Binary and ternary complexation of NpO_2~+ with carboxylate and aminocarboxylate ligands

摘要

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 6.60m 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 6.60m 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.