RESONANCE RAMAN AND FAR-INFRARED STUDIES OF ISOTOPICALLY DISORDERED AND MIXED-HALIDE HALOGEN-BRIDGED PLATINUM CHAIN SOLIDS

The MX chain solids [Pt(en)2][Pt(en)2X2](ClO4)4, (en = C2H8N2 and X = Cl, Br), referred to as ''PtX,'' are used to explore some of the surpr ising spectral consequences of disorder in 1-D systems, first for pure PtCl, where the disorder arises from randomly distributed Cl isotopes , then for the more drastic case of the mixed-halide materials PtCl1-x Brx. Lattice dynamics and Peierls-Hubbard modelling are used to analyz e the observed spectral behavior. In both cases, the complex structure seen in the Raman and IR spectra is found to arise from strongly loca lized vibrational modes residing on chain segments, defined by sequenc es of Cl isotopes for PtCl, and by sequences of Cl and Br for PtCl1-xB rx.