Theoretical evaluation of mixed N-, O- donor based TMPhenDA ligand in selective complexation with actinide (III) ions over lanthanide (III) ions

Separation of trivalent actinides An(III) from lanthanide Ln(III) is an extremely challenging task in handling nuclear wastes due to their similar chemical behaviours. Though many designed organic ligands have been used for the separation of Ln(III) from An(III) over the years, selectivity and efficiency is still a matter of concern. This drives us to formulate new efficient ligands, in which mixed –N, –O donor ligands are one of the most emerging and promising agents in separation of An(III) from Ln(III). In this work, recently reported TMPhenDA ligand has been investigated for their complexation behaviour with An(III) (U, Am, Cm) and Ln(III) (Nd, Eu, Gd) ions using scalar relativistic ZORA/DFT calculations. Computed bond parameters show that the An(III) ions bind strongly to the ligand than the lanthanide ions. Bond order and QTAIM analyses have been done on the optimized geometries to understand the bonding situation present in the M³⁺TMPhenDA complexes. Further, energy decomposition analysis is taken up to assign the percentage covalency of M-N and M-O bonds in these complexes to estimate the strength of these bonds. Overall, this computational investigation provides an in-depth understanding on the preferential selectivity of the ligand with An(III) over Ln(III) using DFT calculations.