A novel calix[4]arene-based neutral semicarbazone receptor for anion recognition

A series of novel calix[4]arene-based neutral semicarbazone and thiosemicarbazone receptors have been synthesized and characterized. The molecular receptor 4a recognizes HSO4- in preference to other anions (Cl−, Br−, I−, ClO4-, H2PO4- and PF6-) through a 1:1 binding-stoichiometry.