1Department of Physical Chemistry, University of Tabriz, Tabriz, Iran
2Department of Chemistry, Kharazmi (Tarbiat Moallem) University, Tehran, Iran
The character of the intermolecular interactions in Cl2-HX (X =F, Cl and Br) complexes has been investigated by means of the second-order Möller–Plesset perturbation theory (MP2) and the density functional theory (DFT) calculations. The results show that there are two types of lowest interaction potential equilibrium structures in the interactions between Cl2 and HX: X∙∙∙Cl type geometry and hydrogen-bonded geometry. The calculated interaction energies show that the X∙∙∙Cl type structures are more stable than the corresponding hydrogen-bonded structures. The nature of the intermolecular interactions has been also investigated by natural bond orbital (NBO) and atoms in molecules (AIM). The AIM analysis reveals that both types of intermolecular interactions are “closed-shell” noncovalent interactions.