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

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 [U^v(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.