Selective extraction and complexation of trivalent actinide and lanthanide by tetradentate N,O-Hybrid phenanthroline derived ligands

Phenanthroline derived diamide ligand featured with N- and O-donors is one of promising extractants for the selective separation of trivalent actinides (An) over lanthanides (Ln). In the present work, three representative isopropyl (L1), 2,6-dimethylpiperidin-1-yl (L2) and morpholino (L3) grafting 2,9-diamide-1,10-phenanthroline (DAPhen) ligands were synthesized and the application in solvent extraction of trivalent americium (Am) and europium (Eu) in an ionic liquid (IL), C4mimNTf2, was probed. Slope analysis suggests the 2:1 ligand/metal complex as the dominant species in the case of extracting Am(III). While both 2:1 and 1:1 complexes are generated during the extraction of Eu(III). The relationships between molecular structures and extraction behaviors are elucidated involving electric and steric effects. Meanwhile, complexation studies in combination with absorption spectrophotometry, luminescence spectrophotometry, 1H NMR spectrometry and single crystal X-ray diffraction as well as theoretical analyses further elaborate the extraction mechanisms. This study uncovers more in-depth experimental insights into the design of more efficient DAPhen ligands for Am(III)/Ln(III) separation.