On the Ability of Nitrogen to Serve as an Electron Acceptor in a Pnicogen Bond
Steve Scheiner
Abstract
Whereas pnicogen atoms like P and As have been shown repeatedly to act as electron acceptors in pnicogen bonds, the same is not true of the more electronegative first-row N atom. Quantum calculations assess whether N can serve in this capacity in such bonds and under what conditions. There is a positive π-hole belt that surrounds the central N atom in the linear arrangement of NNNF, NNN-CN, and NNO, which can engage a NH3 base to form a pnicogen bond with binding energy between 3 and 5 kcal/mol. Within the context of a planar arrangement, the π-hole above the N in NO2OF, N(CN)3, and CF3NO2 is also capable of forming a pnicogen bond, the strongest of which amounts to 11 kcal/mol with NMe3 as base. In their pyramidal geometry, NF3 and N(NO2)3 engage with a base through the σ-hole on the central N, with variable binding energies between 2 and 9 kcal/mol. AIM and NBO provide somewhat different interpretations of the secondary interactions that occur in some of these complexes.