The halogen bond: an interim perspective

Abstract

There has been an upsurge of interest in the halogen bond during the last decade. This non-covalent interaction is less familiar than the hydrogen bond, but is similar to it in several respects. In this article, we first discuss the nature of the halogen bond in the gas phase, as established by systematic investigations of the rotational spectra of complexes B...XY, where B is a simple Lewis base and XY is a dihalogen molecule. The geometry of a given B...XY is found to be isomorphic with that of the corresponding hydrogen-bonded system B...HX, an observation that leads an interim definition of the halogen bond similar to that recently proposed for the hydrogen bond. Selected novel applications of the halogen bond made in the last decade in various areas of chemistry/materials (namely crystal engineering, liquid crystals, nano-materials, polymer chemistry and inorganic chemistry) are then reviewed. These applications generally involve molecules of the type XR (where R is an electron-withdrawing group) acting as the electron donor, rather than dihalogens XY.

The shape of the halogen atom—anisotropy of electron distribution and its dependence on basis set and method used

“…This partial positive charge on the valence sphere of the halogen atom is often defined within the framework of NBO theory [21] as a sigma hole-a local deficit of an electron charge (a hole) being placed opposite the sigma bond [22,23]. The sigma hole may interact with the local electron charge surplus such as lone electron pairs [17,24,25], pi-type electrons [17,24,26], or even sigma-type electrons [27]; in this way, the mechanism of formation of X-bond can be well defined. However, there are some discrepancies regarding the nature of X-bonding.…”

Communication: Competition between π⋯π interaction and halogen bond in solution: A combined 13C NMR and density functional theory study

“…The hydrogen bond is probably the most important noncovalent bond. 1,2 Other important noncovalent driving forces for supramolecular assembly include π · · ·π stacking interaction, [3][4][5][6][7][8][9][10][11][12][13] halogen bond, [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] etc. Noncovalent bonds are much weaker than the covalent bonds.…”

Halogen Bonding in Crystal Engineering

“…Probably the most commonly used halogen bonding acceptors are covalently bonded halogens and nitrogen atoms. [8,11,[20][21][22][23][24] Metal halides, oxygen, sulfur, selenium and even silicon have, however, been reported to have the capacity to act as halogen bond acceptors with suitable donors. [25][26][27][28][29][30][31] …”

“…This is again the result of the polarizability of the halogens increasing in the same series. [20] The bond strength can be increased further by substituting the second halogen atom in dihalogens with fluorine, which polarizes the other halogen even more strongly. [56,57] The lighter dihalogens are volatile and so the crystal structures of such systems are rather rare.…”