Syntheses, crystal structures and spectroelectrochemical studies of two isomeric binuclear osmium carbonyl compounds [{Os(CO)2Ph}2{m-h2-SC(NNPh)2}2]

Treatment of (diphenylthiocarbazono)phenylmercury [PhHg{SC(NNPh)2}] with the triosmium cluster [Os3(CO)10(NCMe)2] produced two structural isomers 1a and 1b of formulae [{Os(CO)2Ph}2{μ-η2-SC(NNPh)2}2] in 35 and 20% yield, respectively. The complexes were fully characterised by IR, 1H-NMR, mass spectroscopies and X-ray crystallography. The isomers 1a and 1b show no significant metal–metal interaction and are different in the arrangement of the organic ligand. Complex 1a was found to undergo a complete conversion to 1b in the presence of excess reducing agent Co(Cp)2. The electrochemical and spectroelectrochemical (UV–vis) properties of these two complexes are described