Theoretical study of pnicogen bonding interactions between PH2X and five-membered heterocycles

Abstract

Intermolecular interactions between PH2X (X=H, F, Cl, Br) and five-member heterocyclic compounds (pyrrole, furan, thiophene) were calculated by using MP2/aug-cc-pVDZ quantum chemical method, and the interaction energies were corrected with BSSE (basis set superposition error) by complete counterpoise correction method. On the basis of MP2/aug-cc-pVDZ optimized geometries, the second-order perturbation stabilization energies (ΔE2) and AIM properties were calculated using the NBO (natural bond orbital) program in Gaussian 03 and AIM 2000 program, respectively. In order to further understand this type of interaction, graphical analyses for representative systems were performed using the reduced density gradient (RDG) color-filled isosurface map and the electronic density difference map. It has been showed that the P-H⋯π hydrogen bonding interaction is formed between PH3 and three five-member heterocyclic compounds, and the pnicogen bonding interactions between PH2X (X=F, Cl, Br) and five-member heterocyclic compounds. There exist two types of pnicogen bonding interactions (π- and n-types) in these complexes, and the stabilities of the π-type pnicogen bonded complexes are stronger than those of the n-type ones. Moreover, the interaction energies have been found to correlate closely with the angle between P-X vector and the direction vector of P atom to the heterocyclic centroid. For comparison, intermolecular interactions between PCl3 and the three kinds of heterocyclic compounds were also studied. It has been showed that three positive electrostatic potential areas (or "σ-hole") are presented at phosphorus atom end along the Cl-P bond in PCl3 molecule, so the complexes with multi-pnicogen-bonding can be formed between PCl3 and the heterocyclic compounds. Through atom in molecule (AIM) analysis, it has been disclosed that the nature of all the pnicogen bonding interactions belongs to the closed-shell electrostatic interactions, and the stabilities of the complexes are correlated positively with the electron densities in the bond critical points (BCPs). RDG graphical analyses are performed to visualize the positions and strengths of the pnicogen bonding. DDF analyses are also done, and indicating that electron density is reduced at phosphorus atom end and increased around the P-X axis and five-member heteroc yclic molecule because of the pnicogen bonding interaction, thus the underlying rearrangement of the electron densities is intuitively reflected. © 2013 Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences.