On the difference of the properties between the blue-shifting halogen bond and the blue-shifting hydrogen bond.

The difference of the properties between the blue-shifting halogen bond and the blue-shifitng hydrogen bond has been investigated at the M06/6-311++G(d,p) theory level. It was found that the three lone electron pairs on the halogen atom play an important role for the difference of the properties between the blue-shifting halogen bond and the blue-shifitng hydrogen bond. The additional electron-density transfer from the three lone electron pairs on the halogen atom to the remote part of the halogen atom donor (i.e., the antibonding orbitals of the bonds other than X-Hal) makes the blue-shifting halogen bond much more ubiquitous in the halogen-bonded complexes than the blue-shifitng hydrogen bond in the hydrogen-bonded complexes, and it also makes the values of the X-Hal bond contraction generally much larger than the values of the X-H bond contraction. The difference of the properties between the X-Cl...Y blue-shifting halogen bond and the X-Br...Y blue-shifting halogen bond was also discussed.