Electronic and resonance-Raman spectra of the linear-chain mixed-valence platinum complexes {[Pt(en)2][Pt(en)2X2]}3[CuX4]4[X = Cl (1) or Br (2)] and [Pt(pn)2][Pt(pn) Br2][Cu3Br5]2(3)(en = ethane-1,2-diamine and pn = propane-1,2-diamine)

Abstract

Electronic, infrared, and resonance-Raman (r.r.) spectra of the title complexes have been recorded, as well as single-crystal polarised specular-reflectance spectra of complex (2) in the region 5 000–25 000 cm^–1. The r.r. spectra have been obtained with exciting lines whose wavenumbers fall within contours of the intense, axially polarised, intervalence bands observed in the 15 000–20 000 cm^–1 region of the transmission and specular-reflectance spectra of each complex. The r.r. spectra are characterised by the appearance of an intense progression, v₁ν₁(reaching at most v₁=17) where ν₁ is the symmetric (X–Pt^IV–X) stretching mode. Weak subsidiary progressions, ν_n+v₁ν₁, also appear in the spectra, where ν_n is another Raman-active mode. The spectroscopic constants ω₁ and x₁₁ are calculated. The excitation profiles of the Stokes ν₁ band and additionally, in the case of the two bromo-complexes, of the Stokes 2ν₁, 3ν₁, and anti-Stokes ν₁ bands, have been measured, and all found to reach maxima on the low-energy side of the electronic band maximum. The present results are compared with previous ones on related linear-chain complexes.