Electronic, Raman, and resonance Raman spectra of mixed-valence anion-chain complexes of platinum

Abstract

Electronic, Raman, and resonance Raman (r.R.) spectra of the mixed-valence anion-chain complexes M₂[Pt(L)X₃][Pt(L)X₅](M = K or NH₄, L = NH, or pyridine, and X = Cl, Br, or I) have been recorded at ca. 80 K. The electronic spectra are characterised by strong bands in the visible region, attributable to the intervalence transition Pt^IVâ†�Pt^II. The r.R. spectra display long overtone progressions (v₁ν₁), νv₁ being the totally symmetric axial breathing mode, ν_sym.(X–Pt^IV–X)_ax., together with combination band progressions v₁ν₁+ν₂ and v₁ν₁+ν₃, where ν₂ and ν₃ are the totally symmetric stretching modes of the equatorial halogen atoms, ν_sym.(Pt–X)_eq.. The excitation profiles of the fundamentals, ν₁, ν₂, ν₃, and in some cases of 2ν₁, have been measured and all found to maximise on the low-energy side of the intervalence band maximum. The r.R. results indicate a substantial change in the Pt–X_ax. bond length on excitation from the ground to the intervalence state for each complex, together with other smaller changes in the Pt–X_eq. bond lengths.