, Volume 13, Issue 2, pp 305-311
Date: 30 Sep 2006

An overview of halogen bonding

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Halogen bonding (XB) is a type of noncovalent interaction between a halogen atom X in one molecule and a negative site in another. X can be chlorine, bromine or iodine. The strength of the interaction increases in the order Clsp hybridization of the s unshared electrons of X. The high electronegativity of fluorine and its tendency to undergo significant sp hybridization account for its failure to halogen bond. Some computed XB interaction energies are presented and discussed. Mention is also made of the importance of halogen bonding in biological systems and processes, and in crystal engineering.


The computed B3PW91/6-31G(d,p) electrostatic potential, in kcal mol−1, on the 0.001 electrons/bohr3 surface of NC–C≡C–Cl. The chlorine atom is at the right. The color ranges are: red, more positive than 15; yellow between 7 and 15; green, between 0 and 7; blue, between −10 and 0; purple, more positive than −10.

Proceedings of “Modeling Interactions in Biomolecules II”, Prague, September 5th–9th, 2005.