Nature of the Hydrogen Bond Enhanced Halogen Bond

The factors responsible for the enhancement of the halogen bond by an adjacent hydrogen bond have been quantitatively explored by means of state-of-the-art computational methods. It is found that the strength of a halogen bond is enhanced by ca. 3 kcal/mol when the halogen donor simultaneously operates as a halogen bond donor and a hydrogen bond acceptor. This enhancement is the result of both stronger electrostatic and orbital interactions between the XB donor and the XB acceptor, which indicates a significant degree of covalency in these halogen bonds. In addition, the halogen bond strength can be easily tuned by modifying the electron density of the aryl group of the XB donor as well as the acidity of the hydrogen atoms responsible for the hydrogen bond.

Automated summary

The study revealed that the strength of a halogen bond is enhanced by approximately 3 kcal/mol when the halogen donor serves as both a halogen bond donor and a hydrogen bond acceptor. This enhancement is attributed to stronger electrostatic and orbital interactions between the XB donor and acceptor, indicating a significant level of covalency in these bonds. Furthermore, the halogen bond strength can be easily adjusted by altering the electron density of the aryl group of the XB donor and the acidity of the hydrogen atoms involved in the hydrogen bond.