A study of anion binding behaviour of 1,3-alternate thiacalix[4]arene-based receptors bearing urea moieties

Three novel thiacalix[4]arene receptors 4a-c each with a 1,3-alternate conformation and possessing two urea moieties linking various phenyl groups substituted with either para electron-donating or -withdrawing groups have been synthesized. The binding properties of these receptors were investigated by means of 1H NMR spectroscopy and UV-vis absorption titration experiments using various anions. The structures and complexation energies were also studied by density functional theory (DFT) methods. The results suggested that receptor 4c, which possesses two p-(trifluoromethyl)phenyl ureido moieties, can complex most efficiently in the urea cavity and exhibits high selectivity towards F- and AcO- ions.