Surprising enhancing effect of methyl group on the strength of O?XF and S?XF (X=Cl and Br) halogen bonds

摘要

The role of methyl group in H_2 O?XF and H_2 S?XF (X=Cl and Br) halogen-bonded complexes has been investigated with quantum chemical calculations. The halogen bond in the H_2 O?XF complexes is stronger than that in the H_2 S?XF complexes. However, the SX halogen bond is stronger than the OX one with the increase of methyl number. The result shows that the methyl group in the halogen acceptor has a positive contribution to the formation of halogen bond and there is a positive nonadditivity of methyl groups. Surprisingly, the methyl groups in dimethyl sulfide causes an increase of 150% for the interaction energy of SCl halogen bond. The natural bond orbital analyses have been performed to unveil the mechanism of the methyl group in the halogen bonding formation.