Theoretical Insights on the Complexation of Americium(III) and Europium(III) with Diglycolamide- and Dimethylacetamide-Functionalized Calix[4]arenes

Abstract

Separation of minor actinides from lanthanides is one of the biggest challenges in spent fuel reprocessing due to the similar physicochemical properties of trivalent lanthanides (Ln­(III)) and actinides (An­(III)). Therefore, developing ligands with excellent extraction and separation performance is essential at present. As an excellent pre-organization platform, calixarene has received more attention on Ln­(III)/An­(III) separation. In this work, we systematically explored the complexation behaviors of the diglycolamide (DGA)/dimethylacetamide (DMA)-functionalized calix­[4]­arene extractants for Eu­(III) and Am­(III) using relativistic density functional theory (DFT). These calix[4]­arene-derived ligands were obtained by functionalization with two or four binding units at the narrow edge of the calix[4]­arene platform. All bonding nature analyses suggested that the Eu-L complexes possess stronger interaction compared to Am-L analogues, resulting in the higher extraction capacity of the these calix[4]­arene ligands toward Eu­(III). Thermodynamic analysis demonstrates that these pre-organized ligands on the calix[4]­arene platform with four binding units yield better extraction abilities than the single ligands. Although DMA-functionalized ligands show stronger complexation stability for metal ions, in acidic solutions, the calix[4]­arene ligands with DGA binding units have better extraction performance for Eu­(III) and Am­(III) due to the basicity of the DMA ligand. This work enabled us to gain a deeper understanding of the bonding properties between supramolecular ligands and lanthanides/actinides and afford useful insights into designing efficient supramolecular ligands for separating Ln­(III)/An­(III).

Thorium Complexation with Aliphatic and Aromatic Hydroxycarboxylates: A Combined Experimental and Theoretical Study

“…Researchers have developed the ligands utilizing the principle of hard–soft acid–base for the separation of An­(III) and Ln­(III). Diamide ligand-based extractants, where the presence of nitrogen provides softness, are used for the separation of An­(III) and Ln­(III). − Hydroxycarboxylic acids, namely, α-hydroxyisobutyric acid (HIBA) − and mandelic acid (MA) (Scheme ), have been well-known eluting reagents for the liquid chromatographic separation of actinides and lanthanides. − Reports showed that the elution pattern changes in order by the application of HIBA instead of MA and vice versa. Both HIBA and MA bind the metal ions through the same functional moieties but differ in their side-chains.…”

Synthesis, structures and optical properties of mononuclear La, Eu and Tb complexes supported by calix[4]arene ligands bearing three pendant salicylaldiminato arms

“…[10] The coordination chemistry of doubly [11,12] and quadruply substituted calix [4]arenes has been extensively investigated. [13][14][15][16][17] Much less is known about the lanthanide coordination chemistry of singly [18] or triply [19] functionalized calix [4]arenes, presumably due to more complicated synthetic procedures.…”