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

The complex formation of NpO2+ 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 NaClO4 at 25 C. The formation of only the 1: 1 NpO2+ complex was observed with the ligands under investigation. The complexation of NpO2+ with Ox, IDA, ODA and TDA was also measured at variable temperatures ranging from 25-60 C in 6.60 m NaClO4. Results show that the complexation of NpO2+ with these ligands increases with increasing temperature. The enthalpy and entropy of complexation of NpO2+ 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 NpO2(X)(L) (X = EDTA or HEDTA; L = Ox or ODA) was identified for NpO2+ at 25 C. Stabilities of these complexes are measured and discussed in term of their structures and basicities.