Coordination environment of aqueous uranyl(VI) ion

Water dissociation from [UO2(OH2)5]2+ is studied with Car-Parrinello molecular dynamics simulations (using the BLYP density functional) in the gas phase and in aqueous solution. Free energies, ΔA, are estimated from pointwise thermodynamic integration using one U-O(H2) distance as a reaction coordinate. While an isomeric, four-coordinate complex, [UO2(OH2)4]2+·H2O, is more stable than the five-coordinate reactant in the gas phase (ΔA = -2.2 kcal/mol), the former is strongly disfavored in water (ΔA = +8.7 kcal/mol). Copyright © 2005 American Chemical Society.