title: Structural and kinetic studies on uranyl(V) carbonate complex using 13C NMR spectroscopy.
abstract: We have measured 13C NMR spectra of uranyl(V) carbonate complex in D2O solution containing 1.003 M Na2(13)CO3 at various temperatures. Two singlet signals corresponding to free and coordinated CO3(2-) were observed at 169.13 and 106.70 ppm, respectively. From the peak area ratio, the structure of the uranyl(V) carbonate complex was determined as [U(V)O2(CO3)3]5-. Furthermore, kinetic analyses of the exchange reaction of free and coordinated CO3(2-) in [U(V)O2(CO3)3]5- were carried out using 13C NMR line-broadening. As a result, the first-order rate constant at 298 K and the activation parameters for CO3(2-) exchange reaction in [U(V)O2(CO3)3]5- were evaluated as 1.13 x 10(3) s(-1) and deltaH(double dagger) = 62.0 +/- 0.7 kJ x mol(-1), deltaS(double dagger) = 22 +/- 3 J x mol(-1) x K(-1), respectively. We suggest that the exchange follows a dissociative mechanism as in the corresponding [U(VI)O2(CO3)3]4- complex.
authors.affiliation: Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8550, Japan.
authors.forename: Koichiro
authors.initials: K
authors.lastname: Mizuoka
authors.forename: Ingmar
authors.initials: I
authors.lastname: Grenthe
authors.forename: Yasuhisa
authors.initials: Y
authors.lastname: Ikeda