| Abstract
| - Ab initio studies of complexes HCCH···H2, FCCH···H2, HCCH···HLi, FCCH···HLi, HCCH···HBeH, FCCH···HBeH, HCCH···HBeF, and FCCH···HBeF with H···H intermolecular binding contacts were carried out upto the MP2/6-311++G(3df,3pd)/MP2/aug-cc-pVQZ level of theory. Binding energies extrapolated to thecomplete basis set (CBS) limit indicate that the results obtained at the MP2/6-311++G(3df,3pd) level oftheory are almost saturated. An analysis of the geometrical and energetic parameters was performed, indicatingthat the more strongly bonded complexes could be classified as X−H+δ···-δH−Y dihydrogen bonds, whereasthe weaker ones may belong to the X−H···σ category. In the first case, the electrostatic and exchangecontributions are the most important energetic terms, whereas in the second case, the correlation term alsomakes a sizable contribution to the overall dimer stability. The atoms in molecules (AIM) theory was alsoapplied to explain the nature of all of the complexes. A complete analysis of the different parameters of thecomplexes shows that the stronger complexes may be classified as H bonded and that the weaker complexesmy be classified as van der Waals complexes. However, there is no evident borderline between them, whichindicates the ambiguous nature of dihydrogen-bonded complexes or the arbitrary character of the definitionsused to categorize the molecular complexes.
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