz), 1.04 (d, 24H, JHH = 6.6 Hz).

MALDI-TOF MS: C46H54Br2Mo2O8 Calculated: 1088.0 Found: 1085.7.

i 2-I. Mo2(T PB)4 [200 mg, 0.17 mmol] and 4-iodobenzoic acid [84 mg, 0.34 mmol]

i produced Mo2(T PB)2(PhI)2 [155 mg, 75%]. NMR (THF-d8): δH (400 MHz) 8.09 (d, 4H,

JHH = 8.4 Hz), 7.97 (d, 4H, JHH = 8.4 Hz), 7.00 (s, 4H), 3.01 (sep, 4H, JHH = 7.5 Hz ), 2.87

(sep, 6H, JHH = 7.0 Hz), 1.23 (d, 12H, JHH = 7.0 Hz), 1.03 (d, 24H, JHH = 7.0 Hz).

MALDI-TOF MS: C46H54I2Mo2O8: Calculated: 1184.0, Found: 1181.5.

7.4.2 Single Crystal X-Ray Diffraction

Single crystals of 1 – (F, Cl) and 2 – (F-I) were isolated and handled under a pool of fluorinated oil. Examination of the diffraction pattern was done on a Nonius Kappa CCD diffractometer with Mo Kα radiation. All work was conducted at 150 K using an Oxford

Cryosystems Cryostream Cooler. Data integration was performed with Denzo, and scaling and merging of the data was done with Scalepack.150 The structures were solved by the direct methods program in SHELXS-13.151 Full-matrix least-squares refinements based on F2 were performed in SHELXL-13,151 as incorporated in the WinGX package.152 For each methyl group, the hydrogen atoms were added at calculated positions using a riding model with U(H) = 1.5Ueq (bonded carbon atom). The rest of the hydrogen atoms were included in the model at calculated positions using a riding model with U(H) = 1.2Ueq (bonded atom). Neutral atom scattering factors were used and include terms for anomalous dispersion.153

158

CCDC 1011284-1011289 contains the supplementary crystallographic data for this paper.

These data can be obtained free of charge from The Cambridge Crystallographic Data

Center via www.ccdc.cam.ac.uk/data_request/cif.

159

CHAPTER 8 : FINAL PERSPECTIVES AND FUTURE DIRECTIONS

Over the last several chapters of this work the effect of transition metals, semi-conducting surfaces, and halogens on the M2 paddlewheel complex has been investigated and discussed. Transition metals, and metal carbonyl moieties in particular, have been shown to greatly influence the electronic structure of M2 units. The implementation of additional d-orbitals allows for more optical transitions that can be used to tune and cover more of the solar spectrum. These mixed metal compounds show attractive properties that could be used to enhance the efficiency of next generation solar harvesting materials or even act as photocatalysts in the future.

The findings of Chapter 3 suggest that organometallic ligands in conjunction with M2 paddlewheels can lead to very interesting results. While chromium carbonyl ligands have a propensity to lose CO and thus may not be ideal candidates to use in a solar cell, they have proved to be good test beds for a new type of ligand and a vital proof-of-concept.

The two bis-bis complexes that were synthesized and characterized in this chapter,

i 6 namely M2(T PB)2[O2C-C6H5-η -Cr(CO)3]2 where M2 = Mo2 or W2, ended up showing very different excited state features. This difference stems from the fact that Mo2δ

160 orbitals are lower in energy than their tungsten counterparts and are capable of mixing with the ligand Cr d-orbitals. This admixture complicates the excited state infrared features. None the less it was possible to see an initial 1MLCT state which leads to a 3δδ* state. In the case of tungsten these excited state features are much easier to follow and show a 1MLCT state intersystem crossing to a 3MLCT which is evident by the CO stretches shifting to lower energy. Ultimately, the concept of using metal carbonyls as organometallic ligands proved to be quite enlightening and lead to the development of other metal carbonyl systems such as the one seen in Chapter 4. Along with being interesting from a synthetic point of view, the CO stretches were excellent IR markers and were remarkably sensitive to electronic perturbation in the excited state. Further work on this chapter would include determining the true nature of the photoproduct formed when the molybdenum complex is irradiated in a THF solution.

After showing that chromium carbonyls give rise to interesting spectroscopic and electronic properties in Chapter 3, a new ligand was designed to explore the effect of

Re(CO)3Cl on the metal-metal bond. As monocarboxylic acid bipyridyls are difficult synthetic targets, the new rhenium based ligand Re(PMT-H)(CO)3Cl was developed. The

Re(CO)3Cl fragment was found to have a profound effect on the electronic structure of

i the final bis-bis compound Mo2(T PB)2[PMTRe(CO)3Cl]2. Rhenium metal served to

i greatly stabilize the HOMO and LUMO of the parent compound, Mo2(T PB)2(PMT)2 due to its large electron withdrawing effect. This caused a drastic red shift in the MLCT band yielding a blue compound. DFT calculations showed that the HOMO level consists of mostly Re character rather than the typical Mo2δ orbital. However, upon chemical

161 oxidation, the EPR spectrum suggests that the hole remains on the Mo2 metal center rather than on the Re ligands. This can be explained by either a redistribution of charge after oxidation or an initial oxidation of the Mo2δ orbital due to the kinetic accessibility of the MM axis. The excited state features of the resulting molecules suggests a delocalized 1MLCT state that intersystem crosses to a long lived 3δδ* state. There are many directions this project could take in the future as the PMT-H ligand is quite versatile. Many different metals could be chelated and attached to the M2 core to further investigate the role of secondary metals. While Re(PMT-H)(CO)3Cl served as an excellent ligand in this investigation it should also be investigated based on its own

i merits in the future. In addition Mo2(T PB)2[PMTRe(CO)3Cl]2 could be studied as a photocatalyst for CO2 CO reduction with Re acting as the catalytic center and Mo2 acting as a photosensitizing unit.

Several chapters of this dissertation describe the synthesis and characterization of model complexes to better understand polymeric materials that could eventually be made.

Chapter 5 considers the electronic properties of a theoretical mixed metal polymer.

Hybrid M2-Pt acetylide oligomers were studied using DFT and TD-DFT calculations.

The oligomers were extended up to five repeating units to represent a final polymer. As more units were added to the chain there was a decrease in the HOMO-LUMO gap in both Mo and W complexes. There was virtually no change between the 4th and 5th repeating unit and the calculated UV-Visible absorption spectra showed very little shift indicating that, optically, five repeating units is sufficient to be representative of a polymer. With the addition of more units the formation of bands was also observed. The

162

M2δ orbitals formed bands at the HOMO level while Pt containing orbitals formed bands at lower energy. These bands indicate that a hybrid M2-Pt acetylide polymer could have excellent charge transport properties. The exciting aspect of these calculations is that the material maintains all of the interesting optical properties of small molecule M2 paddlewheel complexes while benefiting from the ability of platinum to template dialkynes into polymers. The synthesis of these complexes would be straight forward if one were to start with an alkyne terminated M2 complex and cross couple them with platinum starting materials. In the future the synthesis of these polymers could lead to materials that are uniform and easily processed into a thin film which has proven to be a difficult task with M2 units in the past. The electronic properties of the final material could be tuned based on the choice of metal and the π-conjugated bridge.

Chapter 6 introduces a new kind of ligand to the cannon of M2 paddlewheels in the form of pyridyl N-oxide ligands. While iso-nicitinate ligands have been investigated before and have been shown to be quite versatile, the formally charged pyridyl N-oxide moiety had a profound effect on the electronic structure of the molecule. X-Ray analysis of

i Mo2(T PB)2(O2CC5H4-p-NO)2, showed that the oxide is non-innocent. While it does not serve to oxidize the Mo2 core it does have an affinity for the metal-metal axis, binding in such a way as to form infinite 2D sheets. This affinity for Lewis acids was further explored by reacting the compound in situ with B(C6F6)3 to form an adduct that caused a dramatic red shift in the electronic absorption spectrum. With evidence for such a strong nucleophilic ligand the discussion turned to interactions with semiconducting films such

i + - as TiO2, NiO, and ITO. Because Mo2(T PB)2(O2CC5H4N -p-O )2 exists in a trans

163 configuration it is not ideal for bonding to a surface, the cis complex cis-

+ - Mo2(DAniF)2(O2CC5H4N -p-O )2 was synthesized. The cis configuration allows for bidentate binding to the surface of the material and thus a stronger interaction. The new dye was shown to absorb to the surface of all of the materials tested thereafter. This preliminary data suggests that pyridyl N-oxide moieties could be an exciting new anchoring group for dyes in the field of DSSCs. In the future devices could be fabricated using the cis-Mo2 dye to determine if the complexes are capable of generating a current in an electrolyte solution. It should also be noted that the 2D configuration of

i + - Mo2(T PB)2(O2CC5H4N -p-O )2 in the solid state could have interesting charge transport properties, which could be investigated further.

The idea of crystal engineering that was presented with the 2D sheets found in Chapter 6 is continued in Chapter 7. The synthesis, characterization, and structural analysis of two families of halobenzoate containing Mo2 paddlewheels was investigated with the halogens spanning from F to I. The optical properties of the homoleptic and bis-bis complexes showed a red shift in the MLCT upon descent down the periodic table. The effect the halogen has on the excited state properties is to be described in a future work.

The crystal structures of the complexes were particularly interesting as the homoleptic chloride and bis-bis bromide and iodide exhibit halogen-halogen interactions. Both types of halogen-halogen interactions are shown in this chapter as the homoleptic chloride exhibits type 2 bonding while the bromo and iodo complexes show type 1. While the fluoride derivatives were crystallized in both cases, the homoleptic fluoro complex showed no intermolecular interactions while the bis-bis fluoro complex preferred a π

164 stacking orientation over a halogen-halogen interaction. These molecules show that halogens can be used to tune not only the spectral properties of M2 units but they can also be used to influence their intermolecular interactions in the solid state. This could be a useful property to exploit when fabricating photovoltaic devices in the future.

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APPENDIX A: SUPPORTING INFORMATION FOR CHAPTER 3

Table A. 1. Select bond lengths (Å) and angles (o) for 1.

Cr(6)-C(22) 1.833(12) Cr(6)-C(23) 1.847(12) Cr(6)-C(24) 1.849(14) Mo(3)-Mo(3)#4 2.0974(16) Mo(3)-O(3) 2.102(6) Mo(3)-O(1) 2.105(6) Mo(3)-O(4) 2.113(6) Mo(3)-O(2) 2.114(6)

Mo(3)#4-Mo(3)-O(3) 92.19(17) Mo(3)#4-Mo(3)-O(1) 91.69(18) O(3)-Mo(3)-O(1) 176.1(2) Mo(3)#4-Mo(3)-O(4) 91.73(18) O(3)-Mo(3)-O(4) 88.0(2) O(1)-Mo(3)-O(4) 91.5(2) Mo(3)#4-Mo(3)-O(2) 91.83(17) O(3)-Mo(3)-O(2) 91.7(2) O(1)-Mo(3)-O(2) 88.6(2) O(4)-Mo(3)-O(2) 176.4(2) C(15)-O(1)-Mo(3) 117.1(6) C(1)-O(2)-Mo(3) 115.9(6) C(22)-Cr(6)-C(23) 85.3(5) C(22)-Cr(6)-C(24) 89.2(5) C(23)-Cr(6)-C(24) 91.0(6)

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Table A. 2. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for 1. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

______

x y z U(eq)

______

C(79) 8270(6) 6792(6) 9131(6) 49(3) C(81) 9250(10) 2907(9) 3903(10) 94(5) C(82) 9226(12) 2712(10) 4637(12) 104(6) C(83) 9927(15) 2331(9) 5051(9) 104(6) C(84) 10658(10) 2175(8) 4656(9) 81(4) C(85) 10683(9) 2371(8) 3918(9) 77(4) C(86) 9980(10) 2731(9) 3553(9) 88(4) C(87) 8375(9) 3959(7) 1372(10) 80(4) C(88) 8926(10) 4005(8) 757(8) 79(4) C(89) 9493(8) 3389(8) 833(7) 69(3) C(90) 9502(8) 2721(8) 1497(8) 71(4) C(91) 8965(8) 2675(7) 2113(7) 64(3) C(92) 8397(9) 3295(8) 2037(9) 82(4) C(93) 3071(11) 6270(9) 5937(8) 94(5) C(94) 2770(10) 5743(9) 5801(8) 93(4) C(95) 2600(9) 5000(9) 6384(11) 104(5) C(96) 2787(12) 4822(12) 7089(12) 131(7) C(97) 3089(16) 5370(13) 7206(11) 146(8) C(98) 3225(12) 6062(11) 6642(10) 115(5) C(1B) 7082(11) 706(10) 593(12) 109(5) C(2B) 7283(11) -49(11) 1064(9) 99(5) C(3B) 7468(11) -555(9) 784(11) 104(5) C(4B) 7414(12) -369(12) 88(12) 114(6) C(5B) 7193(13) 415(14) -387(10) 123(6) C(6B) 7032(9) 960(8) -144(9) 115(6) C(7A) 9567(9) 2649(8) 7807(9) 201(14) C(8A) 9073(11) 2057(11) 8133(10) 119(6) C(9A) 9278(11) 1462(10) 7968(10) 112(6) C(10A) 9931(13) 1462(12) 7506(13) 141(8) C(11A) 10404(19) 2062(18) 7175(17) 243(19) C(12A) 10270(20) 2661(16) 7354(16) 280(20) C(1C) 427(11) 5323(11) 5305(10) 102(5) C(2C) 610(15) 4600(12) 5423(14) 157(10) C(3C) -143(13) 5736(11) 4860(15) 153(10) C(25) 3975(6) 4883(5) 4119(5) 33(2) C(26) 3427(6) 4814(5) 3627(5) 33(2) Continued on next page

167

Table A.2 Continued C(27) 3791(7) 4621(5) 3038(5) 39(2) C(28) 3258(7) 4448(6) 2656(5) 43(3) C(29) 2393(7) 4449(6) 2844(6) 48(3) C(30) 2029(6) 4666(6) 3387(6) 50(3) C(31) 2550(6) 4845(5) 3799(5) 41(2) C(32) 4922(6) 6563(5) 4010(5) 31(2) C(33) 4799(6) 7407(5) 3420(5) 32(2) C(34) 4023(6) 7663(5) 3095(5) 36(2) C(35) 3916(6) 8440(5) 2546(5) 37(2) C(36) 4528(6) 8970(5) 2308(5) 37(2) C(37) 5281(6) 8693(5) 2641(5) 37(2) C(38) 5433(6) 7916(5) 3198(5) 32(2) C(39) 6519(7) 8278(6) 3734(7) 62(3) C(40) 6275(6) 7670(6) 3543(5) 40(2) C(41) 6951(7) 7482(7) 3024(6) 63(3) C(42) 3320(6) 7116(6) 3302(5) 40(2) C(43) 3068(7) 7104(7) 2619(6) 60(3) C(44) 2568(7) 7335(7) 3734(7) 67(3) C(45) 4663(9) 10422(6) 1866(7) 67(3) C(46) 4396(7) 9805(5) 1687(5) 46(3) C(47) 4838(8) 9890(7) 938(6) 64(3) C(48) 2341(7) 3254(7) 4785(6) 50(3) C(49) 2882(7) 2791(7) 3784(6) 52(3) C(50) 3973(7) 3179(6) 4357(6) 45(3) C(54) 4940(5) 4031(6) 9379(5) 33(2) C(55) 4911(6) 3495(5) 9046(5) 35(2) C(56) 5073(6) 2676(6) 9466(6) 41(2) C(57) 4992(6) 2171(6) 9152(6) 47(3) C(58) 4741(6) 2491(6) 8426(5) 40(2) C(59) 4589(6) 3310(6) 8000(5) 37(2) C(60) 4685(6) 3816(6) 8295(5) 34(2) C(61) 3406(7) 2202(7) 10027(7) 56(3) C(62) 2903(7) 2753(6) 8744(6) 49(3) C(63) 3139(7) 3722(7) 9211(5) 44(2) C(64) 6665(6) 5046(6) 9472(5) 36(2) C(65) 7555(5) 5014(5) 9159(5) 31(2) C(66) 7916(6) 4320(6) 9120(5) 35(2) C(67) 8752(6) 4324(6) 8789(5) 42(2) C(68) 9231(6) 4960(6) 8526(5) 37(2) C(69) 8854(6) 5624(6) 8576(5) 41(2) C(70) 8021(6) 5673(5) 8880(5) 33(2) C(71) 7644(6) 6431(5) 8893(6) 40(2) C(72) 7349(7) 7020(6) 8129(6) 54(3) C(73) 10120(6) 4937(6) 8169(6) 45(3) Continued on next page 168

Table A.2 Continued C(74) 7438(6) 3589(6) 9400(6) 42(2) C(75) 7868(9) 2866(7) 10001(8) 80(4) C(76) 7306(8) 3431(8) 8748(7) 71(4) C(77) 10146(7) 4942(8) 7418(7) 70(4) C(78) 10684(7) 4261(8) 8678(7) 74(4) Cr(4) 3805(1) 2923(1) 9094(1) 39(1) Cr(5) 3003(1) 3681(1) 3881(1) 41(1) Mo(1) 5147(1) 4513(1) 10511(1) 29(1) Mo(2) 5526(1) 4906(1) 4670(1) 28(1) O(5) 4782(4) 4822(3) 3954(3) 31(1) O(6) 5515(4) 6119(3) 3901(3) 32(1) O(7) 3645(4) 5011(3) 4662(3) 32(1) O(8) 5585(4) 3680(3) 5392(3) 30(1) O(9) 6444(4) 4542(4) 10150(3) 34(1) O(10) 4787(4) 4767(4) 8979(3) 33(1) O(11) 6134(4) 5562(3) 9057(3) 33(1) O(12) 5104(4) 3720(3) 10073(3) 34(1) O(16) 2825(5) 2227(5) 3732(5) 64(2) O(17) 1907(5) 3005(5) 5339(5) 73(2) O(18) 3165(6) 1710(5) 10620(5) 82(3) O(19) 2319(5) 2645(6) 8541(5) 76(3) O(20) 2733(5) 4245(5) 9253(4) 61(2) O(21) 4587(5) 2901(4) 4648(5) 60(2) Mo(3) 9931(1) 9403(1) 5178(1) 33(1) O(1) 8616(4) 9564(4) 5387(4) 38(2) O(2) 10037(4) 9108(4) 6311(4) 39(2) O(3) 11233(4) 9163(4) 4986(3) 35(2) O(4) 9822(4) 9623(4) 4067(4) 39(2) O(13) 6170(5) 9879(5) 4075(5) 70(2) O(14) 4608(5) 11548(5) 4328(6) 79(3) O(15) 7196(7) 12014(6) 3493(5) 91(3) Cr(6) 6298(1) 10812(1) 4888(1) 42(1) C(1) 10101(6) 9689(6) 6441(6) 39(2) C(2) 10066(6) 9505(6) 7255(6) 44(3) C(3) 10799(6) 9393(6) 7589(6) 46(3) C(4) 10718(7) 9219(7) 8359(6) 58(3) C(5) 9937(8) 9163(7) 8763(6) 59(3) C(6) 9249(7) 9285(6) 8389(6) 50(3) C(7) 9282(6) 9467(6) 7656(6) 43(2) C(8) 8470(6) 9637(6) 7261(6) 49(3) C(9) 7852(10) 10198(11) 7424(9) 115(7) C(10) 8107(9) 8868(8) 7483(8) 89(5) C(11) 11654(6) 9513(7) 7125(6) 52(3) C(12) 12377(7) 8976(8) 7571(7) 69(4) C(13) 11846(8) 10373(8) 6764(7) 68(3) Continued on next page 169

Table A.2 Continued C(14) 9852(9) 8953(10) 9609(7) 82(4) C(15) 8310(6) 10249(6) 5286(6) 38(2) C(16) 7086(6) 11089(6) 5511(6) 42(2) C(17) 7412(6) 10373(6) 5535(6) 41(2) C(18) 6872(6) 9751(6) 5793(5) 43(2) C(19) 6018(6) 9876(7) 6042(5) 49(3) C(20) 5725(6) 10593(7) 6005(6) 50(3) C(21) 6240(6) 11204(7) 5755(6) 47(3) C(22) 6239(6) 10232(7) 4396(6) 48(3) C(23) 5265(8) 11283(6) 4543(7) 58(3) C(24) 6851(9) 11551(8) 4023(7) 66(3) C(80) 9572(10) 8134(9) 10070(7) 93(5) C(99) 10575(11) 9143(13) 9839(9) 125(7) C(1A) 4774(7) 2608(9) 2546(7) 147(7) C(2A) 5007(8) 2133(7) 2194(8) 145(8) C(3A) 5746(8) 2245(6) 1714(7) 110(5) C(4A) 6252(7) 2833(7) 1586(6) 97(4) C(5A) 6018(8) 3308(6) 1939(7) 157(9) C(6A) 5279(9) 3195(8) 2419(7) 150(8)

170

Figure A. 2. fs-TA spectra of 2 in THF, λex = 675 nm, (inset) kinetic decay at 495 nm.

171

APPENDIX B: SUPPORTING INFORMATION FOR CHAPTER 4

Table B. 1. Select bond lengths (Å) and angles (o) for HL.

Re(1)-C(12) 1.908(6)

Re(1)-C(11) 1.923(6) Re(1)-C(13) 1.941(6) Re(1)-N(2) 2.184(4) Re(1)-N(1) 2.202(4) Re(1)-Cl(3) 2.4798(14)

C(12)-Re(1)-C(11) 89.4(2) C(12)-Re(1)-C(13) 91.0(2) C(11)-Re(1)-C(13) 86.9(2) C(12)-Re(1)-N(2) 95.9(2) C(11)-Re(1)-N(2) 95.9(2) C(13)-Re(1)-N(2) 172.6(2) C(12)-Re(1)-N(1) 91.2(2) C(11)-Re(1)-N(1) 170.8(2) C(13)-Re(1)-N(1) 102.34(19) N(2)-Re(1)-N(1) 74.91(15) C(12)-Re(1)-Cl(3) 175.29(17) C(11)-Re(1)-Cl(3) 94.79(19) C(13)-Re(1)-Cl(3) 91.30(18) N(2)-Re(1)-Cl(3) 81.64(13) N(1)-Re(1)-Cl(3) 84.30(12)

172

Table B. 2. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for HL. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

______

x y z U(eq)

______

Re(1) 3108(1) 797(1) 7616(1) 24(1) S(1) 2531(1) 2102(2) 10094(1) 28(1) Cl(3) 3561(1) -1673(2) 8232(1) 32(1) C(1) 137(5) 1901(7) 10022(3) 28(1) O(4) -837(3) 1541(5) 9749(2) 37(1) N(1) 2342(3) 1288(5) 8676(2) 22(1) N(2) 4574(4) 1476(5) 8470(2) 25(1) C(12) 2740(5) 2757(7) 7224(3) 31(1) O(1) 4546(4) 278(6) 6284(2) 45(1) O(5) 431(3) 2484(5) 10715(2) 39(1) O(3) 1050(4) -563(5) 6538(3) 43(1) O(2) 2519(4) 3933(5) 6992(3) 44(1) C(2) 1164(4) 1722(6) 9608(3) 26(1) C(3) 1210(4) 1299(7) 8860(3) 25(1) C(7) 5218(5) 2022(6) 9813(3) 30(1) C(4) 222(5) 873(7) 8266(4) 34(2) C(6) 4343(4) 1753(6) 9203(3) 24(1) C(5) 3109(4) 1681(6) 9279(3) 25(1) C(8) 6363(5) 2006(7) 9674(3) 34(1) C(13) 1796(5) -36(7) 6938(3) 32(1) C(9) 6599(4) 1737(7) 8936(3) 30(1) C(10) 5692(5) 1487(7) 8350(3) 28(1) C(11) 4010(5) 466(7) 6785(3) 31(1) O(6) 1302(4) 6808(5) 8568(3) 41(1) C(15) 1775(7) 5399(8) 8813(5) 60(2)

173

Table B. 3. Select bond lengths (Å) and angles (o) for 3.

Mo(1)-O(2)#1 2.1039(14) Mo(1)-Mo(1)#1 2.1051(3) Mo(1)-O(1) 2.1059(14) Mo(1)-O(4) 2.1102(14) Mo(1)-O(3) 2.1133(14) O(2)-Mo(1)#1 2.1039(14)

O(2)#1-Mo(1)-Mo(1)#1 91.68(4) O(2)#1-Mo(1)-O(1) 176.61(5) Mo(1)#1-Mo(1)-O(1) 91.71(4) O(2)#1-Mo(1)-O(4) 89.58(6) Mo(1)#1-Mo(1)-O(4) 90.90(4) O(1)-Mo(1)-O(4) 90.36(6) O(2)#1-Mo(1)-O(3) 90.10(6) Mo(1)#1-Mo(1)-O(3) 92.53(4) O(1)-Mo(1)-O(3) 89.75(6) O(4)-Mo(1)-O(3) 176.56(5) C(1)-O(1)-Mo(1) 117.35(13) C(1)-O(2)-Mo(1)#1 117.47(13) C(12)-O(3)-Mo(1) 116.21(14) C(12)#1-O(4)-Mo(1) 118.01(13)

174

Table B. 4. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for HL. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

______

x y z U(eq)

______

C(1) 1032(2) 56(2) 2918(2) 37(1) C(12) -840(2) 1964(2) 4191(2) 40(1) C(13) -1256(2) 3054(2) 3723(2) 47(1) C(14) -1806(3) 3597(2) 4409(3) 61(1) C(15) -2119(4) 4638(3) 3925(4) 85(1) C(16) -1913(4) 5133(2) 2822(4) 91(1) C(17) -1379(4) 4566(2) 2174(3) 82(1) C(18) -1037(3) 3525(2) 2603(2) 59(1) C(19) -400(4) 2918(3) 1867(2) 73(1) C(20) 1139(4) 3261(3) 1296(3) 96(1) C(21) -1028(5) 3053(3) 1029(3) 102(1) C(22) -2034(4) 3064(3) 5628(3) 75(1) C(23) -848(5) 3430(4) 5830(4) 110(2) C(24) -3385(4) 3229(4) 6394(4) 109(1) C(28) -3056(4) -2413(3) 5131(3) 80(1) C(29) -4298(6) -3210(4) 5760(5) 157(3) C(30) -4964(5) -3101(4) 6835(4) 132(2) C(31) -3963(3) -2329(3) 6818(3) 82(1) Mo(1) -938(1) -407(1) 5156(1) 33(1) O(1) -196(1) -391(1) 3558(1) 37(1) O(2) 1791(1) 472(1) 3229(1) 37(1) O(3) -1658(1) 1086(1) 4550(1) 37(1) O(4) -333(2) -1949(1) 5786(1) 38(1) O(5) -3123(2) -1699(2) 5675(2) 61(1) O(1A) 3481(17) 5446(13) 980(20) 200(9) C(1A) 2375(15) 5980(14) 1300(20) 133(6) C(2A) 2820(20) 7115(13) 740(20) 127(6) C(3A) 4050(30) 7224(17) -200(20) 175(9) C(4A) 4390(30) 6210(20) -10(20) 201(11) O(1B) 4070(20) 5549(12) 1206(15) 239(8) C(1B) 2735(18) 5645(13) 1708(11) 147(5) C(2B) 2527(17) 6732(18) 1173(14) 157(6) C(3B) 3854(16) 7329(11) 297(14) 141(5) C(4B) 4656(15) 6536(15) 263(15) 172(7) C(2) 1592(2) 81(2) 1794(2) 39(1) N(1) 3437(2) 631(2) 20(2) 58(1) C(4) 1371(2) -380(2) 398(2) 49(1) C(3) 833(3) -406(2) 1437(2) 53(1) C(6) 2898(3) 598(2) 1045(2) 52(1) C(5) 2665(2) 130(2) -294(2) 42(1) N(2) 2438(3) -220(2) -1779(2) 69(1) C(7) 3270(3) 143(2) -1416(2) 46(1) Continued on next page 175

Table B.4 Continued C(8) 4609(3) 508(2) -2049(2) 56(1) C(9) 5157(3) 499(3) -3077(3) 75(1) C(11) 2991(4) -226(3) -2794(3) 78(1) C(10) 4346(4) 137(3) -3466(3) 80(1) C(25A) -2266(6) 6265(3) 2327(6) 152(3) C(26A) -3222(13) 6383(10) 1826(7) 67(3) C(27A) -1265(14) 7165(12) 1989(13) 83(4) C(25B) -2266(6) 6265(3) 2327(6) 152(3) C(26B) -1750(30) 7070(13) 2520(20) 132(8) C(27B) -3506(19) 6273(11) 2370(30) 198(12)

Figure B. 1. Kinetic traces from fs-TRIR spectra of Re(PMT-H)(CO)3Cl (HL) at (a,b) -1 -1 i -1 1948 cm and 1844 cm ; and of Mo2(T PB)2[Re(PMT)(CO)3Cl]2 (2) at (c,d) 1879 cm and 1618 cm-1.

176

Figure B. 2. Kinetic traces from fs-TRIR spectra of Re(PMT-H)(CO)3Cl (HL) at (a,b) -1 -1 i -1 1948 cm and 1844 cm ; and of Mo2(T PB)2[Re(PMT)(CO)3Cl]2 (2) at (c,d) 1879 cm and 1618 cm-1.

177

APPENDIX C: SUPPORTING INFORMATION FOR CHAPTER 5

Table C. 1. Selected orbital energy levels for Mo22Pt.

Orbital Occupancy Energy (Hart) Energy (eV) LUMO+14 173 0 -0.01318 -0.358646041 LUMO+13 172 0 -0.0163 -0.443545559 LUMO+12 171 0 -0.0164 -0.446266698 LUMO+11 170 0 -0.01864 -0.507220198 LUMO+10 169 0 -0.02829 -0.769810053 LUMO+9 168 0 -0.02844 -0.773891761 LUMO+8 167 0 -0.03095 -0.842192335 LUMO+7 166 0 -0.035 -0.95239844 LUMO+6 165 0 -0.03523 -0.958657058 LUMO+5 164 0 -0.03577 -0.973351206 LUMO+4 163 0 -0.03582 -0.974711775 LUMO+3 162 0 -0.05785 -1.574178564 LUMO+2 161 0 -0.07056 -1.920035255 LUMO+1 160 0 -0.07063 -1.921940052 LUMO 159 0 -0.07388 -2.01037705 HOMO 158 2 -0.18795 -5.114379623 HOMO-1 157 2 -0.19129 -5.205265645 HOMO-2 156 2 -0.24885 -6.771552908 HOMO-3 155 2 -0.25075 -6.823254538 HOMO-4 154 2 -0.25087 -6.826519904 HOMO-5 153 2 -0.2516 -6.846384214 HOMO-6 152 2 -0.25259 -6.873323485 Continued on next page

178

Table C.1 Continued HOMO-7 151 2 -0.25295 -6.883119583 HOMO-8 150 2 -0.25952 -7.061898376 HOMO-9 149 2 -0.25963 -7.064891628 HOMO-10 148 2 -0.26625 -7.24503099 HOMO-11 147 2 -0.28089 -7.643405652 HOMO-12 146 2 -0.286 -7.782455824 HOMO-13 145 2 -0.30768 -8.372398629 HOMO-14 144 2 -0.30777 -8.374847654 HOMO-15 143 2 -0.31541 -8.582742627 172 Alpha Frozen Core Electrons

Table C. 2. Selected orbital energy levels for Mo23Pt2.

# Orbital Occupancy Energy (Hart) Energy (eV) LUMO+30 287 0 0.002283705 0.06214277 LUMO+29 286 0 0.001527724 0.04157148 LUMO+28 285 0 -0.003636141 -0.0989444 LUMO+27 284 0 -0.003671088 -0.0998954 LUMO+26 283 0 -0.008409177 -0.2288254 LUMO+25 282 0 -0.010312404 -0.2806148 LUMO+24 281 0 -0.010501794 -0.2857683 LUMO+23 280 0 -0.010506267 -0.2858901 LUMO+22 279 0 -0.011733029 -0.319272 LUMO+21 278 0 -0.012021598 -0.3271243 LUMO+20 277 0 -0.01534336 -0.4175141 LUMO+19 276 0 -0.015346272 -0.4175933 LUMO+18 275 0 -0.016479669 -0.4484346 LUMO+17 274 0 -0.02410545 -0.6559426 LUMO+16 273 0 -0.024906134 -0.6777304 LUMO+15 272 0 -0.027415364 -0.74601 LUMO+14 271 0 -0.027430944 -0.7464339 LUMO+13 270 0 -0.028683559 -0.7805193 LUMO+12 269 0 -0.030152918 -0.8205026 Continued on next page 179

Table C.2 Continued LUMO+11 268 0 -0.030534641 -0.8308899 LUMO+10 267 0 -0.034058534 -0.9267798 LUMO+9 266 0 -0.034060324 -0.9268285 LUMO+8 265 0 -0.034780425 -0.9464235 LUMO+7 264 0 -0.034781556 -0.9464543 LUMO+6 263 0 -0.055898857 -1.5210853 LUMO+5 262 0 -0.055996746 -1.523749 LUMO+4 261 0 -0.063435954 -1.7261801 LUMO+3 260 0 -0.069184285 -1.8826001 LUMO+2 259 0 -0.06949448 -1.891041 LUMO+1 258 0 -0.069504602 -1.8913164 LUMO 257 0 -0.073870336 -2.0101141 HOMO 256 2 -0.180171827 -4.9027248 HOMO-1 255 2 -0.188447272 -5.1279111 HOMO-2 254 2 -0.189098801 -5.1456401 HOMO-3 253 2 -0.243327591 -6.6212805 HOMO-4 252 2 -0.244483957 -6.6527468 HOMO-5 251 2 -0.246525524 -6.7083007 HOMO-6 250 2 -0.247829952 -6.743796 HOMO-7 249 2 -0.247889147 -6.7454068 HOMO-8 248 2 -0.249668747 -6.7938321 HOMO-9 247 2 -0.249669977 -6.7938656 HOMO-10 246 2 -0.250720965 -6.8224645 HOMO-11 245 2 -0.251614296 -6.8467732 HOMO-12 244 2 -0.251775435 -6.851158 HOMO-13 243 2 -0.253580961 -6.9002889 HOMO-14 242 2 -0.258539559 -7.0352192 HOMO-15 241 2 -0.258540717 -7.0352507 HOMO-16 240 2 -0.262332548 -7.1384317 HOMO-17 239 2 -0.265566982 -7.2264451 HOMO-18 238 2 -0.27879419 -7.5863758 HOMO-19 237 2 -0.278813027 -7.5868883 HOMO-20 236 2 -0.28255124 -7.6886103 HOMO-21 235 2 -0.284452638 -7.74035 HOMO-22 234 2 -0.300485046 -8.176614 Continued on next page 180

Table C.2 Continued HOMO-23 233 2 -0.306576304 -8.3423655 HOMO-24 232 2 -0.306577568 -8.3423999 HOMO-25 231 2 -0.309889935 -8.432534 HOMO-26 230 2 -0.310332232 -8.4445695 HOMO-27 229 2 -0.314713755 -8.5637968 HOMO-28 228 2 -0.314857012 -8.5676951 HOMO-29 227 2 -0.3157335 -8.5915455 HOMO-30 226 2 -0.315734606 -8.5915756 # 288 Alpha Frozen Core Electrons

Table C. 3. Selected orbital energy levels for Mo24Pt3.

# Orbital Occupancy Energy (hart) Energy (eV) LUMO+40 395 0 0.002015215 0.05483679 LUMO+39 394 0 -0.003415643 -0.0929444 LUMO+38 393 0 -0.003420249 -0.0930697 LUMO+37 392 0 -0.006795244 -0.184908 LUMO+36 391 0 -0.008030779 -0.2185286 LUMO+35 390 0 -0.009011358 -0.2452115 LUMO+34 389 0 -0.009298911 -0.2530362 LUMO+33 388 0 -0.00981079 -0.2669652 LUMO+32 387 0 -0.009882055 -0.2689044 LUMO+31 386 0 -0.010497004 -0.285638 LUMO+30 385 0 -0.011278292 -0.3068979 LUMO+29 384 0 -0.011456054 -0.3117351 LUMO+28 383 0 -0.011501519 -0.3129722 LUMO+27 382 0 -0.015120066 -0.4114379 LUMO+26 381 0 -0.015120427 -0.4114477 LUMO+25 380 0 -0.015542565 -0.4229347 LUMO+24 379 0 -0.021297323 -0.5795296 LUMO+23 378 0 -0.023183058 -0.6308431 LUMO+22 377 0 -0.023429429 -0.6375472 LUMO+21 376 0 -0.02717049 -0.7393466 LUMO+20 375 0 -0.027192231 -0.7399382 LUMO+19 374 0 -0.027197347 -0.7400775 LUMO+18 373 0 -0.027683094 -0.7532953 Continued on next page 181

Table C.3 Continued LUMO+17 372 0 -0.027877265 -0.758579 LUMO+16 371 0 -0.029270232 -0.7964835 LUMO+15 370 0 -0.029270516 -0.7964913 LUMO+14 369 0 -0.030041947 -0.817483 LUMO+13 368 0 -0.033820135 -0.9202927 LUMO+12 367 0 -0.033820293 -0.920297 LUMO+11 366 0 -0.034545322 -0.940026 LUMO+10 365 0 -0.034545516 -0.9400313 LUMO+9 364 0 -0.054031707 -1.4702775 LUMO+8 363 0 -0.055549211 -1.5115709 LUMO+7 362 0 -0.055552617 -1.5116636 LUMO+6 361 0 -0.062537358 -1.7017281 LUMO+5 360 0 -0.062538186 -1.7017506 LUMO+4 359 0 -0.066533527 -1.8104693 LUMO+3 358 0 -0.069254967 -1.8845235 LUMO+2 357 0 -0.069256473 -1.8845645 LUMO+1 356 0 -0.071162252 -1.9364234 LUMO 355 0 -0.07352518 -2.0007219 HOMO 354 2 -0.178070871 -4.8455548 HOMO-1 353 2 -0.181028818 -4.9260447 HOMO-2 352 2 -0.188462277 -5.1283194 HOMO-3 351 2 -0.188577655 -5.131459 HOMO-4 350 2 -0.242165414 -6.5896561 HOMO-5 349 2 -0.242419057 -6.596558 HOMO-6 348 2 -0.242425196 -6.5967251 HOMO-7 347 2 -0.244632337 -6.6567845 HOMO-8 346 2 -0.245462011 -6.679361 HOMO-9 345 2 -0.245953111 -6.6927245 HOMO-10 344 2 -0.246408911 -6.7051275 HOMO-11 343 2 -0.247204855 -6.7267862 HOMO-12 342 2 -0.248751542 -6.7688737 HOMO-13 341 2 -0.249429565 -6.7873237 HOMO-14 340 2 -0.249429777 -6.7873294 HOMO-15 339 2 -0.250154584 -6.8070524 HOMO-16 338 2 -0.251404878 -6.8410747 HOMO-17 337 2 -0.251452159 -6.8423613 HOMO-18 336 2 -0.252686975 -6.8759623 HOMO-19 335 2 -0.25270549 -6.8764661 Continued on next page

182

Table C.3 Continued HOMO-20 334 2 -0.258304211 -7.0288151 HOMO-21 333 2 -0.258304217 -7.0288152 HOMO-22 332 2 -0.259940569 -7.0733426 HOMO-23 331 2 -0.263573117 -7.1721893 HOMO-24 330 2 -0.264971308 -7.210236 HOMO-25 329 2 -0.276688526 -7.5290777 HOMO-26 328 2 -0.278382579 -7.5751753 HOMO-27 327 2 -0.27838352 -7.5752009 HOMO-28 326 2 -0.280169285 -7.623794 HOMO-29 325 2 -0.283066909 -7.7026424 HOMO-30 324 2 -0.283680225 -7.7193315 HOMO-31 323 2 -0.29958207 -8.1520427 HOMO-32 322 2 -0.299584964 -8.1521215 HOMO-33 321 2 -0.306332258 -8.3357247 HOMO-34 320 2 -0.306334528 -8.3357865 HOMO-35 319 2 -0.308886353 -8.4052252 HOMO-36 318 2 -0.309004659 -8.4084444 HOMO-37 317 2 -0.309004822 -8.4084489 HOMO-38 316 2 -0.309913201 -8.4331671 HOMO-39 315 2 -0.314501783 -8.5580288 HOMO-40 314 2 -0.31451103 -8.5582804 404 Core # Alpha Frozen Electrons

Table C. 4. Selected orbital energy levels for Mo25Pt4.

# Orbital Occupancy Energy(hart) Energy (eV) Symmetry LUMO+50 503 0 -0.00333 -0.090613909 (bg) LUMO+49 502 0 -0.00333 -0.090613909 (au) LUMO+48 501 0 -0.00595 -0.161907735 (ag) LUMO+47 500 0 -0.00701 -0.190751802 (bg) LUMO+46 499 0 -0.00759 -0.206534405 (bu) LUMO+45 498 0 -0.0087 -0.236739041 (bu) LUMO+44 497 0 -0.00897 -0.244086114 (au) LUMO+43 496 0 -0.00922 -0.25088896 (ag) Continued on next page

183

Table C.4 Continued LUMO+42 495 0 -0.00946 -0.257419693 (ag) LUMO+41 494 0 -0.00955 -0.259868717 (bu) LUMO+40 493 0 -0.00964 -0.262317742 (bu) LUMO+39 492 0 -0.01018 -0.277011889 (bu) LUMO+38 491 0 -0.01029 -0.280005141 (ag) LUMO+37 490 0 -0.01137 -0.309393436 (bu) LUMO+36 489 0 -0.01138 -0.30966555 (ag) LUMO+35 488 0 -0.01174 -0.319461648 (bg) LUMO+34 487 0 -0.01467 -0.399191003 (bu) LUMO+33 486 0 -0.01467 -0.399191003 (ag) LUMO+32 485 0 -0.01503 -0.408987102 (au) LUMO+31 484 0 -0.01936 -0.526812394 (bg) LUMO+30 483 0 -0.02242 -0.610079229 (bu) LUMO+29 482 0 -0.02314 -0.629671426 (ag) LUMO+28 481 0 -0.0232 -0.631304109 (bu) LUMO+27 480 0 -0.02394 -0.651440533 (au) LUMO+26 479 0 -0.02678 -0.728720864 (ag) LUMO+25 478 0 -0.02711 -0.73770062 (bu) LUMO+24 477 0 -0.02712 -0.737972734 (ag) LUMO+23 476 0 -0.02765 -0.752394768 (bu) LUMO+22 475 0 -0.02766 -0.752666881 (ag) LUMO+21 474 0 -0.02819 -0.767088915 (bg) LUMO+20 473 0 -0.02828 -0.76953794 (bg) LUMO+19 472 0 -0.0291 -0.791851274 (au) LUMO+18 471 0 -0.0291 -0.791851274 (bg) LUMO+17 470 0 -0.02975 -0.809538674 (au) LUMO+16 469 0 -0.03369 -0.916751527 (ag) LUMO+15 468 0 -0.03369 -0.916751527 (bu) LUMO+14 467 0 -0.03449 -0.938520634 (bg) Continued on next page

184

Table C.4 Continued LUMO+13 466 0 -0.03449 -0.938520634 (au) LUMO+12 465 0 -0.0536 -1.458530182 (bu) LUMO+11 464 0 -0.0537 -1.461251321 (ag) LUMO+10 463 0 -0.05548 -1.509687584 (bu) LUMO+9 462 0 -0.05548 -1.509687584 (ag) LUMO+8 461 0 -0.0616 -1.676221254 (au) LUMO+7 460 0 -0.06234 -1.696357679 (bg) LUMO+6 459 0 -0.06235 -1.696629792 (au) LUMO+5 458 0 -0.06518 -1.773638009 (bg) LUMO+4 457 0 -0.06873 -1.870238422 (au) LUMO+3 456 0 -0.06924 -1.884116228 (bg) LUMO+2 455 0 -0.06924 -1.884116228 (au) LUMO+1 454 0 -0.07203 -1.96003599 (bg) LUMO 453 0 -0.0733 -1.994594447 (au) HOMO 452 2 -0.17703 -4.81723131 (bg) HOMO-1 451 2 -0.17937 -4.880905948 (au) HOMO-2 450 2 -0.1813 -4.933423919 (bg) HOMO-3 449 2 -0.18845 -5.127985315 (au) HOMO-4 448 2 -0.18847 -5.128529542 (bg) HOMO-5 447 2 -0.24109 -6.560392569 (ag) HOMO-6 446 2 -0.24164 -6.57535883 (bu) HOMO-7 445 2 -0.24221 -6.590869319 (bu) HOMO-8 444 2 -0.24221 -6.590869319 (ag) HOMO-9 443 2 -0.24328 -6.6199855 (bu) HOMO-10 442 2 -0.2435 -6.625972004 (au) HOMO-11 441 2 -0.24535 -6.676313064 (au) HOMO-12 440 2 -0.24538 -6.677129406 (bg) HOMO-13 439 2 -0.24589 -6.691007212 (au) HOMO-14 438 2 -0.24597 -6.693184122 (ag) Continued on next page

185

Table C.4 Continued HOMO-15 437 2 -0.24676 -6.714681116 (bg) HOMO-16 436 2 -0.24689 -6.718218596 (bu) HOMO-17 435 2 -0.24921 -6.781349007 (au) HOMO-18 434 2 -0.24942 -6.787063397 (ag) HOMO-19 433 2 -0.24942 -6.787063397 (bu) HOMO-20 432 2 -0.24987 -6.79930852 (bg) HOMO-21 431 2 -0.25159 -6.846112101 (au) HOMO-22 430 2 -0.2516 -6.846384214 (bg) HOMO-23 429 2 -0.25181 -6.852098605 (ag) HOMO-24 428 2 -0.2525 -6.87087446 (bu) HOMO-25 427 2 -0.2525 -6.87087446 (ag) HOMO-26 426 2 -0.25828 -7.02815626 (ag) HOMO-27 425 2 -0.25828 -7.02815626 (bu) HOMO-28 424 2 -0.25867 -7.038768699 (ag) HOMO-29 423 2 -0.26149 -7.115504802 (bu) HOMO-30 422 2 -0.26404 -7.184893831 (ag) HOMO-31 421 2 -0.26467 -7.202037003 (bu) HOMO-32 420 2 -0.27629 -7.518233285 (bu) HOMO-33 419 2 -0.27631 -7.518777513 (ag) HOMO-34 418 2 -0.27832 -7.573472395 (bu) HOMO-35 417 2 -0.27832 -7.573472395 (ag) HOMO-36 416 2 -0.2791 -7.594697274 (au) HOMO-37 415 2 -0.28092 -7.644221993 (bg) HOMO-38 414 2 -0.28322 -7.706808176 (au) HOMO-39 413 2 -0.2834 -7.711706226 (bg) HOMO-40 412 2 -0.29871 -8.128312515 (au) HOMO-41 411 2 -0.29937 -8.146272028 (au) HOMO-42 410 2 -0.29937 -8.146272028 (bg) HOMO-43 409 2 -0.30635 -8.336207488 (au) Continued on next page

186

Table C.4 Continued HOMO-44 408 2 -0.30635 -8.336207488 (bg) HOMO-45 407 2 -0.30804 -8.382194727 (ag) HOMO-46 406 2 -0.30816 -8.385460093 (bg) HOMO-47 405 2 -0.30879 -8.402603265 (au) HOMO-48 404 2 -0.30879 -8.402603265 (bg) HOMO-49 403 2 -0.3092 -8.413759933 (bu) HOMO-50 402 2 -0.30966 -8.426277169 (ag) 520 # Alpha Frozen Core Electrons

Table C. 5. Selected orbital energy levels for W22Pt.

Orbital Occupancy Energy (Hart) Energy (eV) LUMO+14 173 0 -0.01192 -0.324359697 LUMO+13 172 0 -0.01505 -0.409531329 LUMO+12 171 0 -0.01553 -0.422592794 LUMO+11 170 0 -0.01633 -0.444361901 LUMO+10 169 0 -0.01634 -0.444634015 LUMO+9 168 0 -0.01893 -0.515111499 LUMO+8 167 0 -0.01985 -0.540145972 LUMO+7 166 0 -0.01988 -0.540962314 LUMO+6 165 0 -0.03254 -0.885458435 LUMO+5 164 0 -0.03478 -0.946411936 LUMO+4 163 0 -0.03484 -0.948044619 LUMO+3 162 0 -0.04139 -1.126279184 LUMO+2 161 0 -0.0414 -1.126551298 LUMO+1 160 0 -0.05566 -1.514585633 LUMO 159 0 -0.0725 -1.97282534 HOMO 158 2 -0.16833 -4.580492269 HOMO-1 157 2 -0.17233 -4.689337805 HOMO-2 156 2 -0.22362 -6.08500969 HOMO-3 155 2 -0.22362 -6.08500969 HOMO-4 154 2 -0.2259 -6.147051646 HOMO-5 153 2 -0.22592 -6.147595873 HOMO-6 152 2 -0.24696 -6.720123393 HOMO-7 151 2 -0.24975 -6.796043154 Continued on next page 187

Table C.5 Continued HOMO-8 150 2 -0.26016 -7.079313661 HOMO-9 149 2 -0.26016 -7.079313661 HOMO-10 148 2 -0.26461 -7.20040432 HOMO-11 147 2 -0.27821 -7.570479143 HOMO-12 146 2 -0.2839 -7.725311918 HOMO-13 145 2 -0.30956 -8.423556031 HOMO-14 144 2 -0.30956 -8.423556031 HOMO-15 143 2 -0.31614 -8.602606938 300 Core # Alpha Frozen Electrons

Table C. 6. Selected orbital energy levels for W23Pt2.

# Orbital Occupancy Energy (Hart) Energy (eV) LUMO+30 287 0 0.001604621 0.04366395 LUMO+29 286 0 0.000702317 0.01911103 LUMO+28 285 0 -0.006003167 -0.1633545 LUMO+27 284 0 -0.006135648 -0.1669595 LUMO+26 283 0 -0.006183087 -0.1682504 LUMO+25 282 0 -0.008640151 -0.2351105 LUMO+24 281 0 -0.009947721 -0.2706912 LUMO+23 280 0 -0.01016432 -0.2765852 LUMO+22 279 0 -0.010443281 -0.2841761 LUMO+21 278 0 -0.010719976 -0.2917054 LUMO+20 277 0 -0.011862311 -0.3227899 LUMO+19 276 0 -0.01431345 -0.3894888 LUMO+18 275 0 -0.014337911 -0.3901544 LUMO+17 274 0 -0.015201086 -0.4136426 LUMO+16 273 0 -0.015401591 -0.4190986 LUMO+15 272 0 -0.015402702 -0.4191288 LUMO+14 271 0 -0.016839631 -0.4582297 LUMO+13 270 0 -0.019003673 -0.5171163 LUMO+12 269 0 -0.019004369 -0.5171352 LUMO+11 268 0 -0.025636285 -0.6975988 LUMO+10 267 0 -0.030888246 -0.8405119 LUMO+9 266 0 -0.032352461 -0.8803552 LUMO+8 265 0 -0.033981221 -0.9246761 Continued on next page

188

Table C.6 Continued LUMO+7 264 0 -0.033982549 -0.9247122 LUMO+6 263 0 -0.034926834 -0.9504075 LUMO+5 262 0 -0.040446654 -1.1006094 LUMO+4 261 0 -0.040447236 -1.1006253 LUMO+3 260 0 -0.053871408 -1.4659156 LUMO+2 259 0 -0.053945641 -1.4679356 LUMO+1 258 0 -0.066919707 -1.8209778 LUMO 257 0 -0.073559383 -2.0016526 HOMO 256 2 -0.16159017 -4.3970922 HOMO-1 255 2 -0.169340661 -4.6079938 HOMO-2 254 2 -0.170281474 -4.6335946 HOMO-3 253 2 -0.216765918 -5.8985006 HOMO-4 252 2 -0.221349291 -6.0232206 HOMO-5 251 2 -0.222671726 -6.0592058 HOMO-6 250 2 -0.222672006 -6.0592135 HOMO-7 249 2 -0.224999718 -6.1225537 HOMO-8 248 2 -0.225001271 -6.122596 HOMO-9 247 2 -0.242813336 -6.6072869 HOMO-10 246 2 -0.245633956 -6.6840399 HOMO-11 245 2 -0.246044271 -6.6952051 HOMO-12 244 2 -0.248760535 -6.7691184 HOMO-13 243 2 -0.255221656 -6.9449345 HOMO-14 242 2 -0.259226619 -7.0539151 HOMO-15 241 2 -0.259226836 -7.053921 HOMO-16 240 2 -0.260857369 -7.09829 HOMO-17 239 2 -0.2639574 -7.1826462 HOMO-18 238 2 -0.276287398 -7.5181625 HOMO-19 237 2 -0.276303127 -7.5185905 HOMO-20 236 2 -0.280555236 -7.6342963 HOMO-21 235 2 -0.282451124 -7.685886 HOMO-22 234 2 -0.302831909 -8.2404754 HOMO-23 233 2 -0.308581918 -8.3969411 HOMO-24 232 2 -0.308582092 -8.3969458 HOMO-25 231 2 -0.31296304 -8.5161575 HOMO-26 230 2 -0.313595706 -8.5333732 HOMO-27 229 2 -0.31426193 -8.5515021 HOMO-28 228 2 -0.314263333 -8.5515402 HOMO-29 227 2 -0.317601428 -8.6423744 Continued on next page 189

Table C.6 Continued HOMO-30 226 2 -0.31770317 -8.645143 480 # Alpha Frozen Core Electrons

Table C. 7. Selected orbital energy levels for W24Pt3.

# Orbital Occupancy Energy (hart) Energy (eV) LUMO+30 385 0 -0.010012872 -0.2724641 LUMO+29 384 0 -0.010161593 -0.276511 LUMO+28 383 0 -0.011068357 -0.3011853 LUMO+27 382 0 -0.011075404 -0.3013771 LUMO+26 381 0 -0.011224888 -0.3054447 LUMO+25 380 0 -0.01409221 -0.3834685 LUMO+24 379 0 -0.014094105 -0.3835201 LUMO+23 378 0 -0.014432584 -0.3927306 LUMO+22 377 0 -0.01448738 -0.3942217 LUMO+21 376 0 -0.015178304 -0.4130227 LUMO+20 375 0 -0.015179637 -0.4130589 LUMO+19 374 0 -0.015874008 -0.4319537 LUMO+18 373 0 -0.018789805 -0.5112966 LUMO+17 372 0 -0.018789807 -0.5112966 LUMO+16 371 0 -0.021827536 -0.5939575 LUMO+15 370 0 -0.028324622 -0.7707522 LUMO+14 369 0 -0.030143607 -0.8202493 LUMO+13 368 0 -0.030217716 -0.8222659 LUMO+12 367 0 -0.032073461 -0.8727633 LUMO+11 366 0 -0.033774531 -0.9190517 LUMO+10 365 0 -0.033774567 -0.9190527 LUMO+9 364 0 -0.034126365 -0.9286256 LUMO+8 363 0 -0.034127253 -0.9286498 LUMO+7 362 0 -0.040219886 -1.0944388 LUMO+6 361 0 -0.040219935 -1.0944401 LUMO+5 360 0 -0.052280985 -1.422638 LUMO+4 359 0 -0.053534541 -1.4567489 LUMO+3 358 0 -0.053536994 -1.4568157 LUMO+2 357 0 -0.064033971 -1.742453 LUMO+1 356 0 -0.069937961 -1.9031087 Continued on next page 190

Table C.7 Continued LUMO 355 0 -0.073686954 -2.005124 HOMO 354 2 -0.159459669 -4.3391183 HOMO-1 353 2 -0.162987928 -4.4351271 HOMO-2 352 2 -0.169482545 -4.6118546 HOMO-3 351 2 -0.16969372 -4.617601 HOMO-4 350 2 -0.215955565 -5.8764498 HOMO-5 349 2 -0.215958895 -5.8765404 HOMO-6 348 2 -0.220554146 -6.0015836 HOMO-7 347 2 -0.220579065 -6.0022616 HOMO-8 346 2 -0.222441479 -6.0529405 HOMO-9 345 2 -0.222441482 -6.0529406 HOMO-10 344 2 -0.224772897 -6.1163816 HOMO-11 343 2 -0.224773015 -6.1163848 HOMO-12 342 2 -0.240738461 -6.5508267 HOMO-13 341 2 -0.243398051 -6.6231978 HOMO-14 340 2 -0.243790756 -6.6338839 HOMO-15 339 2 -0.245529408 -6.681195 HOMO-16 338 2 -0.246722402 -6.713658 HOMO-17 337 2 -0.24819018 -6.7535983 HOMO-18 336 2 -0.254428517 -6.9233521 HOMO-19 335 2 -0.254429878 -6.9233891 HOMO-20 334 2 -0.258722108 -7.0401866 HOMO-21 333 2 -0.259000612 -7.0477651 HOMO-22 332 2 -0.259000617 -7.0477652 HOMO-23 331 2 -0.262057675 -7.130952 HOMO-24 330 2 -0.263458145 -7.1690608 HOMO-25 329 2 -0.274492495 -7.4693207 HOMO-26 328 2 -0.275889481 -7.5073346 HOMO-27 327 2 -0.275889665 -7.5073396 HOMO-28 326 2 -0.278458819 -7.5772499 HOMO-29 325 2 -0.281086638 -7.6487564 HOMO-30 324 2 -0.281760624 -7.6670965 # # 660 Alpha Frozen Core Electrons

191

Table C. 8. Selected orbital energy levels for W25Pt4.

# Orbital Occupancy Energy (Hart) Energy (eV) LUMO+30 483 0 -0.01401 -0.3811609 LUMO+29 482 0 -0.01401 -0.3811652 LUMO+28 481 0 -0.01427 -0.3882593 LUMO+27 480 0 -0.01427 -0.3882914 LUMO+26 479 0 -0.01509 -0.41074 LUMO+25 478 0 -0.0151 -0.4108329 LUMO+24 477 0 -0.01532 -0.4169866 LUMO+23 476 0 -0.01871 -0.5090164 LUMO+22 475 0 -0.01871 -0.5090164 LUMO+21 474 0 -0.01976 -0.537699 LUMO+20 473 0 -0.02478 -0.6742472 LUMO+19 472 0 -0.02949 -0.8024273 LUMO+18 471 0 -0.0296 -0.8055056 LUMO+17 470 0 -0.02999 -0.8161572 LUMO+16 469 0 -0.03 -0.8163367 LUMO+15 468 0 -0.03188 -0.8674448 LUMO+14 467 0 -0.03334 -0.9072543 LUMO+13 466 0 -0.0337 -0.9169009 LUMO+12 465 0 -0.0337 -0.916901 LUMO+11 464 0 -0.03392 -0.9230405 LUMO+10 463 0 -0.03392 -0.9230406 LUMO+9 462 0 -0.04013 -1.0919594 LUMO+8 461 0 -0.04013 -1.0919599 LUMO+7 460 0 -0.05188 -1.4118333 LUMO+6 459 0 -0.05196 -1.4138726 LUMO+5 458 0 -0.05342 -1.4536856 LUMO+4 457 0 -0.05342 -1.4536874 LUMO+3 456 0 -0.06249 -1.700483 LUMO+2 455 0 -0.06709 -1.8255283 LUMO+1 454 0 -0.07138 -1.9424583 LUMO 453 0 -0.07368 -2.0048296 HOMO 452 2 -0.15837 -4.309563 HOMO-1 451 2 -0.16106 -4.3826915 HOMO-2 450 2 -0.16351 -4.4493759 HOMO-3 449 2 -0.16947 -4.6114378 HOMO-4 448 2 -0.16951 -4.6126823 HOMO-5 447 2 -0.21516 -5.8548789 Continued on next page 192

Table C.8 Continued HOMO-6 446 2 -0.21575 -5.8707447 HOMO-7 445 2 -0.21575 -5.8707479 HOMO-8 444 2 -0.2198 -5.9811425 HOMO-9 443 2 -0.22036 -5.9963429 HOMO-10 442 2 -0.22036 -5.996374 HOMO-11 441 2 -0.22234 -6.0501751 HOMO-12 440 2 -0.22234 -6.0501751 HOMO-13 439 2 -0.22468 -6.1137361 HOMO-14 438 2 -0.22468 -6.1137364 HOMO-15 437 2 -0.23976 -6.5241757 HOMO-16 436 2 -0.24181 -6.5800897 HOMO-17 435 2 -0.24233 -6.5940182 HOMO-18 434 2 -0.24426 -6.6467826 HOMO-19 433 2 -0.24467 -6.6577285 HOMO-20 432 2 -0.24524 -6.6732201 HOMO-21 431 2 -0.24716 -6.7255009 HOMO-22 430 2 -0.24788 -6.7452068 HOMO-23 429 2 -0.25366 -6.9023881 HOMO-24 428 2 -0.25423 -6.9178734 HOMO-25 427 2 -0.25423 -6.9178737 HOMO-26 426 2 -0.25758 -7.0091589 HOMO-27 425 2 -0.25891 -7.0453391 HOMO-28 424 2 -0.25891 -7.0453391 HOMO-29 423 2 -0.26019 -7.08001 HOMO-30 422 2 -0.2625 -7.1429032 Frozen # 840 Alpha Cor e Electrons

193

APPENDIX D: SUPPORTING INFORMATION FOR CHAPTER 7

Table D. 1. Select bond lengths (Å) and angles (o) for 1-F.

Mo(1)-O(1) 2.0985(18) Mo(1)-O(2) 2.1028(19) Mo(1)-Mo(1)#1 2.1077(4) Mo(1)-O(4) 2.1128(18) Mo(1)-O(5) 2.1177(18)

O(1)-Mo(1)-O(2) 89.85(7) O(1)-Mo(1)-Mo(1)#1 92.43(5) O(2)-Mo(1)-Mo(1)#1 92.75(5) O(1)-Mo(1)-O(4) 89.58(7) O(2)-Mo(1)-O(4) 176.56(7) Mo(1)#1-Mo(1)-O(4) 90.66(5) O(1)-Mo(1)-O(5) 176.40(7) O(2)-Mo(1)-O(5) 88.78(7) Mo(1)#1-Mo(1)-O(5) 90.97(5) O(4)-Mo(1)-O(5) 91.58(7) C(8)-O(1)-Mo(1) 116.94(17) C(1)-O(2)-Mo(1) 116.46(16) C(18)-O(3)-C(15) 109.3(2) C(1)#1-O(4)-Mo(1) 118.00(16) C(8)#1-O(5)-Mo(1) 117.34(16)

194

Table D. 2. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for 1-F. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

______

x y z U(eq)

______

C(1) 4419(3) 5655(1) 6997(2) 26(1) C(2) 4139(3) 6045(2) 8069(3) 27(1) C(3) 4992(3) 5882(2) 9353(3) 37(1) C(4) 4742(4) 6253(2) 10350(3) 51(1) C(5) 3665(4) 6796(2) 10038(3) 53(1) C(6) 2811(3) 6985(2) 8782(3) 45(1) C(7) 3038(3) 6595(2) 7792(3) 34(1) C(8) 3443(3) 3764(2) 5186(2) 27(1) C(9) 2582(3) 3105(2) 5327(3) 28(1) C(10) 1128(3) 2975(2) 4457(3) 33(1) C(11) 311(3) 2378(2) 4624(3) 40(1) C(15) 9324(4) 4672(2) 8175(3) 49(1) C(16) 10986(4) 4715(3) 8410(5) 69(1) C(17) 11099(5) 4493(4) 7171(5) 96(2) C(18) 9753(4) 4082(3) 6471(4) 66(1) F(1) 3431(3) 7171(2) 11015(2) 86(1) Mo(1) 5985(1) 4767(1) 5677(1) 24(1) O(1) 4843(2) 3804(1) 5873(2) 28(1) O(2) 5584(2) 5242(1) 7264(2) 26(1) O(3) 8649(2) 4246(1) 7025(2) 39(1) O(4) 6497(2) 4254(1) 4163(2) 27(1) O(5) 7246(2) 5721(1) 5593(2) 27(1) C(12) 971(3) 1928(2) 5690(3) 39(1) C(13) 2407(3) 2027(2) 6550(3) 39(1) C(14) 3230(3) 2616(2) 6359(3) 34(1) F(2) 149(2) 1354(1) 5887(2) 55(1)

195

Table D. 3. Select bond lengths (Å) and angles (o) for 1-Cl.

Mo(1)-O(3) 2.1018(17) Mo(1)-Mo(1)#1 2.1085(4) Mo(1)-O(2) 2.1143(17) Mo(1)-O(4) 2.1185(16) Mo(1)-O(1) 2.1234(17)

O(3)-Mo(1)-Mo(1)#1 91.87(5) O(3)-Mo(1)-O(2) 91.98(6) Mo(1)#1-Mo(1)-O(2) 92.79(5) O(3)-Mo(1)-O(4) 87.77(6) Mo(1)#1-Mo(1)-O(4) 90.49(4) O(2)-Mo(1)-O(4) 176.72(6) O(3)-Mo(1)-O(1) 176.74(6) Mo(1)#1-Mo(1)-O(1) 91.39(4) O(2)-Mo(1)-O(1) 87.92(6) O(4)-Mo(1)-O(1) 92.14(6) C(8)-O(1)-Mo(1) 116.93(15) C(1)-O(2)-Mo(1) 116.34(15) C(8)#1-O(3)-Mo(1) 117.79(15) C(1)#1-O(4)-Mo(1) 118.35(15)

196

Table D. 4. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for 1-Cl. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

______

x y z U(eq)

______

C(1A) -450(4) 2307(2) 5110(2) 30(1) C(2A) -1644(4) 1390(3) 5706(3) 35(1) C(3A) 34(4) 1060(3) 6548(3) 40(1) C(4A) 1992(4) 1879(2) 6435(3) 32(1) O(5) 1352(3) 2830(2) 5905(2) 22(1) C(1) 2571(4) 5587(2) 3201(2) 18(1) C(2) 1312(4) 5885(2) 2190(2) 18(1) C(3) -812(4) 5509(2) 1968(2) 21(1) C(4) -1963(4) 5769(2) 1020(2) 24(1) C(5) -999(4) 6396(2) 273(2) 23(1) C(6) 1106(4) 6785(2) 485(2) 25(1) C(7) 2250(4) 6526(2) 1434(2) 23(1) C(8) 5408(4) 3102(2) 3604(2) 18(1) C(9) 5689(4) 2067(2) 2868(2) 20(1) C(10) 4260(4) 1009(2) 2707(2) 26(1) C(11) 4553(4) 36(2) 2053(2) 30(1) C(12) 6280(4) 118(2) 1562(2) 25(1) C(13) 7728(4) 1155(2) 1719(2) 25(1) C(14) 7421(4) 2132(2) 2362(2) 23(1) Cl(1) -2461(1) 6702(1) -946(1) 33(1) Cl(2) 6624(1) -1099(1) 713(1) 34(1) Mo(1) 3684(1) 4500(1) 5216(1) 16(1) O(1) 3919(2) 2992(1) 4144(1) 18(1) O(2) 1716(2) 4939(2) 3852(1) 18(1) O(3) 3304(2) 5936(2) 6302(1) 18(1) O(4) 5506(2) 4006(2) 6611(1) 18(1)

197

Table D. 5. Select bond lengths (Å) and angles (o) for 2-F.

Mo(1)-O(1) 2.1027(17) Mo(1)-Mo(1)#1 2.1038(4) Mo(1)-O(3) 2.1100(17) Mo(1)-O(4) 2.1125(17) Mo(1)-O(2) 2.1157(17)

O(1)-Mo(1)-Mo(1)#1 91.71(5) O(1)-Mo(1)-O(3) 89.72(7) Mo(1)#1-Mo(1)-O(3) 91.87(5) O(1)-Mo(1)-O(4) 176.28(6) Mo(1)#1-Mo(1)-O(4) 91.89(5) O(3)-Mo(1)-O(4) 89.24(7) O(1)-Mo(1)-O(2) 90.44(7) Mo(1)#1-Mo(1)-O(2) 91.68(5) O(3)-Mo(1)-O(2) 176.43(6) O(4)-Mo(1)-O(2) 90.38(7) C(1)-O(1)-Mo(1) 117.40(16) C(8)#1-O(2)-Mo(1) 116.87(16) C(8)-O(3)-Mo(1) 116.89(15) C(1)#1-O(4)-Mo(1) 116.58(16)

198

Table D. 6. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for 2-F. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

______

x y z U(eq)

______

C(1) 10346(3) -1697(2) 447(1) 31(1) C(2) 10490(3) -2629(2) 675(2) 34(1) C(3) 11288(3) -3188(2) 284(2) 43(1) C(4) 11372(3) -4061(2) 480(2) 50(1) C(5) 10664(3) -4359(2) 1077(2) 52(1) C(6) 9887(4) -3825(2) 1480(2) 59(1) C(7) 9785(3) -2954(2) 1272(2) 48(1) C(8) 11593(3) 543(2) 1266(1) 30(1) C(9) 12444(3) 853(2) 1969(2) 32(1) C(10) 12720(3) 1750(2) 2051(2) 34(1) C(11) 13439(3) 2028(2) 2731(2) 44(1) C(12) 13891(3) 1456(2) 3316(2) 50(1) C(13) 13610(3) 574(2) 3214(2) 48(1) C(14) 12879(3) 250(2) 2547(2) 37(1) C(15) 14682(5) 1812(3) 4051(2) 71(1) C(16) 13943(5) 2587(3) 4392(2) 75(1) C(17) 15101(4) 1140(3) 4637(2) 82(1) C(18) 12179(3) 2398(2) 1434(2) 41(1) C(19) 10787(3) 2692(2) 1596(2) 52(1) C(20) 13072(4) 3194(2) 1356(2) 51(1) C(21) 12559(3) -717(2) 2443(2) 45(1) C(22) 13572(5) -1177(2) 1979(2) 72(1) C(23) 12401(4) -1198(2) 3205(2) 64(1) C(24) 6024(3) 662(3) 834(2) 62(1) C(25) 6257(4) 1447(3) 1327(3) 75(1) C(26) 7054(6) 1145(3) 2050(3) 92(2) C(27) 7242(4) 169(3) 1925(2) 69(1) F(1) 10757(2) -5215(1) 1273(2) 74(1) Mo(1) 9168(1) 43(1) 326(1) 26(1) O(1) 9409(2) -1258(1) 707(1) 32(1) O(2) 7879(2) -371(1) -639(1) 32(1) O(3) 10349(2) 468(1) 1327(1) 31(1) O(4) 8841(2) 1363(1) 0(1) 31(1) O(5) 7050(2) 54(1) 1098(1) 52(1)

199

Table D. 7. Select bond lengths (Å) and angles (o) for 2-Cl.

Mo(1)-O(4) 2.103(2) Mo(1)-Mo(1)#1 2.1064(5) Mo(1)-O(2) 2.107(2) Mo(1)-O(1) 2.114(2) Mo(1)-O(3) 2.118(2)

O(4)-Mo(1)-Mo(1)#1 92.96(6) O(4)-Mo(1)-O(2) 90.02(9) Mo(1)#1-Mo(1)-O(2) 92.21(6) O(4)-Mo(1)-O(1) 89.66(9) Mo(1)#1-Mo(1)-O(1) 91.23(6) O(2)-Mo(1)-O(1) 176.56(8) O(4)-Mo(1)-O(3) 176.54(8) Mo(1)#1-Mo(1)-O(3) 90.49(6) O(2)-Mo(1)-O(3) 89.54(9) O(1)-Mo(1)-O(3) 90.57(9) C(1)-O(1)-Mo(1) 117.3(2) C(1)#1-O(2)-Mo(1) 116.7(2) C(8)-O(3)-Mo(1) 117.9(2) C(8)#1-O(4)-Mo(1) 116.2(2)

200

Table D. 8. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for 2-Cl. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

______

x y z U(eq)

______

C(1) 7019(3) 9348(1) 11387(4) 29(1) C(2) 8208(3) 9022(1) 12157(4) 32(1) C(3) 8609(4) 8906(1) 13619(4) 41(1) C(4) 9779(4) 8633(1) 14379(5) 48(1) C(5) 10556(4) 8481(1) 13648(4) 46(1) C(6) 10172(4) 8580(1) 12189(5) 49(1) C(7) 8995(4) 8851(1) 11449(4) 42(1) C(8) 2967(3) 9336(1) 9355(4) 29(1) C(9) 1856(3) 8969(1) 8975(4) 32(1) C(10) 2241(4) 8498(1) 9225(5) 44(1) C(11) 1188(4) 8162(1) 8837(5) 51(1) C(12) -205(4) 8278(1) 8201(5) 46(1) C(13) -565(4) 8753(1) 7956(4) 40(1) C(14) 441(3) 9107(1) 8347(4) 31(1) C(15) 3776(4) 8354(2) 9962(6) 58(1) C(16) 4135(7) 8164(3) 11502(6) 116(3) C(17) 4157(5) 7995(2) 9086(6) 77(2) C(18) -1285(5) 7881(2) 7788(6) 67(1) C(19) -1520(9) 7679(3) 6343(8) 142(4) C(20) -2589(5) 8001(2) 7887(7) 80(2) C(21) 68(3) 9626(1) 8083(4) 34(1) C(22) 26(4) 9794(2) 6616(4) 45(1) C(23) -1293(4) 9756(2) 8191(5) 46(1) C(24) 5202(4) 9074(1) 6598(4) 45(1) C(25) 5028(4) 8979(2) 5044(4) 57(1) C(26) 3836(5) 9296(2) 4161(5) 57(1) C(27) 3679(4) 9628(2) 5262(4) 51(1) Cl(2) 12067(1) 8152(1) 14610(1) 64(1) Mo(1) 5076(1) 9934(1) 9007(1) 25(1) O(1) 6634(2) 9419(1) 10021(2) 28(1) O(2) 3536(2) 10440(1) 7878(2) 30(1) O(3) 3492(2) 9415(1) 8450(2) 28(1) O(4) 6646(2) 10443(1) 9434(2) 28(1) O(5) 4915(2) 9570(1) 6594(3) 38(1)

201

Table D. 9. Select bond lengths (Å) and angles (o) for 2-Br.

Mo(1)-Mo(1)#1 2.1065(5) Mo(1)-O(1) 2.108(2) Mo(1)-O(4) 2.110(2) Mo(1)-O(2) 2.115(2) Mo(1)-O(3) 2.116(2)

Mo(1)#1-Mo(1)-O(1) 92.98(6) Mo(1)#1-Mo(1)-O(4) 92.65(6) O(1)-Mo(1)-O(4) 89.70(8) Mo(1)#1-Mo(1)-O(2) 90.80(6) O(1)-Mo(1)-O(2) 89.86(8) O(4)-Mo(1)-O(2) 176.54(8) Mo(1)#1-Mo(1)-O(3) 90.40(6) O(1)-Mo(1)-O(3) 176.56(8) O(4)-Mo(1)-O(3) 89.50(8) O(2)-Mo(1)-O(3) 90.74(8) C(17)-O(4)-Mo(1) 116.2(2) C(1)#1-O(3)-Mo(1) 118.2(2) C(24)-O(5)-C(27) 105.3(3) C(17)#1-O(2)-Mo(1) 118.0(2) C(1)-O(1)-Mo(1) 115.9(2)

202

Table D. 10. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for 2-Br. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

______

x y z U(eq)

______

C(7) -1836(4) 8912(4) 6812(2) 20(1) C(12) -1572(5) 10235(7) 9401(4) 70(2) C(9) -1180(5) 4309(5) 9202(3) 41(1) C(10) 1162(5) 4368(5) 8297(3) 44(1) C(27) 4784(4) 3907(4) 4318(3) 33(1) C(26) 5991(4) 4178(5) 3626(3) 41(1) C(25) 5178(4) 5633(5) 2941(3) 35(1) C(24) 3585(4) 5826(4) 3117(2) 29(1) C(1) -813(4) 6562(3) 6333(2) 19(1) C(2) -1284(4) 7400(4) 7077(2) 20(1) C(3) -1194(4) 6627(4) 8031(2) 22(1) C(4) -1673(4) 7439(4) 8710(2) 26(1) C(5) -2235(4) 8947(4) 8477(2) 24(1) C(6) -2311(4) 9669(4) 7522(2) 24(1) C(8) -518(4) 4969(4) 8282(3) 31(1) C(11) -2732(4) 9771(4) 9249(3) 32(1) C(13) -4218(5) 11070(5) 9092(3) 44(1) C(14) -1981(4) 9696(4) 5772(2) 23(1) C(16) -3412(4) 9889(4) 5413(3) 33(1) C(15) -1849(4) 11134(4) 5531(3) 31(1) C(17) 1281(4) 2475(4) 6320(2) 20(1) C(18) 1994(4) 1043(4) 6995(2) 21(1) C(19) 3438(4) 548(4) 7257(3) 29(1) C(20) 4117(4) -804(4) 7844(3) 32(1) C(21) 3340(4) -1669(4) 8171(2) 28(1) C(22) 1916(4) -1214(4) 7932(3) 30(1) C(23) 1246(4) 142(4) 7344(2) 27(1) Mo(1) 1007(1) 5115(1) 4880(1) 17(1) O(4) 2062(2) 3184(2) 5905(2) 20(1) O(3) 1695(2) 3891(2) 3847(2) 19(1) O(5) 3464(3) 5237(3) 4114(2) 26(1) O(2) 69(2) 7071(2) 3843(2) 20(1) O(1) 453(2) 6324(2) 5907(2) 19(1) Br(1) 4277(1) -3549(1) 8980(1) 43(1)

203

Table D. 11. Select bond lengths (Å) and angles (o) for 2-I.

Mo(1)-O(1) 2.100(2)

Mo(1)-Mo(1)#1 2.1080(6) Mo(1)-O(4) 2.109(2) Mo(1)-O(2) 2.113(2) Mo(1)-O(3) 2.116(2)

O(1)-Mo(1)-Mo(1)#1 93.15(7) O(1)-Mo(1)-O(4) 89.81(10) Mo(1)#1-Mo(1)-O(4) 91.53(7) O(1)-Mo(1)-O(2) 89.40(10) Mo(1)#1-Mo(1)-O(2) 92.02(7) O(4)-Mo(1)-O(2) 176.40(9) O(1)-Mo(1)-O(3) 176.51(9) Mo(1)#1-Mo(1)-O(3) 90.34(7) O(4)-Mo(1)-O(3) 89.91(10) O(2)-Mo(1)-O(3) 90.67(10) C(1)-O(4)-Mo(1) 117.2(2) C(6)-C(5)-C(4) 121.6(4) C(6)-C(5)-I(2) 119.1(3) C(4)-C(5)-I(2) 119.3(3) C(1)#1-O(2)-Mo(1) 116.9(2) C(8)-O(1)-Mo(1) 115.9(2)

204

Table D. 12. Atomic coordinates (x104) and isotropic displacement parameters (Å2 X 103) for 2-I. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

______

x y z U(eq)

______

O(5) 6618(3) 4850(3) 892(2) 30(1) C(25) 6700(4) 4159(5) 1855(3) 33(1) C(22) 11838(5) -1141(5) -520(3) 39(1) C(23) 13334(5) 252(5) -494(3) 39(1) C(19) 11771(5) 289(5) -4245(3) 41(1) C(24) 5253(5) 6097(5) 741(4) 44(1) C(18) 7996(5) 5454(5) -3876(4) 49(1) C(17) 10205(6) 5793(5) -3484(4) 49(1) C(21) 11581(6) -1091(5) -4050(3) 53(1) C(20) 13270(7) 108(8) -4559(5) 77(2) C(26) 5185(5) 4260(6) 2053(4) 47(1) C(27) 4241(5) 5719(6) 1454(4) 56(2) Mo(1) 9020(1) 4883(1) 169(1) 18(1) I(2) 15068(1) -3457(1) 4052(1) 40(1) O(4) 10113(3) 2966(3) 1174(2) 20(1) C(5) 13876(4) -1470(4) 3139(3) 25(1) O(2) 7807(3) 6775(3) -826(2) 20(1) O(1) 9260(3) 3666(3) -825(2) 21(1) C(1) 11496(4) 2533(4) 1284(3) 20(1) C(2) 12307(4) 1152(4) 1955(3) 21(1) C(9) 10663(4) 2587(4) -2043(3) 22(1) O(3) 8662(3) 6090(3) 1197(2) 21(1) C(3) 11643(4) 234(4) 2348(3) 30(1) C(10) 10173(4) 3333(4) -2956(3) 28(1) C(8) 10393(4) 3441(4) -1307(3) 21(1) C(15) 11861(4) 349(4) -788(3) 27(1) C(14) 11440(4) 1094(4) -1801(3) 24(1) C(4) 12423(5) -1079(4) 2944(3) 34(1) C(12) 11357(4) 1067(5) -3447(3) 30(1) C(13) 11790(4) 357(4) -2520(3) 29(1) C(16) 9249(5) 4962(5) -3177(3) 36(1) C(7) 13765(4) 748(4) 2177(3) 29(1) C(11) 10535(5) 2544(5) -3643(3) 33(1) C(6) 14555(4) -586(4) 2767(3) 30(1)

205

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