Mononuclear and Dinuclear Ruthenium Complexes of cis- and trans-Thioindigo: Geometrical and Electronic Structure Analyses.

The compounds [Ru(acac)2(L)] (1) and [Ru2(acac)4(μ-L)] (2) with acac- = acetylacetonato and L = thioindigo were characterized crystallographically with a cis-configurated L and O,O'-coordinated metal in 1 and with trans-configurated L and two S,O-coordinated bridged ruthenium centers for 2. The electronic structures of 1 and 2 were confirmed by spectroscopy and density functional theory calculations, suggesting considerable metal-to-ligand electron transfer resulting in the formation of the thioindigo radical anion and oxidized metal(s). UV-Vis-Near-IR and IR (spectro)electrochemistry was used to investigate charged forms 1 n ( n = 1+, 1-) and 2 n ( n = 1+, 1-, 2-), which reveal electron transfer activity of both the metal and the thioindigo ligand as well as sizable orbital mixing. An intense near-IR absorption is observed for 2- at 2180 nm. The remarkable ligand properties of thioindigo are being discussed in connection to related coordination compounds of indigo derivatives such as dehydroindigo and corresponding ("Nindigo") diimines.