Tri-ionizable calix[4]arene ligands: synthesis and lanthanide ion complexation

Abstract

New proton-ionizable p-tert-butylcalix-4-arene ligands with three N-(X)sulfonyl oxyacetamide groups and one methoxy group on the lower rim capable of forming electroneutral complexes with trivalent lanthanide ions are synthesized. Variation of the electron-withdrawing ability of X (Me, Ph, C6H4-4-NO2, CF3) is used to tune the ligand acidity. Conformations of the ligands in CDCl3 are investigated by variable temperature NMR spectroscopy. By potentiometric titration, complexation of La3+, Eu3+, and Yb3+ by the tri-ionizable complexing agents in MeOH is probed.