Shape Selective Anion Recognition of Calix[4]resorcinarene-Based Receptors through C—H Hydrogen Bonding

Abstract

This study explores the synthesis of calix[4]resorcinarene-based anion receptors and their shape selective recognition properties. Electron withdrawing groups are modified at the bridging site of the resorcinarene scaffold, leading to a reduction in the electron density of the receptors. The number of fluorine atoms in the receptors is adjusted to regulate their ability to bind anions. Our results demonstrate that these receptors bind with anions in two manners: electropositive "H" atoms in the concave cavity bind with non-spherical anion [MeSO₃]⁻ and the lower "crown" binds with spherical anion [Cl]⁻. The two binding modes are both driven by C—H∙∙∙anion hydrogen bonding. Besides, mass spectrometric experiments and density functional theory (DFT) calculations also verified the binding mechanism.