Electrochemical behaviour of tris (2,2′-bipyridine) osmium(II) complex in dimethylformamide

Abstract

The electrochemical behaviour of Os(bpy) 3 2+ (bpy=2,2′-bipyridine) has been investigated in N,N-dimethylformamide by utilizing predominantly the techniques of polarography and cyclic voltammetry. The study has been carried out at different temperatures in the range −20 to +30° C. The number of reduction waves observed depends markedly on temperature. For intermediate temperatures, the complex exhibits six reduction waves, the maximum number of waves observed as a function of temperature. The first three reduction processes, corresponding to the first three reduction waves, are one-electron, diffusion-controlled reversible processes in all conditions. Conversely, process four is consistent with one-electron reversible transfer only at the lowest temperature. In fact, for higher temperatures the liberation of bpy, preferentially as a radical anion rather than a neutral molecule, occurs. In the latter case, the liberated neutral bpy molecule can be reduced by one-electron transfer. Process five is due to the reduction of species formed by chemical reaction in the preceding electrode process, i.e. the bpy radical anion and Os(bpy) 2 1−. Process six is consistent with the addition of five electrons to the starting complex, followed by the liberation and successive reduction of the bpy radical anion.