Soft-donor dipicolinamide derivatives for selective actinide(III)/lanthanide(III) separation: the role of S- vs. O-donor sites

Selectivity for An(III) vs. Ln(III) binding and extraction using dipicolinamide analogs containing the CO vs. CS groups was investigated in solution and the gas-phase, and by DFT calculations. The results show higher selectivity for complex formation and extraction for Am(III) vs. Eu(III) for the softer dithioamide vs. the diamide ligand, while in CH₃CN the diamide binds more strongly than the thioamide to several Ln(III), forming 1 : 1 complexes.