A time-resolved infrared spectroscopic study of [M(SnR3)(2)(CO)(2)(alpha-diimine)] (M = Ru, Os; R = Ph, Me): evidence of charge redistribution in thelowest-excited state

According to previous electronic absorption, resonance Raman and DFT studie s the lowest-energy electronic transition of the Ru-II and Os-II complexes trans.cis-[M(SnR3)(2)(CO)(2)(alpha -diimine)] (alpha -diimine = bpy, etc.) has a sigma (Sn-M-Sn) --> pi*(alpha -diimine) or sigma-bond-to-ligand charg e-transfer (SBLCT) character. Nanosecond time-resolved step-scan IR (s(2)-T RIR) spectra of a series of these complexes are reported which indicate tha t the initial SBLCT excitation is followed by a redistribution of the elect ron density if this transition has an appreciable charge transfer character . This effect is virtually the same for the Ru and Os compounds, but differ ent for the SnMe3 and SnPh3 complexes. s(2)-TRIR spectra of [Os(SnPh3)(2)(C O)(2)(dmb)] showed the occurrence of an infrared rigidochromic effect in a low-temperature glass.