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 {[Ru^II(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⁺, Ru₂^II,II, were oxidized by 1 equivalent in solution leading to the mixed valence Ru₂^II,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 H_ab 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 Ru₂^III,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 Ru₂^II,II and ligand to metal charge transfer (LMCT) type for Ru₂^III,II and Ru₂^III,III.