Lipophilic phenanthroline diamide ligands in 1-octanol for separation of Am(III) from Eu(III)

Abstract

Although phenanthroline diamide (DAPhen) ligands have recently shown vast opportunity in group separation of actinides, the commonly used diluents in research, such as cyclohexanone with highly aqueous intersolubility, and 1-(trifluoromethyl)− 3-nitrobenzene with strong toxicity and corrosiveness, are becoming clear demerits. Herein, several lipophilic N,N′-dialkyl-N,N′-diphenyl-2,9-diamide-1,10-phenanthroline (R-Ph-DAPhen) ligands were synthesized and employed for selective separation of Am(III) from Eu(III) in 1-octanol, a practical low-toxicity and low-corrosive solvent. The solvent extraction results confirm their separation effect toward Am(III) over Eu(III) in both 1-octanol and TBP/1-octanol (v/v, 3/7) systems. Spectroscopic analysis illustrates that the ligands simultaneously generate M:L= 1:1 and 1:2 complexes with Ln(III), depending on the molar ratio of metal ion to ligand. The steric hindrance caused by the length of the alkyl side chains greatly affects the coordination chemistry of these ligands. Density functional theory (DFT) calculations shed light that these R-Ph-DAPhen ligands have desired An(III) affinity over Ln(III), and compared with F-3 solvent, 1-octanol weakens the extraction ability of the ligands for both lanthanides and actinides. This work contributes to further understanding of the extraction behavior of phenanthroline diamide-based ligands in different solvents and pushing them forward into practical applications in real An(III) extraction.