Structural Study of Bromo-Bridged One-Dimensional NiII–NiIVMixed Valence Complexes by Means of Exafs

A vibronic approach to the band-filling and temperature-dependent metal-insulator transition

A model of vibronic origin is used to investigate the important issue of metal-insulator transition in low-dimensional materials. For zero temperature, the stability of the single-band model chain is controlled by the competition between the internal electron-phonon coupling and the nearest-neighbor hopping integral. Assuming one particular deformation mode, one can analytically derive an instability criterion in which the band filling is explicitly included. The carrier doping directly controls the stability of a one-dimensional chain. For a half-filled band, the Peierls instability is recovered. For finite temperatures, a similar criterion is derived and can be used to investigate the metal-insulator transition temperatures.

Halogen-Bridged Mixed-Valence Linear-Chain Complexes: Molecular Orbital Model of Electron Localization

A simple tight-binding model is used to study electronic distributions and Peierls distortions in a series of mixed-valence linear-chain complexes [M(II)(LL)(2)][M(IV)(LL)(2)X(2)] (M = Ni, Pd, Pt; X = Cl, Br, I; LL = 1,2-diaminoethane, 1,3-diaminopropane). The calculated values of Peierls distortions for complexes with known structure are in good agreement with the experimental data. For the whole series, the model is employed as a qualitative tool to analyze structural and electronic properties. It is shown that charge disproportionation occurs in the related dimers. Thus, our quantum chemical calculations as well as previous phenomenological approaches indicate that, in metal-halogen chains, one deals with the interplay of local and cooperative effects.