No abstract

A multiple diglycolamide (DGA)-containing ligand having four DGA arms tethered to a tetraaza-12-crown-4 ring, viz. 2, 2′,2′′,2′′′-(((1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetrakis(2-oxoethane-2,1-diyl)) tetrakis (oxy)) tetrakis(N,N-dioctylacetamide) (T12C4ODGA), was synthesized and evaluated for the extraction of different actinide and lanthanide ions, viz. Am 3+ , Eu 3+ , Pu 4+ , Np 4+ , and UO 2 2+ . The extraction efficiency of the present ligand was found to be the highest reported so far, more specifically for the trivalent metal ions Am 3+ and Eu 3+ , when one considers the very low ligand concentration used in the present study, compared to that of the various previously reported multiple DGA-based ligands. The nature of the complexes formed during the extraction of Eu 3+ was investigated using time-resolved fluorescence (TRFS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Both the solvent extraction and TRFS studies indicated the presence of 1:1 and 1:2 complexes during the extraction of Am 3+ and Eu 3+ having three inner-sphere water molecules in the 1:1 complex. Density functional theoretical (DFT) studies were performed on the Am 3+ and Eu 3+ complexes of both T12C4ODGA and an analogous compound having methyl groups in place of the n-octyl groups, and the DFT results of the T12C4ODGA nicely explain the extraction behavior of Am 3+ and Eu 3+ .

N,N,N′,N′,N“,N”‐hexaalkylnitrilotriacetoamide (HRNTA) derivatives were found to be promising for the separation of trivalent actinides from lanthanides, which is a burning topic in the back end of the nuclear fuel cycle. In the present work, separation of Am3+ from Eu3+ was studied using the N,N,N’,N’,N’’,N’’‐hexa‐2‐ethylhexylnitrilotriacetamide (H2EHNTA) derivative and the role of the diluent medium to control the extractable complex was demonstrated. The effect of alkyl chain length and branching in the alkyl chain of different HRNTA (R=methyl, n‐butyl, n‐hexyl, n‐dodecyl and 2‐ethylhexyl) derivatives on their complexation with Eu3+ were investigated using steady‐state and time‐resolved luminescence studies. Different species formed at different ligand to metal ratios were identified from the luminescence titration experiments and their lifetime values measured. The experimental results were corroborated with the help of density functional theoretical (DFT) calculations on Am3+ and Eu3+ complexes of HRNTA derivatives with varying alkyl chain length and branching.

A novel tripodal diglycolamide ligand containing a triazamacrocycle center (2,2′,2′′-(((1,4,7-triazonane-1,4,7-triyl)­tris­(2-oxoethane-2,1-diyl)) tris­(oxy)) tris­(N,N-dioctylacetamide), abbreviated as T9C3ODGA) was synthesized and characterized by conventional techniques. The ligand resulted in efficient extraction of actinide/lanthanide ions yielding the trend: Eu3+ > Pu4+ > Am3+ > NpO2 2+ > UO2 2+ > Sr2+ > Cs+. Similar to most of the other diglycolamide (DGA) ligands, Eu3+ was preferentially extracted as compared to Am3+; the separation factor (D Eu/D Am) value at 3 M HNO3 was ca. 4.2. In contrast, separation from UO2 2+ ion was less effective as compared to that of other tripodal DGA ligands studied earlier. Solvent extraction studies indicated extraction of species of the ML2 (where L is T9C3ODGA) stoichiometry. The formation of an inclusion complex with no inner-sphere water molecule was confirmed from luminescence spectral studies. DFT computations predicted the presence of an inner-sphere nitrate ion in the most preferred complex, which was also supplemented by EXAFS and luminescence studies. The selectivity of T9C3ODGA could be explained on the basis of its more favorable interactions with Eu3+ as compared to those with Am3+ both in the gas and the solution phases.