Completely preorganized bis-lactam-1,10-phenanthroline ligands with high stability for efficient separation of Am(<scp>iii</scp>) over Eu(<scp>iii</scp>)

N,O-Heterocyclic ligands such as 2,9-diamide-1,10-phenanthroline dicarboxamide (DAPhen) and bis-lactam-1,10-phenanthroline (BLPhen) exhibit excellent separation performance for Am(III) and Eu(III) in high-level liquid waste. However, DAPhen-based ligands show poor extraction capacity, and BLPhen ligands suffer from decomposition in acidic solutions, which hinders their application in practical separation processes. To develop ligands with superior performance, two new completely preorganized and highly stabilized bis-lactam-1,10-phenanthroline (BLPhen) ligands with varying alkyl chain lengths were synthesized, demonstrating exceptional extraction and separation of Am(III) from Eu(III) with maximum separation factors of 68 and 53, respectively. DFT calculations and various analytical techniques confirmed that the ligands form 1 : 1 complexes with metal ions, with stronger bonding interactions for Am(III), highlighting their potential for spent nuclear fuel processing.