Theoretical study on complexation of U(VI) with ODA, IDA and TDA based on density functional theory

This study aims to understand the complexation of U(VI) with oxydiacetic acid (ODA), iminodiacetic acid (IDA) and thiodiacetic acid (TDA) through density functional theory (DFT) calculations. The structures, complexation stabilities and bonding nature were investigated for U(VI)/XDA complexes (XDA is short for the three ligands). The calculations have proved that tridentate structures are more favorable than terminal bidentate ones for all stoichiometries, and steric hindrance is a factor that cannot be ignored especially for 1 : 2 complexes. The binding stabilities of the ligands and relative binding groups are in the sequences IDA > ODA >> TDA and C=O > OH- >> H2O > X (O-ether, N and S), respectively. All of the coordination bonds exhibit typically ionic character. The coordination bonds are mainly contributed by the interactions of U 5f-orbital and O(=C)/X p-orbitals. The strength of all coordination bonds follows the order U-O(=C) > U-N > U-O(H-2) approximate to U-O-ether > U-S. U-S interaction was solidly confirmed by MO and AIM analysis, which is found for U(VI)/TDA complexes for the first time. U-X bonds play an important role in U(VI)/XDA coordination.