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Synthesis, Structure, and Electronic Properties of RuN6 Dinuclear Ru-Hbpp Complexes

Roeser, S.; Ertem, M. Z.; Cady, C.; Lomoth, R.; Benet-Buchholz, J.; Hammarström, L.; Cramer, C. J.; Llobet, A.
Inorg. Chem. 2012, 51, 320 (doi:10.1021/ic201668r).

A series of RuN6 dinuclear Ru-Hbpp complexes (Hbpp is the dinucleating tetraaza ligand 3,5-bis(pyridyl)pyrazole) of general formula {[RuII(R2-trpy)(MeCN)]2(μ-R1-bpp)}3+, 103+-143+, (R1 = H, Me or NO2 and R2 = H, Me, MeO; see Scheme 1) has been prepared from their Cl- or AcO- bridged precursors. The complexes have been characterized by UV-vis, NMR, CV and some by X-ray. Complexes 103+-143+, Ru2II,II, were oxidized by 1 equivalent in solution leading to the mixed valence Ru2II,III complexes 104+-144+ containing one unpaired electron and were characterized by EPR and UV-vis-near-IR which showed metal-centered spin and the presence of low-energy IVCT bands. The Hab parameter indicates a relatively strong electronic coupling between the two ruthenium centers (Class II). Further two electron oxidation in solution of 103+-143+ led to the formation of EPR silent Ru2III,III complexes 105+-145+, that were further characterized by UV-vis-NIR. TD-DFT calculations are employed to assign the nature of the UV-vis transitions for the complexes in the various oxidation states, which are of metal to ligand charge transfer (MLCT) type for Ru2II,II and ligand to metal charge transfer (LMCT) type for Ru2III,II and Ru2III,III.