A potentiometric study on thermodynamic of Th(IV) complexation

The stability constant of U(VI)-succinate complex was found to increase with temperature whereas the protonation constants remained nearly constant. The increase in log K with temperature could be well explained in terms of Born equation for electrostatic interaction between metal ion and ligand anion. The protonation as well as complexation reactions were found to become more endothermic with temperature. However, in the complexation reaction, the increase in enthalpy was overcompensated by the increase in entropy making the reaction more favorable at higher temperatures. The ΔCP of complexation was constant in the temperature range 25–65°C. The ΔCP of U(VI)-succinate is higher than that for U(VI)-oxalate and U(VI)-malonate, which has been explined on the basis of their molecular structures