Theoretical study of cyanophosphines: Pnicogen vs. dipole-dipole interactions

Cyanophosphine derivative dimers, [HXP(CN)]₂ with X=H, F and Cl, have been characterized by means of CCSD(T)/aug'-cc-pVTZ//MP2/aug'-cc-pVTZ computational level calculations. Different interactions have been found upon complexation, such as hydrogen bonds, pnicogen bonds and dipole···dipole interactions. The intermolecular distances range between 2.84 and 3.53Å and the binding energies between -34.7 and -3.6kJmol^-1. Compounds with dipole···dipole interactions present shorter contact distances and larger (more negative) binding energies than those with pure P···P pnicogen bonds. Electron density shift maps show larger variations in compounds with dipole···dipole interactions than in those with pure pnicogen ones, in line with the energetic results. However, NBO analysis suggests that the complexes with P···P pnicogen bonds, in special those with XP···PX (X=F, Cl) show E(2) orbital interaction energies much larger than the dipole···dipole ones.