Heavy pnicogen atoms as electron donors in sigma-hole bonds.

DFT calculations evaluate the strength of σ-hole bonds formed by ZH 3 and ZMe 3 (Z = N, P, As, Sb) acting as electron donor. Bond types considered include H-bond, halogen, chalcogen, pnicogen, and tetrel bond to perfluorinated Lewis acids FH, FBr, F 2 Se F 3 As, F 4 Ge, respectively, as well as their monofluorinated analogues. All of the Z atoms can engage in bonds of at least moderate strength, varying from 3 to more than 40 kcal mol -1 . In most cases, N forms the strongest bonds, but the falloff from P to Sb is quite mild. However, this pattern is not characteristic of all cases, as for example in the halogen bonds, where the heavier Z atoms are comparable to, or even stronger than N. Most of the bonds are strengthened by replacing the three H atoms of ZH 3 by methyl groups, better simulating the situation that would be generally encountered. Structural and NMR shielding data ought to facilitate the identification of these bonds within crystals or in solution.