Perspectives on halogen bonding and other σ-hole interactions: Lex parsimoniae (Occam’s Razor)

Many covalently-bonded atoms of Groups IV–VII have regions of positive electrostatic potential (σ-holes) opposite to the bonds, along their extensions. Through these positive regions, the atoms can interact highly directionally with negative sites. (Halogen bonding, in which the σ-hole is on a Group VII atom, is an example of this, and we suggest that hydrogen bonding is as well.) The formation and observed properties of the resulting noncovalent complexes can be fully explained in terms of electrostatics/polarization plus dispersion as the driving forces; this straightforward interpretation is based largely upon physical observables – electrostatic potentials, geometries, interaction energies and electric fields. More elaborate interpretations, involving less physically-based methods and models, have also been advanced. In this paper, we try to reconcile some of these seemingly different approaches.