Benzene-centred tripodal diglycolamides for the sequestration of trivalent actinides: metal ion extraction and luminescence spectroscopic investigations in a room temperature ionic liquid

Abstract

Three benzene-centred tripodal diglycolamide (Bz-T-DGA) ligands, where the diglycolamide (DGA) moieties are attached to a central benzene ring through ethylene spacers (LI), amide groups (LII) or ether linkages (LIII), were evaluated for their extraction behaviour towards trivalent actinide and lanthanide ions in a room temperature ionic liquid (RTIL), viz. 1-butyl-3-methylimidazolium bis(trifluoromethane)sulfonimide ([Cmim][TfN]). The extraction behaviour of these ligands in [Cmim][TfN] medium was compared with that obtained in the molecular solvent n-dodecane showing an opposite selectivity of LIII > LII > LIvs. LI > LII > LIII. In contrast to the n-dodecane medium, where a solvation extraction mechanism prevailed, a cation exchange mechanism was found to be operative in the RTIL medium. The stoichiometry of the extracted Amcomplex was found to be 1 : 2 (metal/ligand) and a nitrate ion was absent in the extracted complex. The luminescence spectroscopy of the Eu/ligand extracted complexes in the [Cmim][TfN] phase confirmed the absence of water molecules and that all the primary coordination sites of the metal ion are occupied by the ligands. The ligands display very large Pu/U, Am/U and Eu/U separation factor in the RTIL medium.

Complexation and Separation of Trivalent Actinides and Lanthanides by a Novel DGA Derived from Macrocyclic Crown Ether: Synthesis, Extraction, and Spectroscopic and Density Functional Theory Studies

“…The influence of the ligand concentration on the extraction of Am­(III) and Eu­(III) is shown in Figure c; the logarithmic curve of D M and the concentration of the ligand has a straight slope of 1.76 and 1.82, indicating that Cr6DGA with Am­(III) and Eu­(III) mainly exist in a 2:1 extraction species, which is very similar to other DGAs. , …”

“…It can be predicted that the preattachment of three to four DGA molecules to a molecular platform will improve the affinity of the ligand to trivalent lanthanide and actinide ions, and this ligand may demonstrate a higher ability to extract trivalent lanthanide and actinide ions than TODGA. Therefore, some researchers have developed a series of multiple-DGA-functionalized ligands by attaching multiple DGA arms to a central platform to make the extraction process more thermodynamically favorable and independent of diluents, such as 2,2′-((9-methyl-9-(11-octyl-6,10-dioxo-2,8-dioxa-5,11-diazanonadecyl)-2,16-dioxo-7,11-dioxa-3,15-diazaheptadecane-1,17-diyl)­bis­(oxy))­bis­( N , N -dioctylacetamide) (T-DGA), 2,2′,2″-((((nitrilotris­(ethane-2,1-diyl))­tris­(azanediyl))­tris­(2-oxoethane-2,1-diyl))­tris­(oxy))­tris­( N , N -dioctylacetamide) (TREN-DGA), and 2,2′,2″-(((((2,4,6-triethylbenzene-1,3,5-triyl)­tris­(ethane-2,1-diyl))­tris­(azanediyl))­tris­(2-oxoethane-2,1-diyl))­tris­(oxy))­tris­( N , N -dioctylacetamide) (Bz-T-DGA), and the M/L ratio of the extracted species by these ligands is 1:2, and only one DGA unit in a multiple-DGA extractant molecule participates in the coordination and extraction of metal ions. − Recently, 2,2′,2″-(((1,4,7-triazonane-1,4,7-triyl)­tris­(2-oxoethane-2,1-diyl))­tris­(oxy))­tris­( N , N -dioctylacetamide) (T9C3ODGA, Figure ) was designed by connecting three DGA arms to the macrocyclic aza-crown ether to reduce the steric hindrance of the ligand and make full use of the advantages of multiple-DGA-functionalized structures, and the distribution ratios of Eu­(III)/Am­(III) by T9C3ODGA were significantly higher than those of T-DGA and TREN-DGA . Although the protonation of macrocyclic aza-crown ether occurs under strong acid conditions, the extraction experiments showed that the distribution ratio and the selectivity for Eu­(III)/Am­(III) are not significantly affected .…”

Role of diluent in the unusual extraction of Am3+ and Eu3+ ions with benzene-centered tripodal diglycolamides: local structure studies using luminescence spectroscopy and XAS

“…Amongst the tripodal ligands, benzene-centred tripodal diglycolamide (abbreviated as Benz-T-DGA) ligands have been found to be highly efficient for the extraction of the trivalent Ln 3+ /An 3+ ions. 26,29,30 Previously, we have reported the interesting separation behaviour of Am 3+ and Eu 3+ ions with the Benz-T-DGA ligands L I and L II 26 (Fig. 2).…”

“…As the reverse micelle or 'self-assembly' formation requires the diluent to be non-polar, the whole phenomenon is controlled by the choice of diluent. This has been amply exploited by synthesizing DGA-functionalized calix [4]arenes, 23 or tripodals, 3,[24][25][26][27][28][29] which indeed gave very high extraction efficiencies for lanthanide and trivalent actinide ions. Amongst the tripodal ligands, benzene-centred tripodal diglycolamide (abbreviated as Benz-T-DGA) ligands have been found to be highly efficient for the extraction of the trivalent Ln 3+ /An 3+ ions.…”

Synergistic Enhancement of the Extraction and Separation Efficiencies of Lanthanoid(III) Ions by the Formation of Charged Adducts in an Ionic Liquid

“…The IL-based two-phase system has been widely investigated for the extraction of metal ions, such as rare earth elements and actinoids. − In the IL extraction systems, cationic and anionic species can also be extracted into the IL phase through a unique ion-exchange process. − For example, the ion-exchange extraction of anionic metal complexes has been observed by using an acidic chelating reagent, such as 2-thenoyltrifluoroacetone (Htta; Figure ). − The cation- and anion-exchange mechanisms are specific to the IL extraction systems, often leading to enhanced extractability and separability of Ln­(III) and other metal ions.…”