C₃‐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 1H 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.