Intermolecular Interactions and the Weak Benzene–Halogen Complexes

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Abstract
We have calculated the interaction potential between benzene and halogen molecules as a function of intermolecular distance for approach of the halogens along the sixfold axis of benzene. The calculations were based upon the perturbation theory developed by Murrell and co‐workers for intermolecular interactions in the region of small overlap. Emphasis was placed on the Coulombic and exchange terms. The former were calculated by numerical integrations over charge distributions developed from Slater‐type atomic orbitals. The exchange interaction was expanded on the basis of determinantal wavefunctions for each molecule, using approximate self‐consistent‐field molecular orbitals. The dispersion and induction energies were calculated using approximations common to long‐range theory. The charge‐transfer resonance interaction was estimated semiempirically. Both the stabilization energies and the equilibrium separations obtained for the Cl2, Br2, and I2 complexes were reasonable in comparison with experimental data. It was concluded that all interaction terms must be considered in the over‐all picture. If any one term can be singled out as playing a minor role in complex formation, it must be the charge‐transfer interaction. Since it was the only repulsive term calculated, the exchange interaction is extremely important in determining the geometry and stability of complexes.

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