Excitation wavenumber dependence of the symmetric chain-stretching mode of linear-chain mixed-valence platinum complexes

Abstract

The wavenumber, ν₁, of the symmetric chain-stretching mode of linear-chain halogen(X)-bridged mixed-valence complexes of platinum increases as the wavenumber of the excitation line (ν₀) increases, whereas those of equatorial modes do not. For any set of complexes the wavenumber change, ν₁(λ₀= short wavelength)–ν₁(λ₀= long wavelength), increases in the order Cl < Br < I and is largest for those complexes in which the Pt^II⋯ Pt^IV separation is least and for which the bond-length ratio r(Pt^IV–X)/r(Pt^II–X) is nearest to unity. This suggests that the wavenumber dispersion of v₁ with v₀ depends on the extent of valence delocalisation along the chain.