Theoretical study on O⋯Br and O⋯Cl halogen bonds in some small model molecular systems

Abstract

Halogen bonding interactions of type X⋯O=C are important in various fields including biological systems. In this work, theoretical calculations were carried out using B3LYP/6-31 ++G**, MP2/6-31 ++G** and MP2/aug-cc-pVDZ methods on a series of O⋯X halogen bonds between CH2O and CH3CHO as halogen bond acceptor with X-Y (X = Cl, Br; Y = CF3, CF2H, CFH2, CN, CCH, CCCN) as halogen bond donors. The strength of interaction energy for O⋯Br halogen-bonded complexes varies from −2.16 to −5.26 kcal/mol while for O⋯Cl complexes, it is between −1.65 to −3.67 kcal/mol, which indicate the O⋯Br bond to be stronger in comparison to O⋯Cl bond. SAPT analysis suggests that the strength of halogen bonding arises from the electrostatic and induction forces while dispersion is playing a comparatively smaller role. The halogen-bonded interaction energies were found to correlate well with positive electrostatic potential VS,max, halogen bonded distances, and the change in s-character of C-X bond. The halogen-bonded interaction energies were also evaluated for O⋯I bonded complexes and thus these complexes were found to be stronger than O⋯Br and O⋯Cl bonded complexes. Theoretical calculations were carried out on halogen bonded complexes CH2O⋯X-Y and CH3CHO⋯X-Y (X = Cl, Br, I; Y = CF3, CF2H, CFH2, CN, CCH, CCCN). The interaction energies increase in the order O⋯Cl < O⋯Br < O⋯I. The interaction energies were found to be correlate well with the VS,max, halogen bonded distances, and the change in s-character of C-X bond.