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)nUIV.Ci6IrIV ]2+ binuclear intermediate, followed by a slower stage which was explained as the transfer of electrons from UIV to IrIV following the loss of one or two protons from water molecules of (H2O)nUIV. A tentative reaction mechanism consistent with the kinetic results is discussed. (author)