Neutral chain bromide- and iodide-bridged platinum(II,IV) complexes of 1,2-diaminoethane and thiocyanate: synthesis, electronic, infrared, Raman, and resonance-Raman studies

Abstract

The complexes Pt(en)(SCN)₂X, en = 1,2-diaminoethane, X = Br or I, have been synthesised and, on the basis of a study of their electronic, i.r., and resonance-Raman spectra, established to be linear-chain, halogen-bridged complexes, [Pt(en)(SCN)₂][Pt(en)(SCN)₂X₂]. The electronic spectra are characterised by broad, intense bands (maxima at ca. 17 800 cm^–1 for X = Br and at < 13 000 cm^–1 for X = I). The i.r. spectra are near superpositions of those of the constituent complexes, the band shifts on complex formation being greater for the iodide-bridged complex. The resonance-Raman spectra are dominated by long overtone progressions in ν₁, the Raman-active, symmetric (X–Pt^IV–X) stretch, reaching 7ν₁ for X = Br or I. Subsidiary progressions v₁ν₁+ν_n are observed for X = Br, where ν_n is identified as ν(Pt–S)_eq. The form of the resonance-Raman spectra, ν₁ excitation profiles, and ν₁ wavenumber dependence on the wavenumber of the exciting line, ν₀, are discussed in terms of unresolved components of ν₁ and of their relative intensity dependence on temperature and ν₀.