A highly efficient neutral anion receptor in polar environments by synergy of anion−π interactions and hydrogen bonding

Abstract

Herein, it is shown how anion recognition in highly polar solvents by neutral metal-free receptors is feasible when multiple hydrogen bonding and anion−π interactions are suitably combined. A neutral aromatic molecular tweezer functionalized with azo groups is shown to merge these two kinds of interactions in a unique system and its efficiency as an anion catcher in water is evaluated using first-principles quantum methods. Theoretical calculations unequivocally prove the high thermodynamic stability in water of a model anion, bromide, captured within the tweezer’s cavity. Thus, static calculations indicate anion–tweezer interaction energies within the range of covalent or ionic bonds and stability constants in water of more than 10 orders of magnitude. First-principles molecular dynamics calculations also corroborate the stability through the time of the anion–tweezer complex in water. It shows that the anion is always found within the tweezer’s cavity due to the combination of the tweezer–anion interactions plus a hydrogen bond between the anion and a water molecule that is inside the tweezer’s cavity.