Synthesis of a tweezer-like bis(arylthiaalkoxy)calix[4]arene as a cation sensor for ion-selective electrodes: an investigation of the influence of neighboring halogen atoms on cation selectivity

Abstract

Two novel tweezer-like 25,27-dihydroxy-26,28-bis(phenylthiaethoxy)calix[4]arenes 6 and 7 were synthesized by the reaction of 25,27-dihydroxy-26,28-bis(bromoethoxy)calix[4]arenes 3 and 4 for the evaluation of their ion-selectivity in ion-selective electrodes (ISEs). X-ray structural analysis indicated that calix[4]arene 7 is in an interesting infinite linear aggregate via self-inclusion. For investigation of the influences of substitutes on the behavior of the ISEs, the halogen substituted aryl analogues of 25,27-dihydroxy-26,28-bis(arylthiaethoxy)calix[4]arenes 8–12 were also synthesized and their ISE performances were evaluated under the same conditions. ISEs based on 6–12 as neutral ionophores were prepared, and their selectivity coefficients for Ag⁺ (log K^pot_Ag,M) were investigated against other alkali metal, alkaline-earth metal, lead, ammonium ions and some transition metal ions using the fixed interference method (FIM). These ISEs showed excellent Ag⁺ selectivity over most of the interfering cations examined, except for Hg²⁺ having relative smaller interference (log K^pot_Ag,Hg ≤ 2.1). The ¹⁹F NMR spectra of 9 and 9·AgClO₄ were recorded for investigation the fluorine environments in the complex. The ¹⁹F NMR spectra strongly suggested that the fluorine atoms on ionophore 9 participated in ligation with silver cation.