KINETICS OF REACTION OF URANIUM(IV) AND HEXACHLOROIRIDATE(IV) IN ACID PERCHLORATE SOLUTIONS - EVIDENCE FOR A BINUCLEAR INTERMEDIATE

The kinetics of oxidation of uranium(IV) with hexachloroiridate(IV) in aqueous perchlorate media at a constant ionic strength of 1.0 mol dm-3 has been reinvestigated using stopped-flow and conventional spectrophotometric techniques. There are two distinct stages in the reaction: the initial stage is fast and interpreted as being the formation of a [(H2O)nU(IV).Cl6Ir(IV)\2+ binuclear intermediate (rate of formation k(l 6.86 x 10(3) dm3 mol-1 s-1, decomposition k(-l) = 3.91 s-1), followed by a slower stage which was explained as the transfer of electrons from U(IV) to Ir(IV) following the loss of one or two protons from water molecules of (H2O)nU(IV). A tentative reaction mechanism consistent with the kinetic results is discussed.