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 PtIVâ†�PtII. The r.R. spectra display long overtone progressions (v1ν1), νv1 being the totally symmetric axial breathing mode, νsym.(X–PtIV–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, νsym.(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–Xax. bond length on excitation from the ground to the intervalence state for each complex, together with other smaller changes in the Pt–Xeq. bond lengths.