Electronic and Resonance Raman Spectra of [Au2(CS3)2]2-. Spectroscopic Properties of a “Short” Au(I)-Au(I) Bond

The anion [Au2(CS3)2]2- has an unusually short Au−Au distance (2.80 A) for a binuclear Au(I) complex. We report detailed Raman studies of the nBu4N+ salt of this complex, including FT-Raman of the solid and UV/vis resonance Raman of dimethyl sulfoxide solutions. All five totally symmetric vibrations of the anion have been located and assigned. A band at Δν = 125 cm-1 is assigned to ν(Au2). The visible-region electronic absorption bands (384 (e 30 680) and 472 nm (e 610 M-1 cm-1)) are attributable to CS32- localized transitions, as confirmed by the dominance of νsym(C−Sexo) (Δν = 951 cm-1) in RR spectra measured in this region. An absorption band at 314 nm (22 250 M-1 cm-1) is assigned as the metal−metal 1(dσ* → pσ) transition, largely because νsym(C−Sexo) is not strongly enhanced in RR involving this band. Observation of the expected strong resonance enhancement of ν(Au2) was precluded as a result of masking by intense solvent Rayleigh scattering in the UV.