Electrochemical and spectroelectrochemical studies on UO(2)(saloph)L (saloph = N,N'-disalicylidene-o-phenylenediaminate, L=dimethyl sulfoxide or N,N-dimethylformamide)

To examine properties of pentavalent uranium, U(V), we have carried out electrochemical and spectroelectrochemical studies on UO(2)(saloph)L [saloph = N,N'-disalicylidene-o-phenylenediaminate, L = dimethyl sulfoxide (DMSO) or N,N-dimethylformamide (DMF)]. The electrochemical reactions of UO(2)(saloph)L complexes in L were found to occur quasireversibly. The reduction processes of UO(2)(saloph)L complexes were followed spectroelectrochemically by using an optical transparent thin layer electrode cell. It was found that the absorption spectra measured at the applied potentials from 0 to -1.650 V versus ferrocene/ferrocenium ion redox couple (Fc/Fc(+)) for UO(2)(saloph)DMSO in DMSO have clear isosbestic points and that the evaluated electron stoichiometry equals 1.08. These results indicate that the reduction product of UO(2)(saloph)DMSO is [U(V)O(2)(saloph)DMSO](-), which is considerably stable in DMSO. Furthermore, it was clarified that the absorption spectrum of the [U(V)O(2)(saloph)DMSO](-) complex has a very small molar absorptivity in the visible region and characteristic absorption bands due to the 5f(1) orbital at around 750 and 900 nm. For UO(2)(saloph)DMF in DMF, the clear isosbestic points were not observed in the similar spectral changes. It is proposed that the UO(2)(saloph)DMF complex is reduced to [U(V)O(2)(saloph)DMF](-) accompanied by the dissociation of DMF as a successive reaction. The formal redox potentials of UO(2)(saloph)L in L (E(0), vs Fc/Fc(+)) for U(VI)/U(V) couple were determined to be -1.550 V for L = DMSO and -1.626 V for L = DMF.