Electronic, infrared, and resonance-Raman spectra of linear-chain mixed-valence complexes of platinum with 1,2-diaminopropane

Abstract

The electronic, infrared, and resonance-Raman spectra of the linear-chain complexes [Pt(pn)₂][Pt(pn)₂X₂]Y₄(X = Cl, Br, or I; Y = ClO₄ and X = Br; Y = BF₄, where pn = 1,2-diaminopropane) are reported. The electronic spectrum of each complex is characterised by an intense, broad, intervalence band (Pt^IVâ†� Pt^II) in the visible region, the wavenumber maximum of which depends on particle size. Irradiation within the intervalence band contour leads to strong intensification of the Raman band attributed to the totally symmetric stretching mode ν₁, ν_sym(X–Pt^IV–X) and its overtones. The excitation profiles (e.p.) of ν₁ and its overtones are also sensitive to particle size, and maximise on the low-energy side of the intervalence band maximum in each case. The e.p. maxima and the intervalence band maxima both increase in wavenumber as the particle size is reduced. The wavenumbers of ν₁ and its overtones are independent of particle size, but do depend slightly on the exciting line used to gather data. This dispersion of the ν₁ mode is related to the extent of valence delocalisation along the ⋯–X–Pt^IV–X ⋯ Pt^II⋯ chains.