Experimental and theoretical insight into the complexation of tetra secondary butyl diglycolamide (TSBDGA) with trivalent f cations into ionic liquid

Ionic liquids have been emerged of as potential 'green' alternatives to the volatile organic compounds used in liquid-liquid biphasic extraction of metal ions. Their unique properties bring interesting chemistry during extraction of metal ions with respect to tuning the extraction mechanism, speciation, kinetics and energetics associated to it. Diglycolamide based ligands exhibited high selectivity towards the trivalent f cations due to their aggregation behaviour in the diluents. In view of this, it is imperative to understand the complexation of trivalent f cations into ionic liquid with tetra secondary butyl diglycolamide (TsBDGA). TsBDGA was found to form 1:1, 1:2 and 1:3 species predominantly with trivalent f cations. However, the complexation constant values for Nd³⁺ were found to be lower than those of the Eu³⁺ ion, as ascribed to lanthanide contraction. The complexation was found to be spontaneous in nature. On complexation, the local asymmetry around Eu³⁺ was found to increase and the diffusion coefficient values were reduced. The complexation was also indicated by shifts in the carbonyl stretching frequency in the FTIR spectra. Computation analyses were performed to optimize the energy, bond length and 3D structures of the Nd³⁺ as well as Eu³⁺ complexes in gas phase and solution phase alongwith the calculation of the Mulliken Partial atomic charge.