Structural and kinetic studies on uranyl(V) carbonate complex using 13C NMR spectroscopy

We have measured C-13 NMR spectra of uranyl(V) carbonate complex in D2O solution containing 1.003 M Na-2 (CO3)-C-13 at various temperatures. Two singlet signals corresponding to free and coordinated CO32- 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 [(UO2)-O-V(CO3)(3)](5-). Furthermore, kinetic analyses of the exchange reaction of free and coordinated CO32- in [(UO2)-O-V(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 CO32- exchange reaction in [(UO2)-O-V(CO3)(3)](5-) were evaluated as 1.13 x 10(3) s(-1) and Delta H-not equal = 62.0 +/- 0.7 KJ(.)mol(-1), Delta S-not equal = 22 +/- 3 J(.)mol(-1.)K(-1), respectively. We suggest that the exchange follows a dissociative mechanism as in the corresponding [(UO2)-O-VI(CO3)(3)](4-) complex.