Synthesis and cations complexation of dumbbell shaped biscalix[4]-1,3-aza-crown with rigid thiourea-bridge

Abstract

By reacting calix[4]-1,3-aza-crown 2 with 1,4-phenyl diisothiocyanate in “1 + 2” condensation mode, the novel dumbbell shaped biscalix[4]-1,3-aza-crown 3 with rigid thiourea-bridge was conveniently prepared in yield of 85%. Its structure and conformation were characterized by elemental analyses, ESI-MS, 1H NMR and 1H–1H COSY techniques. The complexation properties of compound 3 were investigated by liquid–liquid extraction experiments and 1H NMR titration experiments. The results showed that compound 3 has excellent complexation abilities for soft cations and outstanding extraction selectivity for Ag+. The Ag+/Na+ and Ag+/Hg2+ extraction percentage of host 7 were as high as 43.2 and 16.9, respectively. 1H NMR titration experiments revealed the 1:2 stoichiometry of receptor 3-Ag+ complex was formed.