Bis(amido)calix[4]arenes in the pinched cone conformation as tuneable hydrogen-bonding anion receptors

Abstract

Calix[4]arene units functionalized at the 1,3-positions of the upper rim with amido groups, –NHC(O)X, act as neutral, hydrogen-bonding receptors for hydrogen sulfate, dihydrogen phosphate, acetate, benzoate, nicotinate, oxalate, terephthalate, isophthalate and fumarate with binding strength and selectivity tunable by varying the electron-withdrawing ability of the terminal substituent X (X = CH ₂ Cl, CHCl ₂ , CCl ₃ ).