ELECTROCHEMISTRY IN LIQUID SO2 .11. OXIDATION OF NI(BPY)3(2+) AND SPECTROSCOPY AND ISOLATION OF PRODUCTS

The electrochemical oxidations of Ni(bpy)3(2+) (bpy = 2,2'-bipyridine) in 0.1 M tetrabutylammonium hexafluoroarsenate solution in liquid sulfur dioxide was studied by cyclic voltammetry and spectroscopic (UV-vis and ESR) techniques. Within the accessible potential range four successive oxidations could be observed. The first one-electron reversible oxidation, at about +1.3 V vs a silver quasireference electrode (AgQRE), corresponds to the oxidation of the metal center. The second oxidation, at about +2.0 V vs AgQRE, produces Ni(bpy)3(4+), which exhibits thermochromic properties. The thermochromism of the Ni(bpy)34+ is attributed to the dependence of the degree of charge transfer interactions between the Ni(IV) center and bpy ligands on temperature. The third, reversible oxidation, at +3.2 V, is attributed to the oxidation of a coordinated bpy, and the fourth, totally irreversible oxidation at, +3.5 V, is a multielectron process. The procedure of separation and purification of a new very strong, solid oxidant, Ni(bpy)3(AsF6)4 (E-degrees = 2.5 V vs SCE), is presented.