Tris-phenylurea-substituted calixamides (3a, 3b) and tris-phenylthiourea-substituted calixamides (4a, 4b) were synthesised by the reaction of amine with isocyanates and thioisocyanate, respectively. Single crystal X-ray analysis revealed that the cyclic trimers adopt a syn conformation with all of the urea groups on the same side. The binding affinities of these compounds towards anions were measured using 1H NMR titrations in DMF-d7, DMSO-d6 or CDCl3. Each receptor was observed to bind halogen anions in a 1:1 stoichiometry, exclusively through hydrogen bonding, and the anion selectivity was in the order F- > Cl- ≫ Br- > I- . DFT calculations revealed that the fluoride anion is anchored in the centre of the six N-H hydrogen atoms of 3a through H...F interactions.
ASJC Scopus subject areas
- 化学 (全般)