Synthesis, characterization and redox properties of ruthenium(ll) dithiocarbonato complexes having 2,2'-bipyridine coligands

Abstract

A group of stable new ruthenium (II) mixed tris-chelated complexes of the type [Ru(bpy)₂(L)]CIO₄.2H₂O, [bpy:2,2'-bipyridine; L:anionic form of KSSCOR, R=Me, Et, "pr, <i>"</i>Bu] have been prepared by the reaction of Ru(bpy)₂CO₃ 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 ¹H 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(lll) oxidation couple near 0.7 V (versus SCE) in acetonitrile solution at platinum electrode. Coulometric oxidation of [Ru^ll(bpy)₂(L)]⁺ at 0.9 V (vs. SCE) as well as-chemical oxidation by Ce(IV) in 0.1<i>M </i> aqueous HCIO₄ 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 ‘<i>g </i> values (<i>g</i>₁ =2.720, <i>g</i>₂=2.370 and <i>g</i>₃= 1.700).