Electrochemical Studies on [U(dmso)9]4+ and [UO2(dmso)5]2+ (dmso = dimethyl sulfoxide) Complexes in DMSO

Abstract

Electrochemical studies on [U(dmso)9]4+ and [UO2(dmso)5]2+ complexes in DMSO containing tetrabutylammonium perchlorate(TBAP) as supporting electrolyte have been carried out by using cyclic voltammetry(CV). A three electrode system was utilized, i.e., Pt working, Ag/Ag+ in TBAP/CH3CN reference, and Pt auxiliary electrodes. A ferrocene/ferrocenium (Fc/Fc+) couple was used as a reference redox system. Measurements of CV were carried out in the range of -0.025 to -2.025 V and -0.025 to -1.175 V for [U(dmso)9]4+ and [UO2(dmso)5]2+ complexes, respectively It was found that the [UO2(dmso)5]2+ complex is reduced quasi-reversibly to U(V) at around -1.0 V, and that the [U(dmso)9]4+ complex is reduced quasi-reversibly to U(III) at around -0.93 V and the resulting U(III) species is further reduced to U(0) irreversibly at around -1.7 V. The formal redox potentials(vs. Fc/Fc+) for U(VI)/U(V) and U(IV)/U(III) couples were determined to be -0.970 and -0.901 V, respectively Furthermore, in order to examine whether the [U(dmso)9]4+ complex is oxidized to U(V), the cyclic voltammogram was measured in the range of -0.025 to +0.975 V at the scan rate of 0.05V/s. Any anodic and cathodic peaks were not observed within the potential window. This indicates that the [U(dmso)9]4+ complex is not oxidized to [Uv(dmso)9]5+. These results suggest that the U(V) species in non-aqueous solvents can be present more stably as yl-type(UO2+) than as U5+ type.