The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

Halogen bonding is the noncovalent interaction between halogen atoms (Lewis acids) and neutral or anionic Lewis bases. The main features of the interaction are given, and the close similarity with the hydrogen bonding will become apparent. Some heuristic principles are presented to develop a rational crystal engineering based on halogen bonding. The focus is on halogen-bonded supramolecular architectures given by halocarbons. The potential of the interaction is shown by useful applications in the field of synthetic chemistry, material science, and bioorganic chemistry.

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Halogen Bonding Based Recognition Processes: A World Parallel to Hydrogen Bonding †

Halogen bonding is the noncovalent interaction where halogen atoms function as electrophilic species. The energetic and geometrical features of the interaction are described along with the atomic characteristics that confer molecules with the specific ability to interact through this interaction. Halogen bonding has an impact on all research fields where the control of intermolecular recognition and self-assembly processes plays a key role. Some principles are presented for crystal engineering based on halogen-bonding interactions. The potential of the interaction is also shown by applications in liquid crystals, magnetic and conducting materials, and biological systems.

Halogen Bonding in Supramolecular Chemistry

A σ-hole bond is a noncovalent interaction between a covalently-bonded atom of Groups IV–VII and a negative site, e.g. a lone pair of a Lewis base or an anion. It involves a region of positive electrostatic potential, labeled a σ-hole, on the extension of one of the covalent bonds to the atom. The σ-hole is due to the anisotropy of the atom's charge distribution. Halogen bonding is a subset of σ-hole interactions. Their features and properties can be fully explained in terms of electrostatics and polarization plus dispersion. The strengths of the interactions generally correlate well with the magnitudes of the positive and negative electrostatic potentials of the σ-hole and the negative site. In certain instances, however, polarizabilities must be taken into account explicitly, as the polarization of the negative site reaches a level that can be viewed as a degree of dative sharing (coordinate covalence). In the gas phase, σ-hole interactions with neutral bases are often thermodynamically unfavorable due to the relatively large entropy loss upon complex formation.

Halogen bonding and other σ-hole interactions: a perspective

The halogen bonding in supramolecular chemistry

The spatial charge arrangement of a typical quasi-two-dimensional organic conductor alpha-(BEDT-TTF)2I3 is revealed by single crystal structure analysis using synchrotron radiation. The results show that the horizontal stripe type structure, which was suggested by mean field theory, is established. We also find the charge disproportion above the metal-insulator transition temperature and a significant change in transfer integrals caused by the phase transition. Our result elucidates the insulating phase of this material as a 2k_F charge density localization.

Charge Ordering in alpha-(BEDT-TTF)2I3 by synchrotron x-ray diffraction

Novel radical cation salts of organic π-donors containing iodine atom(s): the first application of strong intermolecular-I···X-(X = CN, halogen atom) interaction to molecular conductors

The novel molecular conductors, (DIETS)4M(CN)4(M = Ni, Pd, Pt) where reticulated donor-anion contacts are constructed using the strong and directional –-I ⋯ NC– interaction, are synthesized and characterized.

Novel molecular conductors, (DIETS)4M(CN)4(M = Ni, Pd, Pt): highly reticulated donor ⋯ anion contacts by –I ⋯ NC– interaction

Coexistence of one- and three-dimensional fermi surfaces and heavy cyclotron mass in the molecular conductor (dme-dcnqi)2cu

Preparation and physical properties of an alloyed (DMe-DCNQI)2Cu with fully deuterated DMe-DCNQI (DMe-DCNQI = 2,5-dimethyl- N,N′-dicyanoquinonediimine)

Hiroshi Sawa

Papers

Charge Ordering in alpha-(BEDT-TTF)2I3 by synchrotron x-ray diffraction

Novel radical cation salts of organic π-donors containing iodine atom(s): the first application of strong intermolecular-I···X-(X = CN, halogen atom) interaction to molecular conductors

Novel molecular conductors, (DIETS)4M(CN)4(M = Ni, Pd, Pt): highly reticulated donor ⋯ anion contacts by –I ⋯ NC– interaction

Coexistence of one- and three-dimensional fermi surfaces and heavy cyclotron mass in the molecular conductor (dme-dcnqi)2cu

Preparation and physical properties of an alloyed (DMe-DCNQI)2Cu with fully deuterated DMe-DCNQI (DMe-DCNQI = 2,5-dimethyl- N,N′-dicyanoquinonediimine)