Highly Efficient Extraction of Trivalent f ‐Cations Using Several N ‐Pivot Tripodal Diglycolamide Ligands in an Ionic Liquid: The Role of Ligand Structure on Metal Ion Complexation

Complexation of trivalent lanthanides and actinides was studied in a room temperature ionic liquid (RTIL) using five N ‐pivot tripodal diglycolamide ligands ( L I – L V ) having different structural features, viz. spacer lengths and substituents. The nature of the metal/Ligand complex changed with the substitution of N atom near the tripodal platform from ML with L III and L IV to ML 2 with L I , L II and L V (where M = Eu 3+ /Nd 3+ /Am 3+ ). With 0.2 mmol/L ligands, the distribution ratio of Am 3+ at 1 m HNO 3 followed the order: L I (210) > L II (42) > L III (2.1) > L V (0.7) > L IV (0.2). The formation constants between Nd 3+ and the ligands (log  β ML,ML 2 ) followed an identical order, viz. L I > L II > L III > L V > L IV . The extraction of Am 3+ or Eu 3+ with all the ligands followed a cation‐exchange extraction mechanism, which is in sharp contrast to the results obtained in a molecular solvent ( n ‐dodecane), where a solvation extraction mechanism prevalied. Luminescence studies on the Eu 3+ extract in RTIL confimed the absence of water molecules in the inner coordination sphere of the complex. EXAFS studies indicated that all three DGA arms were binding to the Eu 3+ cation.