Binary and ternary complexation of NpO₂ ⁺ with carboxylate and aminocarboxylate ligands

Abstract

The complex formation of NpO 2 + with carboxylates: oxalic acid (Ox), malonic acid (Mal) succinic acid (Suc); glutaric acid (Glu), methylmalonic acid (Memal), oxydiacetic acid (ODA), TDA (thiodiacetic acid) and citric acid (Cit) and aminocarboxylates: iminodiacetic acid (IDA), methyliminodiacetic acid (MIDA),nitrilotriacetic acid (NTA), 2-hydroxyethylethylenediamine triacetic acid (HEDTA),ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) was studied by solvent extraction in 6.60 m NaClO 4 at 25 ∘ C. The formation of only the 1 : 1 NpO 2 + complex was observed with the ligands under investigation. The complexation of NpO 2 + with Ox, IDA, ODA and TDA was also measured at variable temperatures ranging from 25-60 ∘ C in 6.60 m NaClO 4 . Results show that the complexation of NpO 2 + with these ligands increases with increasing temperature.The enthalpy and entropy of complexation of NpO 2 + were calculated from the temperature dependence of the stability constants using the Van't Hoff equation. Additionally, the formation of an aqueous ternary complex of the form NpO 2 (X)(L) (X = EDTA or HEDTA; L = Ox or ODA) was identified for NpO 2 + at 25 ∘ C. Stabilities of these complexes are measured and discussed in term of their structures and basicities.