Complexation thermodynamics and the structure of the binary and the ternary complexes of Am, Cm and Eu with CDTA and CDTA + IDA

The stability constants and the thermodynamic parameters of the formation of the binary complexes of trivalent Am³⁺, Cm³⁺ and Eu³⁺ with CDTA and of their ternary complexes with CDTA + IDA were determined by solvent extraction measurements in aqueous solutions of I = 6.60 m (NaClO₄) at temperatures of 0-60 °C. The endothermic enthalpy and the positive entropy values reflect the significant effects of cation dehydration and of the rigidity of the ligand structure in the formation of these complexes. TRLFS and NMR (¹H and ¹³C) data provided information on the structure of the ternary complexes in solution. The size and rigidity of CDTA affect the binding mode of IDA in the complexation of M(CDTA)(IDA)(H₂O)³⁻ and M(CDTA)(IDA)³⁻ in which IDA has a bidentate coordination mode in the former and a tridentate coordination mode in the latter.