Halogen bonding and other σ-hole interactions: a perspective

Abstract

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.

Close contacts involving germanium and tin in crystal structures: experimental evidence of tetrel bonds

“…σ-Hole interactions [10][11][12] represent a relatively recent entry into the canon of weak bonds [13][14][15], but following the seminal papers of P. Politzer et al [16,17], these interactions rapidly became popular targets for studies in this field [15,[18][19][20]. A covalently bonded atom characteristically has a region of low electron density, known as the Bσ-hole,ŵ hich is usually located along the extension of the covalent bond but on the opposite side of the atom to the bond.…”

“…In general, the largest number of σ-holes that an atom can have (which may drive the formation of attractive interactions) is equal to the number of the covalent bonds it is involved in. The more electron-withdrawing the group(s) covalently bound to a given atom is/are, the more extended and more positive the σ-hole(s) opposite to the bond(s) is/are [21], and the stronger and shorter the resulting σ-hole interaction(s) is/are. A distinctive feature of σ-hole interactions is their directionality, a consequence of the rather localized nature of the region(s) of positive electrostatic potential.…”

Charge-assisted N(+)–H···(−)S hydrogen bonds in the crystal structure of selected diammonium thiophenolates

“…The continua overlap with stretching vibration of aromatic C-H at 3100-3000 cm -1 and C-H stretching present in diamines molecules at 3000-2850 cm -1 , as well as the very weak stretching bands of the S-H bonds usually registered 2600-2550 cm -1 [50,51]. Primary aliphatic amines can be additionally confirmed by the characteristic bands at 1600-1570 which correspond to bending (deformation) vibration NH 3 ? [25] and C-N stretching vibration located at 1250-1020 cm -1 .…”

“…Apart from well-known non-covalent forces such as dipoledipole or dipole-transient-dipole interactions, new bonding types are identified. These are, for example, d-hole interactions-especially halogen bonding [3,4]. Hydrogen bonding is unquestionably the most important cohesive force in directing the supramolecular organization in the solid state [5].…”

Ab initio and DFT studies of the interaction between carbonyl and thiocarbonyl groups: the role of S···O chalcogen bonds

“…Although the second-order energies are not strictly additive, these data indicate that in all the systems, except for HClCO···CS 2 (a), E 12 > E 21 . Both the AIM and NBO analyses reveal the existence of S5···O interactions and in some cases secondary S5···Cl or Cl···H interactions.…”