Synthesis, crystal structure and redox properties of μ-oxo-bis(μ-acetato)-diruthenium(III) complexes having 2,2'-bipyridine and imidazole bases as terminal ligands

Three diruthenium(III) complexes, [{Ru(bipy)L}2(μ-O)(μ-O2CMe)2][ClO4]2, have been prepared and characterized (L = imidazole, 1- or 4-methylimidazole; bipy = 2,2'-bipyridine). The crystal structure of the 1-methylimidazole complex [Ru2O(O2CMe)2(bipy)2(1-mim)2][ClO4]2·H 2O·MeOH has been determined. The complex has a Ru2(μ-O)(μ-O2CMe)22+ core with terminal unidentate 1-mim and bidentate chelating bipy ligands. The imidazole is trans to the oxide ligand. The Ru Ru distance and Ru-O-Ru angle are 3.285(2)Å and 121.5(3)°. The 1H NMR spectra of the complexes are consistent with this crystal structure. The complexes show an intense charge-transfer band near 600 nm. They are redox active and display reversible one-electron oxidation and reduction processes. On addition of weak proton-donor imidazole bases the complexes undergo a one-step two-electron reduction process RuIIIRuIII-RuIIRuII along with the RuIIIRuIII-RuIIIRuIV oxidation couple