Large blue shift of the H–Ar stretching frequency in hydrogen- and halogen-bonded complexes of HArF with dihalogen molecules

Quantum chemical calculations have been performed on the complexes formed between HArF and dihalogen molecules (XY = ClCl, ClF, BrCl, and BrF) at the MP2/6-311++G(2d,2p) level. For each complex, two minima were found, which correspond to one hydrogen-bonded complex and one halogen-bonded complex. The halogen-bonded complex with the F atom of HArF is more stable than the hydrogen-bonded complex with the H atom of HArF. A large blue shift of the H–Ar stretching frequency was observed in the hydrogen-bonded complex. However, in the halogen-bonded complex, in which the H–Ar bond is not involved in the interaction, a much large blue shift was observed for the same bond. The natural bond orbital and atoms in molecules analyses have been performed for these complexes. The energy decomposition analysis indicated that the electrostatic interaction plays a main contribution in formation of both complexes although the contribution from the charge-transfer interaction is also important.