Competition between Lone Pair-π, Halogen Bond, and Hydrogen Bond in Adducts of Water with Perhalogenated Alkenes C2ClnF4-n (n = 0-4)

A thorough search of the potential energy surface is carried out for heterodimers of water with C2ClnF4n. Three different types of interactions are observed. Structures dominated by a lone pair-π interaction have the highest binding energies, and are stabilized by charge transfer from O lone pairs of H2O to the C-C π* antibonding orbital of the alkene. Halogen-bonded O··Cl complexes are slightly less strongly bound, followed by OH··X hydrogen bonds. The replacements of Cl by F atoms have only small effects upon binding energies. Inclusion of vibrational and entropic effects removes the clear energetic superiority of lp-π binding energies. When combined with the observation of several similar geometries for each particular heterodimer type, and a sensitivity to basis set, it would be quite difficult to predict with any degree of certainty the single most stable configuration, even with very high level calculations. *[email protected]