Chloride ion recognition using thiourea/urea based receptors incorporated into 1,3-disubstituted calix[4]arenes

New calix[4] arene derivatives (3-5, 7-8) of cone and 1,3-alternate conformations possessing thiourea/urea moieties have been synthesized and examined for their anion recognition abilities towards different anions like fluoride, chloride, bromide, iodide, nitrate and acetate by H-1 NMR and UV-Vis spectroscopy. Fitting the changes in the absorption spectra using nonlinear regression analysis indicates that all these compounds have strong binding affinity for chloride ions. The stoichiometry of the hydrogen bonded complexes is 1 : 1 (H : G) for receptor 3-5, while it is 2 : 1 (H : G) with 7-8. Chloride ion selective electrodes (ISEs) were also formed which showed excellent selectivity over all other anions tested.