Publisher Summary This review is concerned with the neglected class of inorganic compounds, which contain ions of the same element in two different formal states of oxidation. Although the number of references cited in our review show that many individual examples of this class have been studied, yet they have very rarely been treated as a class, and there has never before, to our knowledge, been a systematic attempt to classify their properties in terms of their electronic and molecular structures. In the past, systems containing an element in two different states of oxidation have gone by various names, the terms “mixed valence,” nonintegral valence,” “mixed oxidation,” “oscillating valency,” and “controlled valency” being used interchangeably. Actually, none of these is completely accurate or all-embracing, but in our hope to avoid the introduction of yet another definition, we have somewhat arbitrarily adopted the phrase “mixed valence” for the description of these systems. The concept of resonance among various valence bond structures is one of the cornerstones of modern organic chemistry.

Mixed Valence Chemistry-A Survey and Classification

The trans-influence: its measurement and significance

Approximately one-half of all known protein crystal structures in the protein data bank (PDB) contain metal ion cofactors, which play vital roles in charge neutralization, structure, and function.1,2 These proteins range in size from 5000-107 Da with the metal ion corresponding to only on the order of 0.1 wt % of the molecule. Yet, for a wide range of these metalloproteins, the metal ion and its environment are key to the chemistry as these comprise the active site in catalysis. It is the purpose of this review to present the information content of spectroscopic methods, which allow one to focus in on the metalloactive site (Figure 1), define its electronic structure, evaluate the role of the protein in determining geometric and electronic structure, and elucidate the contributions of electronic structure to function. Metalloproteins are simply metal complexes but with remarkably intricate and complex ligands. The metal ion, clusters of metal ions bridged by oxide or sulfide ligands or equatorially chelated by N-heterocyclic ligands (heme, corrin, etc.), are bound to the protein through one or more of the endogenous ligand lone pair donors in Table 1. Note that for most of the donor groups, this requires deprotonation, and the metal ion competition with the proton for the free base lowers the effective pKA by at least several log units from those intrinsic values listed in Table 1. It is important to emphasize that for a number of the ligands in Tables 1 and 2, in particular phenolate, thiolate, oxo and sulfido, and the N-heterocyclic chelates, the metal complex exhibits extremely intense low energy charge transfer (CT) absorption bands, which reflect highly covalent ligand-metal bonds. These make major contributions to the electronic structure of an active site and can be affected by the geometry of the metal site and the orientation of the ligand-metal bond, which in turn can be influenced by the protein matrix. * To whom correspondence should be addressed. † Department of Chemistry, Stanford University. ‡ Stanford Synchrotron Radiation Laboratory, SLAC, Stanford University. 419 Chem. Rev. 2004, 104, 419−458

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Electronic Structures of Metal Sites in Proteins and Models: Contributions to Function in Blue Copper Proteins

A complete Intermediate Neglect of Differential Overlap model suitable for the examination of transition metal complexes is described. The model is characterized by the inclusion of all the one-center exchange terms necessary for rotational invariance and accurate spectroscopic predictions, as well as an accurate description of integrals involving 3d atomic orbitals. The model is within the unrestricted Hartree-Fock formalism, and a method for spin purification is described. Problems with convergence of the self-consistent field are discussed, and a method that has been found successful in aiding the convergence is outlined. The model has been applied to many transition metal systems. In this article the results of calculations on the chlorides of Fe, Co and Cu are described. The results of these calculations are compared with experiment, and with the results of calculations by other methods.

An intermediate neglect of differential overlap theory for transition metal complexes: Fe, Co and Cu chlorides

Coordination polymers are currently one of the hottest topics in Inorganic and Supramolecular Chemistry. This critical review summarizes the current state-of-the-art on electrical conductive coordination polymers (CPs), also named metal–organic frameworks (MOFs). The data were collected following two sort criteria of the CPs structure: dimensionality and bridging ligands (151 references).

Electrical conductive coordination polymers

Crystal structures of the green and yellow thermochromic modifications of bis(N-Methylphenethylammonium) tetrachlorocuprate (II). Discrete square-planar and flattened tetrahedral tetrachlorocuprate(2-)anions

Diethylenetriamine complexes of platinum(II) halides

Crystal and molecular structure of bis[(+)-N,.alpha.-dimethylphenethylammonium] tetrachlorocuprate(II). Relation between the electronic spectrum and the distortion of the tetrachlorocuprate chromophore from tetrahedral symmetry

George W. Watt

Papers

Crystal structures of the green and yellow thermochromic modifications of bis(N-Methylphenethylammonium) tetrachlorocuprate (II). Discrete square-planar and flattened tetrahedral tetrachlorocuprate(2-)anions

Diethylenetriamine complexes of platinum(II) halides

Crystal and molecular structure of bis[(+)-N,.alpha.-dimethylphenethylammonium] tetrachlorocuprate(II). Relation between the electronic spectrum and the distortion of the tetrachlorocuprate chromophore from tetrahedral symmetry

Concerning the Status of Bis(cyclopentadienyl)titanium

The Infrared Spectra and Structure of Bis(ethylenediamine)palladium(II) and -platinum(II) Halides