A theoretical study of substitution effects on halogen-π interactions

Ab initio calculations are performed to analyse the existence of intermolecular halogen center dot center dot center dot pi interactions in NCX complexes with YC equivalent to CY, where X = Cl, Br and Y = H, CN, F, Cl, OH, NH2, and CH3. Molecular geometries and interaction energies of the complexes are investigated at the MP2/aug-cc-pVTZ level of theory. Our results indicate that the interaction energies for the NCX center dot center dot center dot YC equivalent to CY complexes lie in the range between -0.5 and -5.9 kcal/mol. The physical nature of the interactions is studied using symmetry-adapted perturbation theory (SAPT). The stability of the X center dot center dot center dot pi interactions is predicted to be attributable mainly to electrostatic and dispersion effects.