Wide spectrum of H⋯H interactions: van der Waals contacts, dihydrogen bonds and covalency

Dihydrogen bonds (DHBs) as a sub-class of H-bond interactions are analyzed in this paper. The results of studies on numerous DHBs obtained at the MP2/6-311++G(d,p) level of approximation are revealed. Different kinds of DHBs are investigated, from weak H⋯H interactions attributed to van der Waals interactions with binding energies amounting to less than 1 kcal/mol, through DHBs of medium strength, to strong interactions possessing characteristics of covalent bonds. The Bader theory as well as the interaction energy components defined within the variation-perturbation method have been applied here to understand the nature of these interactions. Different relationships between the energetic and QTAIM (Quantum Theory of “Atoms in Molecules”) parameters are also analyzed.