Synthesis and anion coordination chemistry of new calix[4]arene pyridinium receptors

New lower rim substituted calix[4]arene bis-pyridinium receptors L-1, L-2 and a novel lower rim bridged calix[4]arene pyridinium receptor L-3 have been prepared and shown to bind a variety of anionic guest species. Proton NMR titration studies in deuteriated DMSO solutions reveal L-1 and L-2 to complex H2PO4-, Cl-, Br-, HSO4- anions with L:2X(-) stoichiometry with L-1 exhibiting a selectivity preference for H2PO4-. L-3 forms 1:1 stoichiometric complexes with Cl- and Br- of similar stability. Cyclic voltammetric investigations have demonstrated L-1 to electrochemically recognise H2PO4- and Cl- anions.