Unusual extraction of trivalent f-cations using diglycolamide dendrimers in a room temperature ionic liquid: Extraction, spectroscopic and DFT studies

The complexation of Am³⁺ and Eu³⁺ was studied with three generations of diglycolamide (DGA)-functionalized poly(propylene imine) diaminobutane dendrimers (DGA-Den) with two, four and eight DGA moieties by solvent extraction and luminescence spectroscopy in a room temperature ionic liquid, viz. 3-butyl-1-methyl imidazolium bis(trifluoromethanesulfonyl)imide ([C₄mim][Tf₂N]). The extraction of trivalent f-cations was found to increase with decreasing HNO₃ concentrations conforming to a cation exchange mechanism with the extraction of Eu³⁺ being higher than that of Am³⁺ in the acid concentration range of 0.01-6.0 M HNO₃. The nature of the extracted species showed unusual trends compared to those reported previously in molecular diluents. Fluorescence lifetime data suggested the absence of H₂O in the extracted complexes meaning strong inner-sphere complexes. The nature of the extracted complexes predicted by solvent extraction was supported by DFT computations.