Halogen bond

Halogen bond

A halogen bond is the noncovalent attractive interaction between an electron poor halogen atom (usually iodine or bromine) and an electron rich site such as that presented by a Lewis base.citeweb|url=http://www.rsc.org/delivery/_ArticleLinking/DisplayArticleForFree.cfm?doi=b605101d&JournalCode=CC|title=Fluorinated liquid crystals formed by halogen bonding|accessdate=2007-03-03] Halogen bonding refers only to the case in which halogen works as an electrophilic species. The various other non-covalent halogen interactions come under different terms, and are treated separately.

History

In the 1950s and 1960s Mulliken was carrying out work on the theory of electron donor-acceptor complexes. Further works were carried out in the same period by Hassel and his coworkers, this time using X-ray diffraction techniques to study the crystals of complexes formed by dihalogen molecules with Lewis bases. The results of this work lead Hassel to the conclusion that in complexes formed between electrophilic halogen species and Lewis bases, "halogen atoms are directly linked to donor atoms with a bond direction roughly coinciding with the axes of the orbitals of the lone pairs in the non-complexed donor molecule".

In the 1980s continued studies were carried out on isolated complexes using infrared spectroscopy. Fourier transform spectroscopy allowed complexes formed from simple Lewis bases and dihalogen molecules to be isolated and probed before they could undergo reaction.

Applications

Applications include liquid crystals, crystal engineering and many biological processes, like the binding of the thyroid hormone thyroxine at its transport proteins.citeweb|url=http://www.pnas.org/cgi/reprint/101/48/16789|title=Halogen bonds in biological molecules|accessdate=2007-11-22]

References

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