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

The quantum chemical calculations of the molecular complexes of ammonia and phosphine with NH 3 , H 2 O, 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 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.