Topological and metal ion effects on the anion binding abilities of new heteroditopic receptors derived from p-tert-butylcalix[4]arene

Two derivatives of p-tert-butylcalix[4]arenes 1 and 2 containing diethyl ester and amidoferrocene units as cation and anion binding sites, respectively, have been synthesized. Both compounds were isomeric with different topology for accommodating ions. 1H NMR spectroscopy, cyclic voltammetry, and square-wave voltammetry were used to study the binding abilities of receptors 1 and 2 toward anions. Both receptors were found to bind Br− and I− selectively in the presence of Na+. The electrochemically oxidized ferrocenium form of para-isomer 2 in the free form was found to sense AcO− selectively, but demonstrated a negative sensing in the presence of Na+. In contrast, the electrochemically oxidized ferrocenium form of meta-isomer 1 was found to enhance sensing of AcO− and Cl− in the presence of Na+.