Modulating of the pnicogen-bonding by a H⋯π interaction: An ab initio study.

An ab initio study of the cooperativity in XH2P⋯NCH⋯Z and XH2P⋯CNH⋯Z complexes (X=F, Cl, Br, CN, NC; Z=C2H2,C6H6) connected by pnicogen-bonding and H⋯π interactions is carried out by means of MP2 computational method. A detailed analysis of the structures, interaction energies and bonding properties is performed on these systems. For each set of the complexes considered, a favorable cooperativity is observed, especially in X=F and CN complexes. However, for a given X or Z, the amount of cooperativity effects in XH2P⋯CNH⋯Z complexes are more important than XH2P⋯NCH⋯Z counterparts. Besides, the influence of a H⋯π interaction on a P⋯N (C) bond is more pronounced than that of a P⋯N (C) bond on a H⋯π bond. The quantum theory of atoms in molecules shows that ternary complexes have increased electron densities at their bond critical points relative to the corresponding binary systems. The results also indicate that the strength of the P⋯N(C) and H⋯π interactions increases in the presence of the solvent.