Abstract:

A theoretical study of the charge-transfer complexes(CTC), as defined by Mulliken, formed by benzene and dihalogen molecules X₂(X=F, Cl, Br, I) was carried out with second-order Møller-Plesset perturbation(MP2). In the global minimum of C₆H₆-X₂(X= F, Cl, Br, I), the halogen molecule is located above one of the C-C bond centers of benzene, and the halogen molecule bond axis also slightly tilts towards the axis perpendicular to the plane of the benzene ring. The natural bond orbital(NBO) analysis reveals that the number of charge-transfer is negligible for these charge-transfer complexes. Symmetry-adapted perturbation theory(SAPT) results show that the contribution of electrostatic effects to halogen bonding interactions is relatively small, and generally accounts for about 20% of the attractive interaction for the four complexes. Halogen bonding interaction in C₆H₆-F₂ system is principally dispersive in nature. The halogen bonds containing chlorine, bromine and iodine are largely dependent on the induction type interactions. And, interestingly, more induction(and less dispersive) interaction appears from F to I. The so-called "charge-transfer complexes(CTC)" for C₆H₆-X₂ system is not exact on electron correlation level.

Key words: Charge-transfer complex(CTC), Benzene(C₆H₆), Dihalogens molecule(X₂), Intermolecular interaction, Symmetry-adapted perturbation theory(SAPT)