New Neutral Receptors for Fluoride Based on Calix[4]arene Bearing Thiourea and Amide

Abstract

Two-armed neutral anion receptors (4, 5), calix[4]arenes bearing thiourea and amide binding sites, were prepared and examined their anion-binding ability by the UV-vis spectra. The results of non-linear curve fitting and Job plot indicate that 4 or 5 forms 1:1 stoichiometry complex with fluoride by hydrogen bonding interactions. Receptors 4 and 5 have an excellent selectivity for fluoride but have no binding ability with acetate, dihydrogen phosphate and the halogen anions (Cl-, Br-, I-).