In recent years the σ-hole concept was introduced and developed and it was applied to the halogen bond and to the other non-bonding interactions.i According to this concept the halogen bond is the electrostatic attraction between the positive potential of the halogen and the negative Lewis base center. This is because the half-filled p orbital of halogen participates in the covalent bond and there is an electron deficiency in the outer lobe of this p orbital; it is called the σ-hole. Hence the halogen atom electron deficient side may act as the Lewis acid. Such a situation may occur not only for halogen atoms and the σ-hole bond concept was introduced to discuss more extended class of non-bonding interactions. There are also the other examples of studies on non-bonding interactions; for example, the N…P attractive interaction was analyzed recently.ii

i(a) Clark, T.; Hennemann, M.; Murray, J.S.; Politzer, P. J.Mol.Mod. 2007, 13, 291. (b) Politzer, P.; Lane, P.; Concha, M.C.; Ma, Y.; Murray, J.S. J.Mol.Mod. 2007, 13, 305. (c) Murray, J.S.; Lane, P.; Clark, T.; Politzer, P. J.Mol.Mod. 2007, 13, 1033. (d) Politzer, P.; Murray, J.S.; Concha, M.C. J.Mol.Mod. 2008, 14, 659. (e) Murray, J.; Concha, M.C.; Lane, P.; Hobza, P.; Politzer, P. J.Mol.Mod. 2008, 14, 699. (f) Murray, J.; Lane, P.; Politzer, P. J.Mol.Mod. 2009, 15, 723.

ii (a) Scheiner, S. J.Chem.Phys. 2011, 134, 094315. (b) Scheiner, S. J.Phys.Chem. A2011 DOI: 10.1021/jp203964b