Mixed-Valence Systems: Fundamentals, Synthesis, Electron Transfer, and Applications

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Mixed-Valence Systems Comprehensive overview on the advanced development of mixed-valence chemistry Mixed-Valence Systems: Fundamentals, Synthesis, Electron Transfer, and Applications covers all topics related to the theory and experimental results of mixed-valence systems, including the design, synthesis, and applications of mixed-valence compounds containing inorganic, organometallic and organic redox-active centers. The text also covers the recent advances in mixed-valence chemistry, including the development of new mixed-valence systems, transition of mixed valency, better understanding of the spectral characteristics of intervalence charge transfer, and controllable electron transfer related to molecular electronics. In Mixed-Valence Systems , readers can expect to find detailed information on sample topics such as: Characterization and evaluation of mixed-valence systems, electron paramagnetic resonance spectroscopy, and electrochemical methods Optical analysis, important issues in mixed-valence chemistry, transition of mixed valency from localized to delocalized, and solvent control of electron transfer Theoretical background, potential energy surfaces from classical two-state model, and quantum description of the potential energy surfaces Reorganization energies, electronic coupling matrix element and the transition moments, generalized Mulliken–Hush theory, and analysis of the band shape of intervalence charge transfer Strengthening the relationship of mixed-valence electron transfer and molecular electronics, Mixed-Valence Systems is of immense value to researchers and professionals working in the field of electron transfer, molecular electronics, and optoelectronics. Cover Halt Title Mixed-Valence Systems: Fundamentals, Synthesis, Electron Transfer, and Applications Copyright Dedication Contents Preface 1. Introduction and Fundamentals of Mixed‐Valence Chemistry 1.1 Introduction 1.2 Brief History 1.3 Diversity of Mixed‐Valence Systems – Some Examples 1.4 Characterization and Evaluation of Mixed‐Valence Systems 1.4.1 Electron Paramagnetic Resonance Spectroscopy 1.4.2 Electrochemical Methods 1.4.3 Optical Analysis 1.5 Important Issues in Mixed‐Valence Chemistry 1.5.1 System Transition in Mixed Valency from Localized to Delocalized 1.5.2 Solvent Control of Electron Transfer 1.6 Theoretical Background 1.6.1 Potential Energy Surfaces from Classical Two‐State Model 1.6.2 Quantum Description of the Potential Energy Surfaces 1.6.3 Reorganization Energies 1.6.4 Electronic Coupling Matrix Element and the Transition Moments 1.6.5 The Generalized Mulliken–Hush Theory (GMH) 1.6.6 Analysis of IVCT Band Shape 1.6.7 Rate Constant Expressions of Electron Transfer Reaction – The Marcus Theory 1.6.8 McConnell Superexchange Mechanism and the CNS Model 1.7 Conclusion and Outlook Acknowledgments References 2. Conceptual Understanding of Mixed‐Valence Compounds and Its Extension to General Stereoisomerism 2.1 Introduction 2.2 Modeling MV and Related Chemistry 2.2.1 Origins Within Chemical Bonding Theory 2.2.2 Coupled Harmonic Oscillator Model 2.2.3 Intermolecular and Intramolecular Contributions to the Reorganization Energy 2.2.4 Effects of Electric Fields on MV Optical Band Shapes 2.2.5 Non‐adiabatic Effects 2.2.6 MV Complexes as Potential Quantum Qubits 2.2.7 Entanglement as a Measure of the Failure of the BO Approximation 2.2.8 Further Reading 2.3 Some Traditional Mixed‐Valence Example Molecules and Iconic Model Systems 2.3.1 Photochemical Charge Separation 2.3.2 MV Excited States in a Bis–Metal Complex 2.3.3 Hole Transport in a Molecular Conducting Material 2.3.4 Ground‐State Delocalization in the Creutz–Taube Ion 2.3.5 Photochemical Charge Separation During Bacterial Photosynthesis 2.3.6 Prussian Blue 2.4 Applications to Stereoisomerism 2.4.1 Breakdown of Aromaticity in the (π,π*) 3A1 Triplet Ground State of Pyridine 2.4.2 Isomerism of BNB 2.4.3 Isomerism of Ammonia and Related Molecules 2.4.4 Proton Transfer in [NH3·H·NH3]+ 2.4.5 Aromaticity in Benzene 2.5 Conclusion and Outlook References 3. Quantum Chemical Approaches to Treat Mixed‐Valence Systems Realistically for Delocalized and Localized Situations 3.1 Introduction and Scope 3.2 How Did We Start 3.3 Moving to Transition Metal MV Systems, Getting into Conformational Aspects 3.4 More Recent Work on Organic MV Systems and More General Use for Charge Transfer Questions 3.5 More Recent Insights into Conformational Aspects for Transition Metal Complexes 3.6 Other Applications to Organometallic MV Systems 3.7 Limitations of the Simple Computational Protocols, Gas‐Phase Benchmarks, and Improved Electronic Structure Methods 3.8 More Advanced Treatments of Environmental Effects 3.9 Conclusion and Outlook Acknowledgement References 4. Mixed Valency in Ligand‐Bridged Diruthenium Complexes 4.1 Introduction 4.2 RuIIRuIII Mixed‐Valent Systems 4.2.1 Pyrazine‐Derived Bridges 4.2.2 Other Bridging Ligands 4.3 RuIIIRuIV Mixed‐Valent Systems 4.4 RuIIRuI and RuIRu0 Mixed‐Valent Systems 4.5 Conclusion and Outlook Acknowledgment References 5. Electronic Communication in Mixed‐Valence (MV) Ethynyl, Butadiynediyl, and Polyynediyl Complexes of Iron, Ruthenium, and Other Late Transition Metals 5.1 Introduction 5.2 Iron–Ethynyl Complexes 5.2.1 Dinuclear Iron–Ethynyl Complexes with Butadiynediyl Bridge 5.2.2 Dinuclear Iron–Ethynyl Complexes with Diynediyl, Polycyclic Aromatic Hydrocarbons and Heterocycles in the C4 Bridge Core 5.2.3 Dinuclear Iron–Ethynyl Complexes with Non‐conjugated C4 Bridge Core 5.2.4 Functionalized Dinuclear Iron–Ethynyl Complexes 5.3 Ruthenium–Ethynyl Complexes 5.3.1 Dinuclear Ruthenium–Ethynyl Complexes with Cp′(L2)Ru‐Based Termini 5.3.2 Dinuclear Ruthenium–Ethynyl Complexes with Ru(dppe)2X‐Based Termini 5.3.3 Ruthenium–Ethynyl Complexes with Alternating Polyyndiyl and Capped Ru–Ru Units 5.3.4 Ruthenium–Ethynyl Complexes with Other Ruthenium–Ethynyl Termini and Core Units 5.4 Other Transition Metal–Ethynyl Complexes 5.4.1 Dinuclear Group 6 (Cr and Mo) Metal–Ethynyl Complexes 5.4.2 Dinuclear Group 7 (Mn and Re) Metal–Polyynediyl Complexes 5.4.3 Dinuclear Group 8 (Os) and Group 9 (Co) Metal–Polyyndiyl Complexes 5.5 Concluding Remarks and Outlook Acknowledgment References 6. Electron Transfer in Mixed‐Valence Ferrocenyl‐Functionalized Five‐ and Six‐Membered Heterocycles 6.1 Introduction 6.2 Ferrocenyl‐Functionalized Five‐Membered Heterocycles 6.2.1 Five‐Membered Heterocyclic Compounds with Group 13 Elements 6.2.2 Five‐Membered Heterocyclic Compounds with Group 14 Elements 6.2.3 Five‐Membered Heterocyclic Compounds with Group 15 Elements 6.2.4 Five‐Membered Heterocyclic Compounds with Group 16 Elements 6.2.5 Five‐Membered Heterocyclic Compounds with Transition Metal Elements 6.3 Ferrocenyl‐Functionalized Six‐Membered Heterocycles 6.4 Conclusion and Outlook Acknowledgment References 7. Electronic Coupling and Electron Transfer in Mixed‐Valence Systems with Covalently Bonded Dimetal Units 7.1 Introduction 7.2 Synthesis and Characterization 7.3 d(δ)(M2)‐p(π)(Ligand) Conjugation 7.4 Electronic and Intervalence Transitions and DFT Calculations 7.5 Transition in Mixed Valency Between Robin–Day Classes 7.6 Distance Dependence of Electronic Coupling and Electron Transfer 7.7 Conformational Effects of Electronic Coupling and Electron Transfer 7.8 Class III and Beyond 7.9 Cross‐Conjugation and Quantum Destructive Effect 7.10 Electronic Coupling and Electron Transfer Across Hydrogen Bonds 7.11 Mixed‐Valence Diruthenium Dimers 7.12 Conclusions and Outlook Acknowledgments References 8. Mixed‐Valence Electron Transfer of Cyanide‐Bridged Multimetallic Systems 8.1 Introduction 8.2 Dinuclear Cyanide‐Bridged Mixed‐Valence Complex 8.3 Trinuclear Cyanide‐Bridged Mixed‐Valence Complex 8.4 Tetranuclear and Higher Nuclear Cyanide‐Bridged Mixed‐Valence Complex 8.5 Conclusion and Outlook Acknowledgment References 9. Organic Mixed‐Valence Systems: Toward Fundamental Understanding of Charge/Spin Transfer Materials 9.1 A Brief Sketch of the History of Organic Mixed‐Valence Systems 9.2 A Glossary for This Chapter 9.2.1 Hush Analysis 9.2.2 Mulliken–Hush Two‐State Analysis 9.2.3 Mulliken–Hush Two‐Mode Analysis 9.2.4 Generalized Mulliken–Hush Three‐State Analysis 9.3 Relationship Between Bridging Units and Electronic Coupling 9.4 Where to Attach Redox Centers 9.5 Through‐Bond or Through‐Space? 9.6 Control of Spin States Through Mixed‐Valence States 9.7 Future Prospects Acknowledgment References 10. Mixed‐Valence Complexes in Biological and Bio‐mimic Systems 10.1 Introduction 10.2 Mixed‐Valence Iron–Sulfur Clusters in Biological and Bio‐mimic Systems 10.2.1 Basic FeS Clusters 10.2.2 [FeFe]‐Hydrogenase 10.2.3 Nitrogenases 10.2.4 Carbon Monoxide Dehydrogenase 10.3 Mixed‐Valence Systems in Multiheme and Other Multiiron‐Contained Biological Systems and Their Mimics 10.4 Mixed‐Valence Multicopper Cofactors in Biological and Mimicking Systems 10.5 OEC and Other Mixed‐Valence Multimanganese Cofactors 10.6 Summary Acknowledgement References 11. Control of Electron Coupling and Electron Transfer Through Non‐covalent Interactions in Mixed‐Valence Systems 11.1 Introduction 11.2 Electronic Coupling Through Hydrogen Bonds 11.2.1 Electronic Coupling Between Transition Metal Centers Through Hydrogen Bonds 11.2.2 Electronic Coupling Between Organic Fragments Through Hydrogen Bonds 11.3 Modulation of Electronic Coupling via Host–Guest or Through‐Space Interaction 11.4 Conclusion Acknowledgment References 12. Stimulus‐Responsive Mixed‐Valence and Related Donor–Acceptor Systems 12.1 Introduction 12.2 Photoswitchable Compounds 12.3 Anion‐Responsive Compounds 12.4 Proton‐Responsive Compounds 12.5 Conclusion and Outlook Acknowledgement References 13. Mixed Valency in Extended Materials 13.1 Introduction 13.1.1 Fundamental Aspects of Mixed Valency in the Solid State 13.1.2 Quantum Mechanical Considerations in Mixed Valency and IVCT 13.1.3 Marcus–Hush Theory and the Quantification of CT 13.1.4 Classifications of Mixed Valency 13.1.5 Organic Mixed Valency 13.2 Electron Transfer in Extended MV Materials 13.2.1 Introduction to Extended Materials 13.2.2 Organic‐Based Mixed Valency in Extended Frameworks 13.2.2.1 Thiazolo[5,4‐d]thiazole‐Based Compounds 13.2.2.2 Tetrathiafulvalene (TTF)‐Based Compounds 13.2.2.3 Tetraoxolene‐Based Compounds 13.2.2.4 Naphthalenediimide (NDI)‐Based Compounds 13.2.2.5 Phenalenyl‐Based Compounds 13.2.2.6 Covalent‐Organic Frameworks (COFs) 13.2.3 Metal‐Based Mixed Valency 13.2.3.1 First‐Row Transition Metals 13.2.3.2 Other Metals 13.2.3.3 Catalysis in Uncoupled MV Systems 13.3 Conclusion References 14. Near‐Infrared Electrochromism Based on Intervalence Charge Transfer 14.1 Introduction 14.2 Near‐Infrared Electrochromic Materials 14.2.1 Inorganic NIR Electrochromic Materials 14.2.2 Organic NIR Electrochromic Materials 14.2.2.1 Viologen Derivatives 14.2.2.2 Triphenylamine Derivatives 14.2.2.3 Organic Conducting Polymers 14.2.2.4 Covalence‐Organic Framework (COF) 14.2.3 Organic–Inorganic Hybrid NIR Electrochromic Materials 14.2.3.1 Metal Complexes 14.2.3.2 Conducting Polymers of Metal Complexes 14.2.3.3 Monolayer and Multilayer Assembled Films 14.3 Potential Applications of NIR Electrochromic Materials 14.3.1 Smart Windows 14.3.2 Molecular Logic Gates and Optical Storage 14.3.3 Optical Communication 14.3.4 Military Camouflage 14.4 Summary and Outlook Acknowledgment References 15. Manipulation of Metal‐to‐Metal Charge Transfer Toward Switchable Functions 15.1 Introduction 15.2 Switchable Cyanide‐Bridged MMCT Systems 15.3 Cyanide‐Bridged MMCT Complexes Showing Switchable Functional Properties 15.3.1 Modulating Molecular Nanomagnet Behavior 15.3.2 Modulating Molecular Electric Dipole 15.3.3 Modulating Thermal Expansion Behavior 15.3.4 Modulating Photochromic Behavior 15.4 Conclusion and Outlook References Index