Electrochemical Studies for Cation Recognition with Diazo-Coupled Calix[4]arenes

Abstract

The electrochemical properties of diazophenylcalix[4]arenes bearingortho-carboxyl group (o-CAC) andortho-ester group (o-EAC), respectively, in the presence of various metal ions were investigated by voltammetry in CH3CN.o-CAC ando-EAC showed voltammetric changes toward divalent metal ions and no significant changes with monovalent alkali metal ions. However,o-CAC preferentially binds with alkaline earth and transition metal ions, whereas no significant changes in voltammetric signals are observed ino-EAC with alkaline earth metal ions.o-EAC only binds with other transition metal ions. This can be explained on metal ion complexation-induced release of proton from the azophenol to the quinone-hydrazone tautomer followed by internal complexation of the metal ion with aid of nitrogen atoms andortho-carbonyl groups in the diazophenylazocalix[4]arenes.