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 center dot center dot center dot 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. (c) 2007 Elsevier B.V. All rights reserved.