Tetra-Substituted p-Tert-Butylcalix[4]Arene with Phosphoryl and Salicylamide Functional Groups: Synthesis, Complexation and Selective Extraction of f-Element Cations.

A new series of lanthanide (1-5) and uranyl (6) complexes with a tetra-substituted bifunctional calixarene ligand H2 L is described. The coordination environment for the Ln3+ and UO2 2+ ions is provided by phosphoryl and salicylamide functional groups appended to the lower rim of the p-tert-butylcalix[4]arene scaffold. Ligand interactions with lanthanide cations (light: La3+ , Pr3+ ; intermediate: Eu3+ and Gd3+ ; and heavy: Yb3+ ), as well as the uranyl cation (UO2 2+ ) is examined in the solution and solid state, respectively with spectrophotometric titration and single crystal X-ray diffractometry. The ligand is fully deprotonated in the complexation of trivalent lanthanide ions forming di-cationic complexes 2 : 2 M : L, [Ln2 (L)2 (H2 O)]2+ (1-5), in solution, whereas uranyl formed a 1 : 1 M : L complex [UO2 (L)(MeOH)]∞ (6) that demonstrated very limited solubility in 12 organic solvents. Solvent extraction behaviour is examined for cation selectivity and extraction efficiency. H2 L was found to be an effective extracting agent for UO2 2+ over La3+ and Yb3+ cations. The separation factors at pH 6.0 are: ßUO 2 2 + /La 3 + =121.0 and ßUO 2 2 + /Yb 3 + =70.0.