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

Halogen bonding interactions of type X center dot center dot center dot 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 center dot center dot center dot 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 center dot center dot center dot Br halogen-bonded complexes varies from -2.16 to -5.26 kcal/mol while for O center dot center dot center dot Cl complexes, it is between -1.65 to -3.67 kcal/mol, which indicate the O center dot center dot center dot Br bond to be stronger in comparison to O center dot center dot center dot 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 V-S,V-max, halogen bonded distances, and the change in s-character of C-X bond. The halogen-bonded interaction energies were also evaluated for O center dot center dot center dot I bonded complexes and thus these complexes were found to be stronger than O center dot center dot center dot Br and O center dot center dot center dot Cl bonded complexes.