syn- and anti-H Bonds in Ammonia and Phosphine Complexes with Proton Donors

Abstract

The quantum chemical calculations of the molecular complexes of ammonia and phosphine with NH₃, H₂O, HCl, and HF proton donors were performed by the MP2 method of the second-order Mӧller–Plesset perturbation theory with Dunning’s correlation-consistent aug-cc-pVTZ basis set augmented by diffuse functions. Complexes of two types were considered: with syn (A) and anti (B) orientation of monomers. An analysis of the nature of intermolecular interaction by various methods, including the decomposition of the binding energy into components, showed that the Y···H–X (Y = N, P; X = N, O, Cl, F) interaction in complexes of both types is a hydrogen bond. According to the calculated data, the binding energy in the B complexes is smaller than in the A complexes in accordance with the smaller calculated second-order perturbation energies \(E_{{n{\text{Y}} \to \sigma {\text{*XH}}}}^{{(2)}}\) and electron density at the critical point of the Y···H contact in the B complexes. Elongation of the X–H covalent bond of the donor and red shift of the XH band in the IR spectrum characteristic of molecular systems with an H bond were found for all the complexes.