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Mixed-Valence Systems

E-BookEPUB2 - DRM Adobe / EPUBE-Book
512 Seiten
Englisch
Wiley-VCH GmbHerschienen am09.03.20231. Auflage
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.


Yu-Wu Zhong is Professor at Institute of Chemistry, Chinese Academy of Sciences. His research interests focus on mixed-valence chemistry, near-infrared electrochromim, organic nanophotonics and perovskite solar cells.
Chun Y. Liu is Professor at Jinan University, Guangzhou, China. His research topics include mixed valency, electron transfer, solar-chemical energy conversion and molecular electronics.
Jeffrey R. Reimers, Professor, holds a joint position at Shanghai University and University of Technology Sydney, and Director of the International Centre for Quantum and Molecular Structures. His current research interests include molecular electronics, nanophotonics, 2D materials, and the conceptual basis of chemistry.mehr
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Produkt

KlappentextMixed-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.


Yu-Wu Zhong is Professor at Institute of Chemistry, Chinese Academy of Sciences. His research interests focus on mixed-valence chemistry, near-infrared electrochromim, organic nanophotonics and perovskite solar cells.
Chun Y. Liu is Professor at Jinan University, Guangzhou, China. His research topics include mixed valency, electron transfer, solar-chemical energy conversion and molecular electronics.
Jeffrey R. Reimers, Professor, holds a joint position at Shanghai University and University of Technology Sydney, and Director of the International Centre for Quantum and Molecular Structures. His current research interests include molecular electronics, nanophotonics, 2D materials, and the conceptual basis of chemistry.
Details
Weitere ISBN/GTIN9783527835270
ProduktartE-Book
EinbandartE-Book
FormatEPUB
Format Hinweis2 - DRM Adobe / EPUB
FormatFormat mit automatischem Seitenumbruch (reflowable)
Erscheinungsjahr2023
Erscheinungsdatum09.03.2023
Auflage1. Auflage
Seiten512 Seiten
SpracheEnglisch
Dateigrösse46034 Kbytes
Artikel-Nr.11214838
Rubriken
Genre9201

Inhalt/Kritik

Inhaltsverzeichnis
1. Introduction and Fundamentals of Mixed-Valence Chemistry
2 The Conceptual Understanding of Mixed-Valence Compounds and Its Extension to General Stereoisomerism
3 Quantum-Chemical Approaches to Treat Mixed-Valence Systems Realistically for Delocalized and Localized Situations
4 Mixed Valency in Ligand Bridged Diruthenium Complexes
5 Electronic Communication in Mixed-Valence (MV) Ethynyl, Butadiyndiyl and Polyynediyl Complexes of Iron, Ruthenium and Other Late Transition Metals
6 Electron Transfer in Mixed-Valence Ferrocenyl-Functionalized 5- and 6-Membered Heterocycles
7 Electronic Coupling and Electron Transfer in Mixed-Valence Systems with Covalently-Bonded Dimetal Units
8 Mixed-Valence Electron Transfer of Cyanide-Bridged Multimetallic Systems
9 Organic Mixed-Valence Systems: Towards Fundamental Understanding of Charge/Spin Transfer Materials
10 Mixed-Valence Complexes in Biological and Bio-Mimic Systems
11 Control of Electron Coupling and Electron Transfer through Non-Covalent Interactions in Mixed-Valence Systems
12 Stimulus-Responsive Mixed-Valence and Related Donor-Acceptor Systems
13 Mixed Valency in Extended Materials
14 Near-Infrared Electrochromism Based on Intervalence Charge Transfer
15 Manipulate Metal-to-Metal Charge Transfer towards Switchable Functionsmehr
Leseprobe

1
Introduction and Fundamentals of Mixed-Valence Chemistry

Chun Y. Liu and Miao Meng

Jinan University, College of Chemistry and Materials Science, Department of Chemistry, 601 Huang-Pu Avenue West, Guangzhou 510632, China
1.1 Introduction

The term mixed valence (MV) is used to describe chemical systems in condensed media and solids in which the same chemical element exists in different oxidation states [1-3]. Thus, MV compounds refer to the category of unimolecular systems consisting of more than one redox center derived from the same element but formally having different oxidation levels in the ground state. In this context, molecules or solids having the same chemical constitutions but different oxidation states for the nonequivalent atoms should be viewed as distinct chemical identities or materials, but those having the same oxidation level are chemically identical. Prussian blue, the prototype of MV compound, is identical to Turnbull's blue [4]. It should be addressed that in MV compounds, the oxidation states of individual redox-active atoms that share the same elemental redox potential depend upon the electronic properties of the chemically bonded atoms or groups. For example, a high oxidation level is given to a redox center surrounded by more or stronger electron-withdrawing atoms or groups, and vice versa, a lesson learned from text book chemistry. However, mixed valency of MV compounds, which concerns charge distribution over the molecular ground state, is a very comprehensive issue pertaining to electrons and nuclei in motion that compasses a number of fundamental chemical problems, including energetic, dynamic, kinetic, and mechanistic of chemical transformations [5-8]. Moreover, MV compounds possess a unique optical property resulting from charge transfer between the spatially separated (chemically bonded or nonbonded) atoms with different valence electron shells. The interplays of electronic and nuclear dynamics within the molecule and between molecules (MV molecules and solvent molecules) are implicated through their optical behaviors, which are translated into the dynamics and energetics of the interpenetrated chemical and physical systems. With its enriched scientific contents, mixed-valent chemistry has evolved into one of the major playgrounds in modern chemistry in its own right for experimental and theoretical practitioners [6-10].

The attraction of mixed-valence systems is largely enforced by the fact that the valences of the discrete redox centers are intramolecularly self-exchangeable, thus representing the most elementary chemical reaction: intramolecular electron transfer (ET). In the middle of last century, the theoretical framework for ET was constructed and expanding rapidly, as marked by a series of profound progresses made in a relatively short period of time. Kubo and Toyozawa derived the general expression of activation energy (1955) [11]; Levich and Dogonadze presented the rate equation for ET reaction in the nonadiabatic limit (1960) [12, 13]; Marcus introduced the dielectric continuum model of solvation and the classical ET kinetic formalism (1956) [14, 15]; McConnell developed the superexchange model (1961) [16]; and Hush described the intramolecular effects using coupled harmonic surfaces (1958) [17] and calculations of the electronic coupling integral from intervalence optical parameters (1967) [5]. In the two-state description, the energy profiles of initial and final states of the system are approximated with a harmonic oscillator, which models the incorporated electron-nuclei dynamics in chemical transformation from reactant to product along the reaction coordinate. This simplified theoretical model on ET demands an experimental model that has single transferring electrons and well-defined electronic configuration. Thus, research work on MV chemistry gained a strong impetus to experimentally monitor the ET processes and to validate the semiclassical theories.

The follow-up experimental study was pioneered by Taube and Creutz with the elegantly designed, pyrazine (pz)-bridged diruthenium complex (I), {[(Ru(NH3)5](μ-pz)[(Ru(NH3)5]}5+, known as the Creutz-Taube ion [18], in which the two bridged Ru ions have formal oxidation numbers +2 and +3.

In a formal sense, the Ru2+(d6) and Ru3+(d5) centers in I serve the electronic donor (D) and acceptor (A), respectively, and electron self-exchange crossing the pz bridge (B) occurs without change of the free energy (ÎG = 0). In the mixed-valent D-B-A molecular system, electron migrating from D to A and nuclear motion conform energetically and dynamically to the semiclassical two-state models [19, 20]. The Creutz-Taube ion allowed the first observation of Frank-Condon transition that induces ET between two metal centers in a molecular complex, namely, intervalence charge transfer or IVCT [18, 21]. Inspired by the Creutz-Taube complex, a large number of MV compounds in form of D-B-A with various transition metal complex and organic charge-bearing units for the D and A sites have been synthesized, and studied in terms of electronic coupling (EC) and ET [6, 8, 22-24].

Electron transfer in MV systems may proceed via one of the two reaction pathways, thermal or optical [6, 22, 25-27]. By thermal ET pathway, the system overcomes the thermal energy barrier (ÎG*) and reaches the transition state through thermal fluctuations. In the transition state, designated as [D-B-A]â  and [A-B-D]â  in Figure 1.1 for the forward and reverse reactions, respectively, the system has an averaged nuclear configuration for the MV molecule (the activated complex) and solvation. From the reactant to the product, the system experiences an adiabatic process. Optical ET in MV compounds is initiated by vertical transition of the reactant state (with the extra electron on the donor) to the vibrational excited states of the product (with the extra electron transferred to the acceptor) (Figure 1.1). This transition occurs between two diabatic states and is governed by the Frank-Condon principle. Radiationless relaxation of the system from the nuclear excited state to the ground states completes the ET process [6, 19, 25].

For the ET event to occur, no matter which pathway is taken, the donor and acceptor electronic states must be coupled. It is the extent of coupling that controls the ET dynamics and kinetics, which is quantified by the coupling matrix element in quantum mechanics, i.e. Hab. Hush demonstrated that this crucial quantity can be derived from the IVCT spectrum of the MV compound [5, 6, 9, 19]. The Hush model connects the spectral data (transition energy, intensity, and absorption bandwidth) of the molecular system and the energetic parameters of the ET reaction (coupling integral and thermal ET barrier), and paves the way to optical determination of ET rate constant (kET). This optically determined coupling integral (Hab) can be incorporated into adiabatic and nonadiabatic ET kinetic expressions in the classical and semiclassical formalisms, which have been successfully applied in strongly and weakly coupled MV systems, respectively. Advances in time-resolved spectroscopic techniques allow the photoexcited states to be monitored, thus providing a powerful means for study of the photoinduced ET process in systems involving electronic excited states, D*-B-A or D-B-A*. Optical study of MV compounds and transient spectroscopic investigations of photoinitiated ET are complemented in development, validation, and refinement of the contemporary ET theories [19, 20, 25]. The gained understanding allows control of electron (charge) transfer in molecular systems and elucidation of the long-range charge transport processes in biological system and is beneficial to development of innovative technologies such as conductive materials, molecular electronics, and catalysts for solar-chemical energy conversion.

Figure 1.1 Optical (top) and thermal (bottom) ET pathways in mixed-valence D-B-A compounds. [A-B-D]* represents the vibrational excited state of the product. EIT is the intervalence charge transfer transition energy. [D-B-A]â  and [A-B-D]â  refers to the transition complex for the reactant and product, respectively. ÎG*F and ÎG*R is activation energy of the forward and reverse ET reaction, respectively.
1.2 Brief History

Historically, mixed-valence solids were found several centuries ago in various minerals, such as metal oxides, sulfates, and phosphates, in which the metal elements exist in different valence states [1, 3, 28]. These minerals usually show intense colors. The coloration of vivianite crystal with the chemical formula Fe3(PO4)2·8H2O is one of the interesting examples [5]. Vivianite is colorless when freshly exposed, as expected for the Fe2+ ion; after being exposed to air, it shows varying colors from light blue, light green, to dark blue or green, depending on the length of exposure due to oxidation of Fe2+ to Fe3+. As early as in...
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