Influence of hydrogen bonds on the P⋯P pnicogen bond

Ab initio MP2/aug′-cc-pVTZ calculations have been carried out to investigate the influence of F–H···F hydrogen bonds on the P···P pnicogen bond in complexes nFH:(PH₂F)₂ for n = 1–3. The formation of F–H···F hydrogen bonds leads to a shortening of the P–P distance, a lengthening of the P–F distance involved in the hydrogen bond, a strengthening of the P···P interaction, and changes in atomic populations, NMR ³¹P chemical shieldings, and ^1pJ(P–P) coupling constants. The magnitude of these changes depends on the number of FH molecules and their positions in the complex and are relatively modest except for complexes 2FH:(PH₂F)₂ and 3FH:(PH₂F)₂ that have all FH molecules hydrogen bonded to the same F-atom. For these two complexes, ^1pJ(P–P) decreases as the P–P distance decreases and approaches the value of ¹J(P–P) for P₂H₄. The dramatic changes in these two complexes reflect the changing nature of the hydrogen bonds and the pnicogen bond. Thus, the complex 3FH:(PH₂F)₂ acquires ion-pair character represented as [3(FH)F^–:(H₂P–PH₂F)⁺], and the P···P pnicogen bond acquires significant covalent character. These changes are observed to a lesser extent in 2FH:(PH₂F)₂.