title: Origin of the X-Hal (Hal = Cl, Br) bond-length change in the halogen-bonded complexes.
abstract: The origin of the X-Hal bond-length change in the halogen bond of the X-Hal...Y type has been investigated at the MP2(full)/6-311++G(d,p) level of theory using a natural bond orbital analysis, atoms in molecules procedure, and electrostatic potential fitting methods. Our results have clearly shown that various theories explaining the nature of the hydrogen bond cannot be applied to explain the origin of the X-Hal bond-length change in the halogen bond. We provide a new explanation for this change. The elongation of the X-Hal bond length is caused by the electron-density transfer to the X-Hal sigma* antibonding orbital. For the blue-shifting halogen bond, the electron-density transfer to the X-Hal sigma* antibonding orbital is only of minor importance; it is the electrostatic attractive interaction that causes the X-Hal bond contraction.
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nAm. 2, 166 10 Prague 6, Czech Republic.
authors.forename: Weizhou
authors.initials: W
authors.lastname: Wang
authors.forename: Pavel
authors.initials: P
authors.lastname: Hobza
mesh_terms: D019281:Dimerization; D006219:Halogens / Q000737:chemistry*; D006860:Hydrogen Bonding; D011522:Protons; D014732:Vibration
chemical_list: D006219:Halogens; D011522:Protons