VALENCE DISTRIBUTION AND STRUCTURAL DISTORTIONS IN MMX CHAIN COMPOUNDS

We here present an analysis of valence distributions and Peierls-type distortions in one-dimensional halogen-bridged chains MMX. In those sy stems which result from the linking of metal dimers, the phenomenologi cal chain and cluster models show that Peierls distortions can be asso ciated with internal degrees of freedom in dimers and not with the dis placements of bridging halogen atoms. On the other hand, our semiempir ical quantum-chemical band calculations suggest that the role of inter nal Peierls mode in Pt-2(dta)(4)I chains can be played by the twisting distortion of dta ligand. The resulting distribution of valence state s is -M+2-M+3-X-M+3-M+2, in agreement with some experimental data. (C) 1998 American Institute of Physics.