Theoretical Insights into the Selective Extraction of Americium(III) over Europium(III) with Dithioamide-Based Ligands

Abstract

Separation of trivalent actinides An­(III) from lanthanides Ln­(III) is a worldwide challenge owing to their very similar chemical behaviors. It is highly desirable to understand the nature of selectivity for the An­(III)/Ln­(III) separation with various ligands through theoretical calculations because of their radiotoxicity and experimental difficulties. In this work, we have investigated three dithioamide-based ligands and their extraction behaviors with Am­(III) and Eu­(III) ions using the scalar-relativistic density functional theory. The results show that the dithioamide-based ligands have stronger electron donating ability than do the corresponding diamide-based ones. All analyses including geometry, Mulliken population, QTAIM (quantum theory of atoms in molecules), and NBO (natural bond orbital) suggest that the Am–S/N bonds possess more covalency compared to the Eu–S/N bonds, and the M–S bonds have more covalent character than the M–N bonds. Thermodynamic results reveal that N 2,N 9-diethyl-N 2,N 9-di-p-tolyl-1,10-phenanthroline-2,9-bis­(carbothioamide) (L 1 ) has a stronger complexing ability with metal ions owing to its rigid structure and that N 6,N 6′-diethyl-N 6,N 6′-di-p-tolyl-[2,2′-bipyridine]-6,6′-bis­(carbothioamide) (L 2 ) shows a higher selectivity for the Am­(III)/Eu­(III) separation. In addition, these dithioamide-based ligands possess Am­(III)/Eu­(III) selectivity higher than those of the corresponding diamide-based ones, although the former have weaker complexing ability with metal ions, probably due to the greater covalency of the M–S bonds. This theoretical evaluation provides valuable insights into the nature of the selectivity for the Am­(III)/Eu­(III) separation and information on designing of efficient An­(III)/Ln­(III) separation with dithioamide-based ligands.

Insights into complexation and enantioselectivity of uranyl‐2‐(2‐hydroxy‐3‐methoxyphenyl)‐9‐(2‐hydroxyphenyl)thiopyrano[3,2‐h]thiochromene‐4,7‐dione with R/S‐organophosphorus pesticides

“…It is generally considered that the atom corresponding to the place where the ESP is negative is a nucleophilic site. [ 4,19 ] It is obvious from Figure 3 that the blue region is mainly concentrated around the sulfur and oxygen atoms, and the negative region of HTTDN is also mainly present in the cavity of the ligand. Moreover, the two smallest extreme points also appear here, the value of the extreme point close to the O 3 atom is −40.92 kcal mol −1 , and the value of the extreme point around the O 4 atom is −38.27 kcal mol −1 , revealing that O 3 has greater coordination affinity for uranyl than O 4 .…”

“…Studies showed that for pyridylpyrazole ligands, increasing the bridging skeleton was more conducive to improving the extraction and separation ability than increasing the side chain. Wang et al [ 19 ] theoretically explored the relationship between three dithioamide‐based ligands and Am(III)/Eu(III) selectivity and broadened the understanding of the separation mechanism between Am(III)/Eu(III) and dithioamide‐based ligands.…”

Impact of Coordination Modes of N‐Donor Ligands on Am(III)/Eu(III) Separation in Nuclear Waste Water Treatment – A DFT Study

“…The ability of the ligands to attract metal atoms is often influenced by the charge on the coordinating atoms of the ligands. [14] Consequently, the charges present on the metal, oxygen and nitrogen atoms have been calculated and analysed (Figure 5 and Supporting Information Table 2 (SIT-2)). Results show that the nitrogen atoms have a lower negative charge than that of the oxygen atoms.…”

Solution Structure of a Europium-Nicotianamine Complex Supports That Phytosiderophores Bind Lanthanides

“…10a, and a depiction of selected valence MOs are shown in Figure 10b. We focused on analysis of the valence orbitals rather than the electronic excitations, because, as shown in previous studies, 87,88 such analysis is sufficient to qualitatively elucidate coordination properties.…”