Anion recognition by phosphonium calix[4]arenes: synthesis and physico-chemical studies

p-tert-Butylcalix[4]arenes, in the cone conformation, di- and tetra-substituted at the narrow rim with charged phosphonium groups, have been synthesised and characterised. Their interactions with a wide range of anions have been investigated in chloroform and acetonitrile solutions by means of 1H and 31P NMR and isothermal titration microcalorimetry. These compounds have also been incorporated as sensing material in poly(vinyl chloride) ion-selective electrodes. The results showed that they interact strongly with the more lipophilic anions Cl[image omitted], SCN- and I-, in solution as in the electrode membranes. The origin of this selectivity is discussed and, in particular, the role of the salt counterion is examined.