Aza crown ether calix[4]arenes containing cation and anion binding sites: effects of metal ions towards anion binding ability

Abstract

Tripodal aza crown ether calix[4]arenes containing both cation and anion binding sites ( 5a and 5b ) have been synthesized. The X-ray analysis shows that 5a forms a self-threaded rotaxane-like structure in the solid state. 1H NMR titrations of the two ligands with various halide anions indicate that 5a and 5b can form complexes with Br − and I − but not F −. However, both compounds form more stable complexes with I − than with Br − in the presence of Bu 4N +. The presence of K + enhances the binding ability of 5a towards Br −.