Unsymmetrical Amide-lactam-phenanthroline (ALPhen) Extractant for Selective Separation of Actinides and Lanthanides

The
phenanthroline diamide (DAPhen) extractants demonstrate remarkable
selectivity in trivalent actinide/lanthanide separation. To enhance
the extraction performance of DAPhen derivatives, partial lactamization
was strategically introduced into the architecture. Two unsymmetrical
extractants possessing flexible amide and rigid lactam functional
groups were synthesized: N,12-diethyl-9-methyl-13-oxo-N-(p-tolyl)-12,13-dihydroquinolino[3,4-b][1,10]phenanthroline-2-carboxamide (EtTol–EtTol-ALPhen)
and N,N-dibutyl-12-ethyl-9-methyl-13-oxo-12,13-dihydroquinolino[3,4-b][1,10]phenanthroline-2-carboxamide (But2-EtTol-ALPhen).
The ligand EtTol–EtTol-ALPhen achieved superior Am(III)/Eu(III)
selectivity (SFAm/Eu > 100, 2.0 M HNO3) and
favorable Am(III) distribution ratios (DAm ≈ 10, 2.0–4.0 M HNO3) in n-octanol. The coordination behavior was explored using 1H NMR titration, ESI-MS, and UV-vis spectrophotometric titration,
revealing 1:1 and 1:2 metal-to-ligand binding stoichiometries. Single-crystal
X-ray diffraction analysis confirmed the formation of ML (NO3)3 and ML2(H2O)23+ species in the NO3– and ClO4– systems, respectively.
Furthermore, density functional theory (DFT) calculations offered
theoretical insights into ligand–metal interactions from the
electronic structure and thermodynamics. This work balances extraction
capability and solubility through preorganization optimization, offering
a reference for future extractant design.

邻菲罗啉二酰胺（DAPhen）萃取剂在三价锕系/镧系元素分离中展现出优异的选择性。为优化DAPhen衍生物的萃取性能，研究人员通过策略性手段在其分子结构中引入了部分内酰胺化修饰。本研究合成了两种兼具柔性酰胺与刚性内酰胺官能团的不对称萃取剂：N,12-二乙基-9-甲基-13-氧代-N-(对甲苯基)-12,13-二氢喹啉并[3,4-b][1,10]邻菲罗啉-2-甲酰胺（EtTol–EtTol-ALPhen）以及N,N-二丁基-12-乙基-9-甲基-13-氧代-12,13-二氢喹啉并[3,4-b][1,10]邻菲罗啉-2-甲酰胺（But2-EtTol-ALPhen）。配体EtTol–EtTol-ALPhen在正辛醇体系中展现出优异的Am(III)/Eu(III)分离选择性（SFAm/Eu > 100，2.0 M硝酸体系）与良好的Am(III)分配比（DAm ≈10，2.0~4.0 M硝酸体系）。研究人员通过氢核磁共振（1H NMR）滴定、电喷雾电离质谱（ESI-MS）以及紫外-可见分光光度滴定等手段探究了该配体的配位行为，揭示了1:1与1:2两种金属-配体结合计量比。单晶X射线衍射分析证实，在硝酸根（NO3–）与高氯酸根（ClO4–）体系中分别生成了ML(NO3)3与ML2(H2O)23+配合物。此外，密度泛函理论（DFT）计算从电子结构与热力学层面为配体-金属相互作用提供了理论解析。本研究通过预组织化优化实现了萃取性能与溶解性的平衡，为后续萃取剂的分子设计提供了参考依据。