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: [[EQUATION]] = 121.0 and [[EQUATION]] = 70.0.