Characteristics and nature of the intermolecular interactions between thiophene and XY(X, YÂ =Â F, Cl, Br): A theoretical study

The characteristics (equilibrium geometries, interaction energies, charge transfer and orbital interactions) of the intermolecular interactions in complexes thiophene-XY(X, Y = F, Cl, Br) are examined at the second-order Møller-Plesset (MP2) level. For each complex, three types of intermolecular interactions (π-halogen bonded, σ-halogen bonded and hydrogen bonded) are observed and the π-halogen bonded interaction is the most stable one. The NBO (natural bond orbital) analysis demonstrates that the charge transfer is important in the π-halogen bonded interaction and the main stabilization energy is due to the σ(C2-C3) → σ∗(X-Y) orbital interaction. To further study the nature of the intermolecular interactions, an SAPT (the symmetry adapted perturbation theory) energy decomposition analysis was carried out and the results indicate that both the π-halogen bonded and σ-halogen bonded interactions are predominantly inductive energy in nature, while dispersion energy dominates the hydrogen bonded interactions.