Vibrational and electronic spectra of [Pt2(SO4)]2- complexes

Abstract

The vibrational and electronic spectra of axially ligated sulfate-bridged binuclear platinum complexes ([Pt2(SO4)4L2]n-: L = OH2, DMSO, n = 2; L = Cl, Br, n = 4) have been studied. Raman spectra acquired with near-UV excitation show bands assigned to Pt-O(sulfate) stretching (300-350-cm-1 region) for all complexes, while bands assigned to Pt-Pt and Pt-L stretching are seen for complexes (L = Cl, Br) that display preresonance Raman scattering within intense near-UV absorption bands assigned to the σ(L) → σ*(Pt2) electronic transition. Weaker electronic absorptions are assigned as metal-metal 1(σ→σ*) (near 220 nm for L = OH2, Cl) and dπ → dσ*(Pt2) (350-500 nm). Single-crystal polarized absorption spectra (L = OH2, DMSO) show that the weak absorption system in the 350-500-nm region consists of three x,y-polarized (metal-metal axis) bands and an x,y-polarized band. The L = OH2, Cl complexes show weak emission bands in the 695-750-nm region when excited at 77 K with near-UV light. These emission bands are similar to those observed for [Pt2(HPO4)4L2]n- (L = OH2, n = 2; L = Cl, n = 4) complexes. The emission lifetimes for the sulfate-bridged complexes (450 ± 50 ns, L = OH2; 290 ± 20 ns, L = Cl) are much shorter, and the emission intensities are much weaker, than the corresponding properties of the phosphate-bridged complexes. © 1991 American Chemical Society.