Covalency hinders AnO2(H2O)+ → AnO(OH)2+ isomerisation (An = Pa–Pu)

Abstract

The enthalpies of the reactions AnO₂⁺ → AnO⁺ + O and AnO₂⁺ + H₂O → AnO₂(H₂O)⁺, and those of the isomerisation of the latter to AnO(OH)₂⁺, have been calculated for An = Pa–Pu. The data match previous experimental and computational values very closely, and the computed enthalpy for the isomerisation of PaO₂(H₂O)⁺ to PaO(OH)₂⁺, requested by the authors of Inorg. Chem., 2015, 54, 7474, is found to be 0.8 kJ mol⁻¹. The NPA, NBO and QTAIM approaches are used to probe covalency in the An–O_yl bond of AnO₂(H₂O)⁺, and all metrics agree that these bonds become increasingly covalent as the 5f series is crossed, providing rationalisation for the increasingly endothermic isomerisation reactions. QTAIM analysis indicates that the AnO and An–OH bonds in the oxide hydroxide isomers also become increasingly covalent as the 5f series is crossed.