C-3-symmetric tripodal thio/diglycolamide-based ligands for trivalent f-element separations

Three new C-3 -symmetric ligands bearing diglycolamide and thiodiglycolamide units on a triphenoxymethane platform have been synthesized and evaluated as trivalent f-element extractants from nitric acid media. Liquid-liquid extraction studies of eleven different lanthanides from 1 M nitric acid into dichloromethane revealed a strong influence of the amidic substituents on the extraction efficiency. A comparison of the 1 H NMR spectrum of the Lu(III) complex formed with the tris-DGA ligand and the organic solution after the extraction experiment confirms that all three arms bind the metal during the extraction experiment and form a C 3 -symmetric complex. The newly synthesized lipophilic di-n-butyl tris-diglycolamide was found to be a significantly weaker extractant in comparison to the di-isopropyl analogs. The distance separating the metal binding groups from the triphenoxymethane platform had little influence on the selectivity or binding efficiency of the ligands. Experiments with the tris-thiodiglycolamide derivative highlighted the importance of the etheric oxygens for metal binding.