Hydration and water-exchange mechanism of the UO2 2+ ion revisited: the validity of the "n + 1" model.
Hydration and water-exchange mechanism of the UO2(2+) ion was studied by the B3LYP calculations. Relative Gibbs energies in aqueous phase of the 4-, 5-, and 6-fold uranyl(VI) hydrates were compared. A model with a complete first hydration shell and one water in the second shell was used (which is called "n + 1" model) to compare the energy of the UO2(2+) ion with different hydration numbers. The n + 1 model tends to overestimate the overall stability of the complex, and this type of model should be carefully used for the determination of the coordination number or the coordination mode such as unidentate or bidentate. A stable 5-fold uranyl(VI) hydrate goes through a very rapid water-exchange process via an associative (A-) mechanism keeping the 5-fold uranyl(VI) the dominant species.
Tsushima
Satoru
S
Forschungszentrum Dresden-Rossendorf (FZD), Institute of Radiochemistry, P.O. Box 510119, 01314 Dresden, Germany. S.Tsushima@fzd.de