How does halogen bonding behave in solution? A theoretical study using implicit solvation model.

A systematic study of halogen bonding interactions in gas phase and in solution was carried out by means of quantum chemical DFT/B3LYP method. Three solvents with different polarities (chloroform, acetone, and water) were selected, and solvation effects were considered using the polarized continuum model (PCM). For charged halogen-bonded complexes, the strength of the interactions tends to significantly weaken in solution, with a concomitant elongation of intermolecular distances. For neutral systems, halogen bond distances are shown to shorten and the interaction energies change slightly. Computations also reveal that in the gas phase the binding affinities decrease in the order Cl(-) > Br(-) > I(-), while in solution the energy gaps of binding appear limited for the three halide anions. According to free energy results, many systems under investigation are stable in solution. Particularly, calculated free energies of formation of the complexes correlate well with halogen-bonding association constants determined experimentally. The differences of the effects of solvent upon halogen and hydrogen bonding were also elucidated. This study can establish fundamental characteristics of halogen bonding in media, which would be very helpful for applying this noncovalent interaction in medicinal chemistry and material design.