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

A series of RuN6 dinuclear Ru-Hbpp complexes (Hbpp is the dinucleating tetraaza ligand 3,5-bis(pyridyl)pyrazole) of general formula {[Ru-II(R-2-trpy)(MeCN)](2)(mu-R-1-bpp)}3(+), 10(3+)-14(3+), (R-1 = H, Me, or NO2. and R-2 = 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 10(3+)-14(3+), Ru-2(II,II), were oxidized by 1 equiv in solution, leading to the mixed valence Ru-2(II,III) complexes 10(4+)-14(4+) 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 the 10(3+)-14(3+) led to the formation of EPR silent Ru-2(II,III) complexes 10(5+)-14(5+), 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 Ru-2(II,II) and ligand to,m. metal charge transfer (LMCT) type for Ru-2(III,II) and Ru-2(III,III).