Strong dihydrogen bonds – ab initio and atoms in molecules study

Strong and medium dihydrogen bonds of complexes for which binding energies amount to 10–20 kcal/mol were investigated. The calculations have been performed up to MP2/aug-cc-pVDZ//MP2/aug-cc-pVTZ level of theory for model systems of NH4+⋯HBeH, NF3H+⋯HBeH and NH4+⋯HBeF. The results indicate that for the NF3H+⋯HBeH complex there is a very short H⋯H intermolecular contact, much shorter than the sum of corresponding van der Waals radii. The analysis of geometrical and energetic data indicates partly covalent nature of H⋯H interaction. The characteristics of the bond critical points – the electron densities and their Laplacians – also confirm this conclusion. Additionally, the extrapolations of the values of interaction energies to the complete basis sets (CBSs) were performed here.