Electronic and vibrational studies of mixed-valence complexes. The resonance raman spectra of the bromine-bridged platinum complexes [Pt(LL) 2][Pt(LL) 2Br 2] Br 4, where L L = 1,2-diaminoethane, -propane, -butane, and -pentane

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Electronic, infrared and resonance Raman (RR) spectra of the mixed-valence, bromine-bridged platinum complexes [Pt(LL) 2][Pt(LL) 2Br 2]Br 4, where LL = 1,2-diaminoethane, -propane, -butane, or -pentane, have been recorded. The electronic spectra are characterised by strong, broad bands in the visible region, attributable to Pt II → Pt IV charge transfer. The RR spectra, obtained on resonance with this band, display long overtone progressions, v 1v 1, in the totally symmetric chain mode, v(BrPt IVBr), reaching v 1 = 11, 7, 8, an d8 for the 1,2-diaminoethane, -propane, -butane, and -pentane complexes, respectively. The harmonic wavenumber, ω 1, and the anharmonicity, x 11, are both independent of the mass of the amine, the average values being ω 1 = 171.2 ± 0.6 cm −1, and x 11 = −0.35 ± 0.09 cm −1; this result demonstrates the highly one-dimensional nature of the complexes. The excitation profiles of the v 1, 2v 1 and 3v 1 bands all maximise on the low wavenumber side of the intervalence transition maximum.