Recognition of anions through the combination of halogen and hydrogen bonding: A theoretical study

Anion recognition by the combination of different kinds of intermolecular forces has been evidenced in recent years. In this work, the binding behaviors of three urea-based receptors 1–3 towards several anions (Cl−, Br−, I−, NO 3 - ) have been investigated using density functional theory calculations. Distinct noncovalent interactions, involving halogen bonding, hydrogen bonding, and anion–π interactions, in the host–guest complexes under study are characterized. For the iodide receptor 1 composed of halogen- and hydrogen-bond donor groups (CI and NH), the anions are held by bidentate halogen and hydrogen bonds, while NH⋯anion and anion–π interactions are presented in the complexes of the perfluorinated receptor 2. On the other hand, multiple hydrogen bonding interactions (NH/CH⋯anion) occur between the host benzoate ester 3 and anionic guests. The introduction of iodine atoms into the phenyl groups of the receptor also leads to highly improved binding affinity of anions. The results presented here would provide a basis for the design and synthesis of new and functional host molecules exhibiting specific anion recognition.