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Two new phosphine oxide‐functionalized 1,10‐phenanthroline ligands, tetradentate 2,9‐bis(butylphenylphosphine oxide)‐1,10‐phenanthroline (BuPh‐BPPhen, L1) and tridentate 2‐(butylphenylphosphine oxide)‐1,10‐phenanthroline (BuPh‐MPPhen, L2), were synthesized and studied comparatively for their coordination with trivalent actinides and lanthanides. The complexation mechanisms of these two ligands toward trivalent f‐block elements were thoroughly elucidated by NMR spectroscopy, UV/vis spectrophotometry, fluorescence spectrometry, single‐crystal X‐ray diffraction, solvent extraction, and theoretical calculation methods. NMR titration results demonstrated that 1 : 1 and 1 : 2 (metal to ligand) lanthanides complexes formed for L1, whereas 1 : 1, 1 : 2 and 1 : 3 lanthanide complexes formed for L2 in methanol. The formation of these species was validated by fluorescence spectrometry, and the corresponding stability constants for the complexes of NdIII with L1 and L2 were determined by using UV/vis spectrophotometry. Structures of the 10‐coordinated 1 : 1‐type complexes of EuL1(NO3)3 and [EuL2(NO3)3(H2O)] Et2O in the solid state were characterized by X‐ray crystallography. In solvent‐extraction experiments, L1 exhibited extremely strong extraction ability for both AmIII and EuIII, whereas L2 showed nearly no extraction toward AmIII or EuIII due to its high hydrophilicity. Finally, the structures and bonding natures of the complex species formed between AmIII/EuIII and L1/L2 were analyzed in DFT calculations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soft-hard combined phenanthroline ligands show excellent extraction to actinide. • Rigid preorganized phenanthroline skeleton is helpful to promote the extraction. • Combination of soft and hard atoms can improve the separation ability of An/Ln. The chemical separation of minor actinides (MAs) over lanthanides from high-level waste (HLW) is one of the hottest and most difficult topics in international separation science. N, O-hybrid phenanthroline-derived extractants have shown good potential in the separation of minor actinides over lanthanides from highly acidic HNO 3 solution by liquid–liquid solvent or solid extraction method. The 1,10-phenanthroline skeleton can serve as a platform to design various extractants for the separation of actinides. In this review, the recent progress made in the hard-soft donors combined 1,10-phenanthroline type extractants for separation and complexation with f-block elements is summarized. The structure–activity relationships between the extractants and their separation performances are discussed, which can provide practical strategies to design more efficient extractants for actinides separation. Finally, the future perspectives and trends in those phenanthroline-derived extractants for actinides separation are proposed. [ABSTRACT FROM AUTHOR]

As representatives of actinyl and bare actinide ions, U(VI) and Th(IV) show different solvent extraction performance and complexation mechanisms with phenanthroline phosphonate (POPhen) ligands. [Display omitted] • Phenanthroline phosphonate extractants show strong extraction ability toward U(VI) and Th(IV) in high acidity. • The complexation mechanism of phenanthroline phosphate with U(VI) and Th(IV) has been thoroughly studied. • Increasing carbon chain substituents can enhance the extraction capacity for tetravalent and hexavalent actinides. The extraction and separation of actinide over lanthanide elements is a key step in the spent fuel reprocessing process, which involves a variety of actinides with different valence states. The phenanthroline phosphonate (POPhen) extractants have a strong ability to extract trivalent actinides over lanthanides from highly acidic HNO 3 solution with good separation ability of An(III) over Ln(III). However, the extraction properties and complexation mechanism of POPhen extractants for high-valence actinides have yet to be studied. In this work, U(VI) and Th(IV) were selected as representatives of high-valence actinides to systematically study the extraction effect and complexation mechanism of C2-POPhen and C4-POPhen with them. The results showed that POPhen extractants had excellent coordination and extraction ability for U(VI) and Th(IV) under highly acidic nitrate conditions. The extraction capacity of C4-POPhen was stronger than that of C2-POPhen, and both ligands hold a stronger extraction capacity for Th(IV) than U(VI) under the same experimental conditions. Both the slope analysis and spectroscopic studies indicated that POPhen extractants could form the sole 1:1 complexes with U(VI) and both 1:1 and 1:2 metal-to-ligand complexes with Th(IV). The structures of the 1:1 and 1:2 Th(IV) complexes with POPhen-type extractants were first elucidated by X-ray crystallography. This study will be helpful to deepen the understanding of the extraction effect and complexation mechanism of POPhen with high-valence actinide elements, providing a fundamental data basis and theoretical reference for the development of the advanced subsequent actinides separation process. [ABSTRACT FROM AUTHOR]