Can H...σ, π... H+...α and α...H+...α interactions be classified as H-bonded?

The following complexes are analyzed: FH... H-2, C2H2... H+...H-2 and H-2... H+...H-2 where specific interactions possessing characteristics which can be attributed to hydrogen bonds exist (X-H... sigma, pi... H+...sigma and sigma... H+...sigma). High level calculations have been performed for these systems since MP2 method was applied and the following basis sets were used: 6-311++G(d,p), 6-311++G(2df,2pd), 6-311++G(3df,3pd) and the Dunning style aug-cc-pVXZ basis sets where the cardinal number X = 2,3,4,5. Components of the interaction energy were calculated, and the QTAIM theory of Bader was applied in order to analyze in depth the physical nature of the stabilization of these complexes. The results indicate that these interactions possess some characteristics typical for classical hydrogen bonds. (c) 2006 Elsevier B.V. All rights reserved.