A theoretical study on halogen-π interactions: X-C2-Y…C8H8 complexes

M06-2X functional was employed to study halogen-π interactions in X-C2-Y…C8H8 complexes (X, Y=H, F, Cl, and Br). In fact, interactions of mono- or di-halogenated acetylenes and planar cyclooctatetraene as an anti-aromatic π system were considered. Relationship between binding energies of the complexes and charge transfer effects was investigated. Also, electronic charge density values were calculated using atoms in molecules (AIM) method to connect properties of bond, ring, and cage critical points (BCPs, RCPs, and CCPs) to binding energies of the mentioned complexes. Size of halogen atoms has a role on strength of halogen-π interactions. Decrease of electronic charge density values at BCPs and CCPs of the complexes and increase of alteration of these values at RCPs is relatively consistent with increase of binding energies. Electron-withdrawing nature of Br atom leads to inverse charge transfer in some complexes. Description of halogen-π interactions on an anti-aromatic ring help to design new molecular systems with unique properties for crystal engineering.