Mixed ligand complexes of osmium(II/III/IV)-2,2' -dipyridylamine synthesis and redox behavior

Department of Chemistry, The University of Burdwan, Burdwan-713 104, India

E-mail : barin_1 @yahoo.co.uk                        Fax : 91-342-530452

Manuscript received 27 August 2001, revised 11 February 2002, accepted 25 April 2002

Eight mixed ligand compounds of osmium(II), -(III), -(IV) of general formula, [Os(dpya)L₂]^z+ [dpya = 2,2'-dipyridylamine; L = 2-(phenylazo)pyridine (L¹), 2-(m-tolylazo)pyridine (L²), 2,2'-bipyridyl (L³), quinolin-8-olate (L⁴) or 2-methylquinolin-8- olate (L⁵); ζ = 1-3] have been prepared, isolated as their perchlorates. The complexes exhibit several spin-allowed and spin-forbidden charge-transfer transitions in the 200-1000 nm region. In MeCN solutions the chelates display Os^IV'-Os^III and Os^III- Os^II couples. The stability of metal oxidation levels is discussed in terms of the electrochemical results and correlated to the π-acceptor properties of these ligands. On the negative side of SCE successive ligand reductions in L¹—L³ complexes are observable.