Halogen Bonding: An Interim Discussion

Abstract

Halogen bonding is a noncovalent interaction that is receiving rapidly increasing attention because of its significance in biological systems and its importance in the design of new materials in a variety of areas, for example, electronics, nonlinear optical activity, and pharmaceuticals. The interactions can be understood in terms of electrostatics/polarization and dispersion; they involve a region of positive electrostatic potential on a covalently bonded halogen and a negative site, such as the lone pair of a Lewis base. The positive potential, labeled a σ hole, is on the extension of the covalent bond to the halogen, which accounts for the characteristic near-linearity of halogen bonding. In many instances, the lateral sides of the halogen have negative electrostatic potentials, allowing it to also interact favorably with positive sites. In this discussion, after looking at some of the experimental observations of halogen bonding, we address the origins of σ holes, the factors that govern the magnitudes of their electrostatic potentials, and the properties of the resulting complexes with negative sites. The relationship of halogen and hydrogen bonding is examined. We also point out that σ-hole interactions are not limited to halogens, but can also involve covalently bonded atoms of Groups IV-VI. Examples of applications in biological/medicinal chemistry and in crystal engineering are mentioned, taking note that halogen bonding can be "tuned" to fit various requirements, that is, strength of interaction, steric factors, and so forth.

On the opposite trends of correlations between interaction energies and electrostatic potentials of chlorinated and methylated amine complexes stabilized by halogen bond

“…It has been shown for several halogen-or chalcogenbonded complexes that the interaction energies correlate with the V s,max on a σ-hole donor. The bigger the V s,max , the bigger the values of the |ΔE| [24,[26][27][28]. Similar effect was obtained for the complexes studied in this work.…”

“…It is suggested that the increase in CT in the methylated amine complexes is associated with the weakening of negative hyperconjugation between LP(N) and trans antibonding σ*(CH) orbital(s). This effect is probably responsible for the negative acceptor (σ-hole donor) [24,[26][27][28]. The bigger the value of V s,max , the bigger the absolute value of the interaction energy.…”

RCH3···O Interactions in Biological Systems: Are They Trifurcated H-Bonds or Noncovalent Carbon Bonds?

“…For this reason, the correct description and understanding of noncovalent interactions between molecules is essential for being successful in this field of research. In general, strong and highly directional interactions, such as hydrogen bonding and σ-hole bonding [7][8][9][10][11][12][13][14][15][16][17], and less directional forces like ion pairing are used for this purpose.…”

“…electron acceptor) has been explored by Mani and Arunan [41]. They demonstrated that the carbon atom in fact could act as an electrophilic center which can non-covalently bond with electron-rich entities leading to noncovalent carbon bonding, following a nomenclature analogous to other σ-hole interactions [7][8][9][10][11][12][13][14][15][16][17]. The theoretical predictions were confirmed experimentally by Guru Row's group [42], thus validating the existence of this type of bonding by means of X-ray charge density analysis.…”

Intra-/Intermolecular Bifurcated Chalcogen Bonding in Crystal Structure of Thiazole/Thiadiazole Derived Binuclear (Diaminocarbene)PdII Complexes

“…The hydrogen [1,2], halogen [3][4][5][6][7][8][9][10], chalcogen [11][12][13][14][15][16][17][18][19][20][21][22][23][24], pnictogen [25][26][27][28][29][30][31], tetrel [32] bonding, stacking [33][34][35][36][37], cation/anion-π [38][39][40][41][42], and metallophilic interactions [43][44][45] play key roles in many chemical, physical, and biochemical processes, due to their ability to control structures and properties of associates and supramolecular systems.…”