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 H 2 L is described. The coordination environment for the Ln 3+ and UO 2 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: La 3+ , Pr 3+ ; intermediate: Eu 3+ and Gd 3+ ; and heavy: Yb 3+ ), as well as the uranyl cation (UO 2 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, [Ln 2 (L) 2 (H 2 O)] 2+ (1-5), in solution, whereas uranyl formed a 1 : 1 M : L complex [UO 2 (L)(MeOH)] ∞ (6) that demonstrated very limited solubility in 12 organic solvents. Solvent extraction behaviour is examined for cation selectivity and extraction efficiency. H 2 L was found to be an effective extracting agent for UO 2 2+ over La 3+ and Yb 3+ cations. The separation factors at pH 6.0 are: β UO 2 2 + /La 3 + =121.0 and β UO 2 2 + /Yb 3 + =70.0.