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

Abstract

According to previous electronic absorption, resonance Raman and DFT studies the lowest-energy electronic transition of the RuII and OsII complexes trans,cis-[M(SnR3)2(CO)2(α-diimine)] (α-diimine = bpy, etc.) has a σ(Sn–M–Sn) → π*(α-diimine) or sigma-bond-to-ligand charge-transfer (SBLCT) character. Nanosecond time-resolved step-scan IR (s2-TRIR) spectra of a series of these complexes are reported which indicate that the initial SBLCT excitation is followed by a redistribution of the electron density if this transition has an appreciable charge transfer character. This effect is virtually the same for the Ru and Os compounds, but different for the SnMe3 and SnPh3 complexes. s2-TRIR spectra of [Os(SnPh3)2(CO)2(dmb)] showed the occurrence of an infrared rigidochromic effect in a low-temperature glass.