Intramolecular pnicogen interactions in PHF-(CH2)(n)-PHF (n=2-6) systems.

A computational study of the intramolecular pnicogen bond in PHF-(CH2)n-PHF (n=2-6) systems was carried out. For each compound, two different conformations, (R,R) and (R,S), were considered on the basis of the chirality of the phosphine groups. The characteristics of the closed conformers, in which the pnicogen interaction occurs, were compared with those of the extended conformer. In several cases, the closed conformations are more stable than the extended conformations. The calculated interaction energies of the pnicogen contact, by means of isodesmic reactions, provide values between -3.4 and -26.0 kJ mol(-1). Atoms in molecules and electron localization function analysis of the electron density showed that the systems in the closed conformations with short P···P distances have a partial covalent character in this interaction. The calculated absolute chemical shieldings of the P atoms showed an exponential relationship with the P···P distance. In addition, a search in the Cambridge crystallographic database was carried out to detect those compounds with a potential intramolecular pnicogen bond in the solid phase.