PnicogenBonds: A Theoretical Study Based on the Laplacianof Electron Density.

Although, most of the authors classifythe pnicogen bonds as σ-holebonding, there are some evidence that show they do not require anypositive electrostatic potential around interacting molecules. Inthis work, the Laplacian of electron density is used to study pnicogenbonds in different dimer and trimer complexes. It is shown that thenoncovalent P···P, P···N, and N···Nbonds can be categorized as lump–hole interactions; a regionof charge depletion and excess kinetics energy (hole) in the valenceshell charge concentration (VSCC) of pnicogen atom combines with aregion of charge concentration and excess potential energy (lump)in the VSCC of another molecule and form a pnicogen bond. In fact,since the full quantum potential (according to the local statementof virial theorem) has been used in the definition of the Laplacian,the lump–hole concept is more useful than the σ-holein which the electrostatic part of potential is only considered. Itis shown that the existence of hole in the VSCC of pnicogen atom isresponsible for formation and (in the absence of other interactions)geometry of pnicogen bonded complexes. Because there is (at least)one hole in their VSCC, the pnicogen atoms in PH3, PH2F, H2CPH, H2CPF, andNH2F can engage in direct pnicogen–pnicogen interactions.However, the VSCC of nitrogen atom in the NH3is devoidof hole and hence cannot act as an electron acceptor in pnicogen-bondedcomplexes. [ABSTRACT FROM AUTHOR]