Thermodynamics and the structural aspects of the ternary complexes of Am(iii), Cm(iii) and Eu(iii) with Ox and EDTA + Ox

Abstract

The stability constants and the associated thermodynamic parameters of formation of the binary and the ternary complexes of Am³⁺, Cm³⁺ and Eu³⁺ were determined by a solvent extraction to measure the variation in the distribution coefficient with temperature (0–60 °C) for aqueous solutions of I = 6.60 m (NaClO₄). The formation of ternary complexes is favored by both the enthalpy (exothermic) and the entropy (endothermic) values. ¹³ C NMR, TRLFS and EXAFS spectral data was used to study the coordination modes of the ternary complexes. In the formation of the complex M(EDTA)(Ox)³⁻, the EDTA retained all its coordination sites with Ox binding via two carboxylates and with one water of hydration remaining attached to the M³⁺. In the complex M(EDTA)(Ox)₂⁵⁻, one carboxylate, either from EDTA or Ox, is not bounded to M³⁺ and there were no water of hydration attached to these cations