Thermodynamics and the structure of binary and ternary complexation of Am3+ Cm3+ and Eu3+ with DTPA and DTPA + IDA

The formation, their stability and the thermodynamic parameters of the binary complexation of Am3+, Cm3+ and Eu3+ with DTPA and of the ternary complexation of DTPA + IDA were studied in aqueous solutions of I = 6.60 m (NaClO4) and temperatures of 0–60 °C by solvent extraction technique. The stability constants of these complexes increased with increasing temperature. Positive enthalpy and the large entropy values for the binary and the ternary complexation indicated significant effect of cation dehydration at such high ionic strengths. TRLFS and NMR (1H and 13C) data provided insight into the structure of the ternary complexes in solution. In the binary [M(DTPA)]2− complex, M3+ binds via five carboxylates and three nitrogens, while in the ternary complex [M(DTPA)(IDA)]4−, DTPA binds by the same eight coordination sites and IDA binds via one of its carboxylate anion groups.