Selective complexation of trivalent americium over europium with substituted Triazolebipyridine-based ligand in high Level-Liquid Waste- A DFT Investigation

Similar chemical properties like ionic radius and oxidation states exhibited by trivalent actinides (An(III)) and lanthanides (Ln(III)) pose a challenge for their separation in reprocessing of spent nuclear fuel. For this purpose, we explore the 6,6' -bis(1-(2-ethylhexyl)-1H-1,2,3-triazol-4-yl)-2,2'-bipyridine (EH-BTzBP) ligand from a theoretical perspective aiming to tune its selectivity through substitutions. The effect of strong, moderate, and weak electron-withdrawing groups (EWGs) on the selectivity of the ligand has been studied using scalar relativistic quantum chemistry calculations. The results reveal that among the four ligating nitrogen atoms, nitrogen on triazole rings contribute more to the complexation compared to the other two nitrogens of bipyridyl (bpy) moiety. According to the quantum theory of atoms in molecules (QTAIM) analysis, Eu complexes show bifurcate interactions between the nitrogen atom of ligand and oxygen of metal nitrate, while such bonds are absent in Am complexes. The EWGs have been identified to enhance the selectivity of the EH-BTzBP ligand in general and nitro group in particular, to show exceptional selectivity towards Am(III) over Eu(III). Our study could render new insights in understanding the effect of EWGs in tuning the selectivity of Bis-1,2,3-triazolebipyridine derivatives and pave the way for designing substituted ligands with better selectivity for the separation process.