Kinetics of reaction of uranium(IV) and hexachloroiridate(IV) in acid perchlorate solutions. Evidence for a binuclear intermediate

Abstract

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 k₁Å 6.86 × 10³ dm³ mol^–1 s^–1, decomposition k_–1= 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.