σ-Hole Opposite to a Lone Pair: Unconventional Pnicogen Bonding Interactions between ZF3 (Z=N, P, As, and Sb) Compounds and Several Donors.

The ability of several pnicogen sp(3) derivatives ZF3 (Z=N, P, As, Sb) to interact with electron-rich entities by means of the opposite face to the lone pair (lp) is investigated at the RI-MP2/aug-cc-pVQZ level of theory. The strength of the interaction ranges from -1 to -87 kJ mol(-1) , proving its favorable nature, especially when the lp is coordinated to a metal center, whereby the strength of the interaction is significantly enhanced. NBO analysis showed that orbital effects are modest contributors to the global stabilization of the pnicogen σ-hole bonded complexes studied. Finally, a selection of Cambridge Structural Database examples are shown that demonstrate the impact of this counterintuitive binding mode in the solid state.