Enhancing the Selectivity of Trivalent Actinide over Lanthanide Using Asymmetrical Phenanthroline Diamide Ligands

Abstract

Phenanthroline diamide ligands have been widely used in the separation of trivalent actinides and lanthanides, but little research has focused on extractants with asymmetrical substitutes. Two novel asymmetrical phenanthroline-based ligands N 2,N 2,N 9-triethyl-N 9-tolyl-1,10-phenanthroline-2,9-dicarboxamide (DE-ET-DAPhen) and N 2-ethyl-N 9,N 9-dioctyl-N 2-tolyl-1,10-phenanthroline-2,9-dicarboxamide (DO-ET-DAPhen) were first synthesized in this work, whose extraction ability and complexation mechanism to trivalent actinides [An­(III)] and lanthanides [Ln­(III)] were systematically investigated. The ligands dissolved in n-octanol exhibit good extraction ability and high selectivity toward Am­(III) in acidic solutions. The complexation mechanism of the ligands with Ln­(III) in solution and solid state was analyzed using slope analysis, 1H NMR spectrometric titration, ESI-MS, and calorimetric titration. It is revealed that the ligands complex with Am­(III)/Eu­(III) with 1:1 stoichiometry. The stability constant (log β) of the complexation reaction of Eu­(III) with DE-ET-DAPhen determined by UV–vis spectrophotometric and calorimetric titration is higher than that of DO-ET-DAPhen, indicating the stronger complexation ability of DE-ET-DAPhen. Meanwhile, the calorimetric titration results show that the complexation process is exothermic with a decreased entropy. The structures of 1:1 complexes of Eu­(III) and Nd­(III) with DE-ET-DAPhen were analyzed through single-crystal X-ray diffraction. This work proves that ligands containing asymmetrical functional groups are promising for An­(III)/Ln­(III) separation, which shows great significance in efficient extractants designed for the spent nuclear fuel reprocessing process.

Separation and Complexation of Lanthanides with an Acidic Phenanthroline Carboxamide Ligand: Extraction, Spectroscopy, and Crystallography

“…The resulting higher electron density and basicity of heavy lanthanide would provide a stronger interaction with NaDOAPA, which could explain the higher extraction efficiency of heavy lanthanides . The log β of Eu­(III) with symmetrical DAPhen ligands has been reported . The log β of the 1:1 complex of Eu­(III) with N , N , N ′, N ′-tetraoctyl-1,10-phenanthroline-2,9-dicarboxamide (Oct-Oct-DAPhen) in CH 3 CN was determined to be 4.60 ± 0.01, 1.6 lower than that of the 1:1 Eu­(III) complex with NaDOAPA.…”

6-(6-Methyl-1,2,4,5-Tetrazine-3-yl)-2,2′-Bipyridine: A N-Donor Ligand for the Separation of Lanthanides(III) and Actinides(III)

“…In this pursuit, solvent extraction stands out as a promising approach, requiring the use of well-designed complexing agents. While conventional oxygen-donor ligands may lack the desired selectivity, nitrogen or sulfur-donor ligands, with their softer characteristics, display a significantly higher selectivity for trivalent minor actinides compared to the lanthanides. ,− Current developments of mixed N,O-donor ligands aim at combining the high metal binding affinity of O-donor ligands with the desired selectivity of N-donor ligands. − Unfortunately, most of these compounds are ineffective when extracting from solutions with a high nitric acid concentration (>0.5 mol L –1 HNO 3 ), which is necessary for the PUREX process. Alkyl-substituted 2,6-ditriazinylpyridines (BTP), − alkylated 6,6′-ditriazinylbipyridines (BTBP), − and their phenanthroline derivatives (BTPhen) , have been developed and can directly extract trivalent actinides from nitric acid solutions with a high selectivity over the lanthanides.…”