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A group of stable new ruthenium (II) mixed tris-chelated complexes of the type [Ru(bpy)(2)(L)]ClO4 . 2H(2)O, [bpy:2,2'-bipyridine; L:anionic form of KSSCOR, R = Me, Et, (n)pr, (n)Bu] have been prepared by the reaction of Ru(bpy)(2)CO3 with KSSCOR in methanol. The complexes are essentially diamagnetic and behave as 1:1 electrolytes in CH3CN. All the complexes show metal to ligand charge transfer transitions in the visible region (495-450 nm). The complexes do not exhibit any emission spectra at room temperature. The geometry of the complexes has been assessed by high-resolution H-1 NMR spectroscopy. Reductions of coordinated bpy units are observed in the range -1.5 and -1.8 V, respectively. All the complexes exhibit one reversible ruthenium (II)-ruthenium(III) oxidation couple near 0.7 V (versus SCE) in acetonitrile solution at platinum electrode. Coulometric oxidation of [Ru-II(bpy)(2)(L)](+) at 0.9 V.(vs. SCE) as well as chemical oxidation by Ce(IV) in 0.1M aqueous HClO4 produces unstable green coloured ruthenium(III) congener of [Ru-II(bpy)(2)(L)(+) i.e. [Ru-III(bpy)(2)(L)](+2). The presence of trivalent ruthenium in the oxidized solution is evidenced by the rhombic EPR spectrum with g values (g(1) = 2.720, g(2) = 2.370 and g(3) = 1.700).

Mixed ligand phenolate Schiff base complexes of ruthenium (II) of the types [Ru(pap)(2)L]ClO4, [pap = 2-(phenylazo) pyridine; L = deprotonated form of HL ligand, HO-C6H4-CH=N-C6H4-(R), where R = H, Me, OMe, Cl, NO2] and [Ru(bpy)(2)L(2)]ClO4H2O (where bpy = 2,2'-bipyridine) have been synthesised and characterised. The complexes are diamagnetic and in acetonitrile solution they behave as 1:1 electrolyte. All the complexes show strong MLCT transitions in the visible region 400-800 nm. The redox properties of all these complexes have also been studied.