Selective Separation and Coordination of Europium(III) and Americium(III) by Bisdiglycolamide Ligands: Solvent Extraction, Spectroscopy, and DFT Calculations

Abstract

Diglycolamide-based ligands have recently received increased attention due to their outstanding affinity for trivalent actinides and lanthanides. The structure optimization of the ligands, however, still remains a hot topic to achieve better extraction performance. In this work, we prepare and investigate three multidentate diglycolamide ligands for the selective separation of Eu­(III) over Am­(III) from a nitric acid solution to explore the effect on the extraction of alkyl groups on the nitrogen atoms in the center of the BisDGA ligands. The introduction of ethyl or isopropyl groups on the central nitrogen atoms greatly increased the distribution ratios of trivalent metal ions and enhanced the separation factor of Eu­(III) over Am­(III). The complexation behaviors of Eu­(III) and Am­(III) ions were studied by slope analyses, electrospray ionization mass spectrometry (ESI-MS), and extended X-ray absorption fine structure (EXAFS) spectroscopy. The results indicated that the trivalent metal ions were extracted as 1:2 and 1:3 complexes for all three BisDGA ligands during the extraction. Density functional theory (DFT) calculations verified the relevant experimental conclusion that the selectivity of THEE-BisDGA for Eu­(III) is better than that for Am­(III). The metal–DGA bonds in the ML3(NO3)3 complexes seem to be stronger than those in ML2(NO3)3 complexes.

Strong Periodic Tendency of Trivalent Lanthanides Coordinated with a Phenanthroline-Based Ligand: Cascade Countercurrent Extraction, Spectroscopy, and Crystallography

“…However, it is extremely difficult to separate Ans­(III) from Lns­(III) efficiently and conveniently. − It is believed that the separation of Lns­(III) and Ans­(III) with specifically designed ligands is an efficient and convenient method. , Researchers have developed a series of ligands and studied their applications in the separation of Lns­(III) and Ans­(III), − such as trialkylphosphine oxide (TRPO), , N,N,N′,N′ -tetraoctyl diglycolamide (TODGA), , and di­(2-ethylhexyl)­phosphoric acid (HDEHP). Due to the demand for the “CHON” principle and high selectivity, nitrogen heterocyclic ligands, ,− such as 2,6-bis­(5,6-dialkyl-1,2,4-triazin-3-yl)-pyridine (BTP), − 6,6′-bis­(5,6-dialkyl-1,2,4-triazin-3-yl)-2,2′-bypyridine (BTBP), , and 2,9-bis­(1,2,4-triazin-3-yl)-1,10-phenanthroline (BTPhen), − are considered to be the most promising ligands for research and application. − Therefore, to design a potential ligand to separate Ans­(III) over Lns­(III) with high efficiency and selectivity, our laboratory has successfully synthesized and characterized a novel lipophilic ligand, Et-Tol-DAPhen, which is applied in the selective separation of actinides over Eu­(III) in a highly acidic environment. − …”

Pyridine-di-phosphonates as chelators for trivalent f-elements: kinetics, thermodynamic and interfacial study of Am(iii)/Eu(iii) solvent extraction

“…Previously, it was shown that N,O-donor ligands were characterized by fast extraction kinetics 23,59,60 in terms of "test-tube" kinetics. In this work, extraction was carried out in a Lewis cell (see 2.4) with a constant stirring speed of each phase and with a stationary interface.…”

Molecular-scale understanding of diluent effects on ligand assembly for metal ion separations

“…Complexation of a REE ion with ligands is typically highly enthalpically favorable, and when calculated computationally yields a large negative energy of complexation, DF complex . [30][31][32][33] What is not captured by this approach are the positive DF contributions that can counteract the complexation favorability, a critical one being assembly of ligands into a geometry favorable for ion coordination, which necessarily occurs within a diluent. This is the DF assembly seen in Fig.…”