Selective Separation of Am(III)/Eu(III) by the QL-DAPhen Ligand under High Acidity: Extraction, Spectroscopy, and Theoretical Calculations

Abstract

Although 1,10-phenanthroline-based ligands have recently shown vast opportunities for the separation of trivalent actinides (Ans(III)) from lanthanides (Lns(III)), the optimization and design of the extractant structure based on the phenanthroline framework remain hotspots for further improving the separation. Following the strategy of hard and soft donor atom combination, for the first time, the quinoline group was attached to the 1,10-phenanthroline skeleton, giving a lipophilic ligand, 2,9-diacyl-bis((3,4-dihydroquinoline-1((2H)-yl)-1),10-phenanthroline (QL-DAPhen)), for Am(III)/Eu(III) separation. In the presence of sodium nitrate, the ligand can effectively extract Am(III) over Eu(III) in HNO 3 solution, with the separation factor (SF Am/Eu ) ranging from 29 to 44. The coordination chemistry of Eu(III) with QL-DAPhen was investigated by slope analysis, NMR titration, UV−vis titration, Fourier transform infrared spectroscopy, electrospray ionization-mass spectrometry, and theoretical calculations. The experimental results unanimously confirm that the ligand forms both 1:1 and 1:2 complexes with Eu(III), and the stability constants (log β) of each of the two complexes were obtained. Density functional theory calculations show that the Am−N bonds have more covalent characteristics than the Eu−N bonds in the complexes, which reveals the reason why the ligand preferentially bonds with Am(III). Meanwhile, the thermodynamic analysis reveals that the 1:1 complex is more thermodynamically stable than the 1:2 complex. The findings of this work have laid a solid theoretical foundation for the application of phenanthrolinebased ligands in the separation of An(III) from practical systems.

Theoretically exploring the bonding properties of trivalent transuranic elements with 2‐(2‐amino‐2‐oxyethoxy) acetic acid

“…In this study, BP86 [22, 23], B3LYP [24, 25] and PBE0 [26] methods are used for optimization calculation. Because BP86 method has shown good performance in this study and performed well in previous theoretical work of similar systems [20, 27, 28], this method is finally adopted for in‐depth exploration. For Np, Pu, Am, Cm, Bk atoms, 60 core electrons are treated by quasi‐relativistic effective core potentials (RECPs).…”

Theoretically investigating the ability of phenanthroline derivatives to separate transuranic elements and their bonding properties

“…18 Some theoretical studies show that the BP86 19,20 functional can well reproduce the experimental geometries and ground state properties of f-element compounds with satisfactory accuracy, 21,22 and it also shows good performance in the previous theoretical work of similar systems. 20,23,24 Therefore, we adopted BP86 to optimize the geometric configuration of the complexes AnL(NO 3 ) 3 and [AnL 2 (NO 3 )] 2+ (An = Np, Pu, Am, Cm; L= L triazol , L pyrazol , L pyrrol ), and finally obtained the stable configurations without virtual frequencies. It is shown that spin-orbit coupling has a negligible influence on the configuration and thermodynamic analysis of the system due to the unchanging oxidation state of the actinide ions.…”

Selective Complexation and Separation of Uranium(VI) from Thorium(IV) with New Tetradentate N,O-Hybrid Diamide Ligands: Synthesis, Extraction, Spectroscopy, and Crystallographic Studies

“…The past decade has witnessed a flourishing development of actinide/lanthanide complexation and separation by employing N,O-hybrid ligands based on rigid N-heterocyclic skeletons. − Shi et al reported a tetradentate N,O-hybrid ligand, N , N ′-diethyl- N , N ′-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen), with well-preorganized amide oxygen and nitrogen atoms, which exhibits good extraction ability and selectivity toward actinides over lanthanides . More recently, Zabierowski et al reported that 2,2′-bipyrimidine-4,4′-dicarboxylic acid could bind to lanthanides to form stable complexes, in which the pyrimidine nitrogen atoms and carboxylic oxygen atoms involved in coordination on the same molecule always lie approximately in the same plane.…”