Complexation of tetraalkyl diglycolamides with trivalent f-cations in a room temperature ionic liquid: extraction and spectroscopic investigations

Abstract

This paper reports the complexation of a series of tetraalkyl diglycolamides (TRDGA) with trivalent f-cations in a room temperature ionic liquid, viz., 3-octyl-1-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C₈mim][Tf₂N]). The stability constants of TRDGA/Nd³⁺ complexes (where R = n-pentyl, n-hexyl, n-octyl, n-decyl and 2-ethylhexl) were determined by absorbance spectroscopy. All the DGA ligands formed a 1 : 3 (Nd³⁺/DGA) complex as the limiting species. Solvent extraction data on Am³⁺ and Eu³⁺ were obtained with the TRDGA ligands in [C₈mim][Tf₂N] to arrive at a correlation between their extraction behaviour and complexation constant. The nature of the complex formed in the single phase titration (in [C₈mim][Tf₂N]) and those extracted in the [C₈mim][Tf₂N] medium from the aqueous phase were found to be identical. Fluorescence lifetime data confirmed that, in both single phase titration and biphasic solvent extraction, the complexation proceeded via replacement of water molecules from the primary coordination sphere of the metal ion. The spectroscopic data confirmed the absence of NO₃⁻ and Tf₂N⁻ ions or H₂O in the extracted complexes.