Mixed ligand complexes of osmium(II)-2,2′-bipyridine: synthesis, spectral characterization and electrochemical properties of bis-chelated-arylazoimidazole-bipyridine-osmium(II) and X-ray crystal structure of [(2,2′-bipyridine)-bis-{1-methyl-2-(p-tolylazo)

Reaction of ctc-OsBr2(RaaiR′)2 [RaaiR′=1-alkyl-2-(arylazo)imidazole, p-R-C6H4-NN-C3H2-NN-1-R′, where R=H (a), Me (b), Cl (c) and R′=Me (2), Et (3) and CH2Ph (4)] with 2,2′-bipyridine (bpy) in presence of AgNO3 in EtOH followed by the addition of NH4PF6 afforded a mixed ligand complex [Os(bpy)(RaaiR′)2](PF6)2. The structure of the complex, in one case [Os(bpy)(MeaaiMe)2](PF6)2 · 4H2O, has been confirmed by X-ray crystallography. The complexes are diamagnetic (low spin d6, s=0) and they show intense MLCT transition in the visible region (480–525 nm) and a weak transition at longer wavelength (>850 nm) in CH3CN solution. Cyclic voltammetry of the complexes show two metal oxidation, Os(II)/Os(III) at 0.72–0.76 V and Os(III)/Os(IV) at 1.34–1.42 V and three successive ligand reductions.