Comparisons of the halogen-bonded and hydrogen-bonded complexes of furan, thiophene and pyridine with Lewis acids (ClF, HCl)

The geometries, interaction energies, tautomerization processes, electron density and Laplacian properties of the weak interaction systems formed by heteroaromatic rings (C4H4O, C4H4S and C5H5N) and Lewis acids (ClF, HCl) have been studied at the spin-restricted DFT method (X3LYP) with the aug-cc-pVTZ basis sets. Two types of interactions are observed among these systems: the σ-type and the π-type geometry. The low energy barriers (<2.3 kcal/mol) demonstrate that the σ-type and π-type angular geometries of C4H4O/C4H4S⋯ClF/HCl complexes are easily transformed from each other. The nature of the intramolecular interactions has been also investigated through both the theory of atoms in molecules (AIM) and energy decomposition analysis.