Sequestration of Np4+ and NpO22+ ions by using diglycolamide-functionalized azacrown ethers in C8mim·NTf2 ionic liquid: Extraction, spectroscopic, electrochemical and DFT studies

Abstract

Complexation of Np4+ and NpO22+ ions was studied in a room temperature ionic liquid (C8mim•NTf2) using two multiple diglycolamide (DGA) ligands with three and four DGA arms tethered to the nitrogen atoms of the aza-9-crown-3 and -12-crown-4 scaffolds termed as LI and LII, respectively. The studies include solvent extraction, UV–visible spectrophotometry, cyclic voltammetry, and density functional theory (DFT). While the extraction of NpO22+ ion, as a function of the nitric acid concentration, resembled that of the ‘solvation’ mechanism, seen in case of neutral donor ligands in molecular diluent, an opposite trend was observed for the Np4+ ion suggesting a ‘cation-exchange’ mechanism often operating in the case of ionic liquid-based solvent systems. Slope analysis suggested formation of Np(NO3)]3+•L and NpO2(NO3)2•L extracted species for the extraction of Np4+ and NpO22+, respectively, in both the ligand systems. The complexation of the metal ions was supported by peak shifts in the UV–visible spectrophotometric as well as cyclic voltammetric studies. DFT studies were carried out to get structural information of the complexes.