Main description:

Mixed valency is one of various names used to describe compounds which contain ions of the same element in two different formal states of oxidation. The existence of mixed valency systems goes far back into the geological evolutionary history of the earth and other planets, while a plethora of mixed valency minerals has attracted attention since antiquity. Indeed, control of the oxidation states of Fe in its oxides (FeO, Fe304' Fe203) was elegantly used in vase painting by the ancient Greeks to produce the characteristic black and red Attic ceramics (Z. Goffer, "Archaeological Chemistry", Wiley, New York, 1980). It was, however, only 25 years ago that two reviews of mixed valency appeared in the literature almost simultaneously, signalling the first attempt to treat mixed valency systems as a separate class of compounds whose properties can be correlated with the molecular and the electronic structure of their members. Then mixed valency phenomena attracted the interest of disparate classes of scientists, ranging from synthetic chemists to solid state physicists and from biologists to geologists. This activity culminated with the NATO ASI meeting in Oxford in 1979. The 1980's saw again a continuing upsurge of interest in mixed valency. Its presence is a necessary factor in the search for highly conducting materials, including molecular metals and superconductors. The highly celebrated high T c ceramic superconducting oxides are indeed mixed valency compounds.

Contents:

Mixed Valency Systems: Retrospect And Prospect.- Vibronic Coupling Models Of Mixed Valency: Relation Of The PKS And MO Models For One- And Two-Electron Systems.- Electric Field Perturbation Of Electronic (Vibronic) Absorption Envelopes: Application To Characterization Of Mixed Valence States.- Solvent And Temperature Effects In Mixed Valence Chemistry.- Electron Transfer In Mixed Valence Complexes In The Solid State.- Photoredox Chemistry Of Two-Electron Mixed Valence Systems.- How To Design Fast Two-Electron Transfer Reagents: 37-Electron Mixed Valence Fe(I)Fe(II)-Bisandwiches As Key Intermediates.- Magnetic And Optical Phenomena In Biological Iron-Sulfur Mixed Valence Complexes And Their Chemical Models. A Theoretical Approach.- Mixed Valency In Multinuclear Manganese Enzymes And Clusters.- Mixed Valence Iron And Chromium Fluorides. Bronzes And Related Compounds. Chemistry, Structure And Magnetism.- Mixed Valency Minerals: Influences Of Crystal Structures On Optical And Moessbauer Spectra.- Valency Disproportionation In Inorganic Solids.- Superconductivity By Local Pairs (Bipolarons) In Doped Metal Oxide Semiconductors.- A Comparison Between Conducting C.T. Crystalline Salts And L.B. Films.- Optical Spectroscopic Probes Of Mixed Valence Systems.- Inelastic Neutron Scattering Studies Of Mixed Valency Systems.- Moessbauer Emission Spectroscopy Of Mixed Valency After Nuclear Decay In Iron Complexes.- Intramolecular Electron Transfer. Applications In Molecular Electronics.- Vibronic Coupling Models For Mixed Valence Line Shapes: Going Beyond The PKS Approach.- Mixed Valency Oligomers: Model Pathways For The Control Of Their Properties.- The Effects Of Second Order Vibronic Coupling On The Symmetric Dimer And Trimer.- Semiclassical Approach To The Vibronic Problem For The Creutz-Taube Ion.- A New Spin Hamiltonian For Mixed Valence Systems Including Transfer, Exchange And Exchange-Transfer Terms.- An Example Of The Influence Of The Ligand Held On The Electron Localisation: The Mixed Valence Ferrocene-Ferricinium.- A First Stable Organometallic Analogue [mer(OC)3(PiPr3)2W(?-pyrazine)W(PiPr3)2(CO)3]+ Of The Creutz-Taube Ion. Similarities And Differences.- Mixed Valence Manganese Carboxylates Of Various Nuclearities.- Spectroscopic Studies Of Spin State And Electron Delocalization In A Binuclear Mixed Valence Fe(II/III) Complex.- Bis(Phthalocyaninato) Lanthanide Sandwich Compounds Exhibiting Mixed Valence Ligands.- The Ruthenium Blues.- Optical And Related Properties Of Metal-Halide Chain Compounds: Bulk And Small Particles.- Dielectric Relaxometry: Manganate (VI)-(VII) In Solid And Solution States.- Electronic Instabilities Of Two-Dimensional Metals, K3Cu8S6 And Rb3Cu8S6.- Chemistry And Properties Of New Examples Of Mixed Valence Compounds, Based On Organic ? Donor Molecules And Polyoxometalate Ions.- Mixed Valency In The Organic-Inorganic Compounds (BEDT-TTF)6Cu2Br6 And (BEDT-TTF)6Cu2Cl2Br4.- Electrochemical Generation Of Mixed Valency Copper Complexes In Solution.- Endor Determination Of Proton Hyperfine Tensors As Local Probes Of The Delocalization Of The Spin Population In The 4 Iron - 4 Sulfur Cubanes.- Theory; Descriptions Of Mixed Valency.- Electron Transfer Mechanisms, From Dimers To Infinite Solids.- Applications: Energy Storage And Molecular Electronics.- Biology: Models And Proteins.