| Abstract
| - Hydration and water-exchange mechanism of the UO22+ ion was studied by the B3LYP calculations. RelativeGibbs energies in aqueous phase of the 4-, 5-, and 6-fold uranyl(VI) hydrates were compared. A model witha 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 UO22+ ion with different hydration numbers. The n + 1 model tends tooverestimate the overall stability of the complex, and this type of model should be carefully used for thedetermination of the coordination number or the coordination mode such as unidentate or bidentate. A stable5-fold uranyl(VI) hydrate goes through a very rapid water-exchange process via an associative (A-) mechanismkeeping the 5-fold uranyl(VI) the dominant species.
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