Abstract
A theoretical calculation has been performed for the ternary complexes XCl∙∙∙FH∙∙∙F- (X=CCH, CN, OH, NC, and F) and the corresponding binary complexes. The halogen bond in the dyad is very weak with the interaction energy less than 2.5kcal/mol. Interestingly, the halogen bond gets a big enhancement when it combines with a very strong hydrogen bond in FH∙∙∙F-, and the largest interaction energy is up to ∼25.6kcal/mol in FCl∙∙∙FH∙∙∙F-. The enhancement of halogen bond not only results in a larger elongation of X-Cl bond and a bigger redshift of the bond stretch vibration but also makes the blue-shifting halogen bond in NCCl∙∙∙FH be a red-shifting one in NCCl∙∙∙FH∙∙∙F-. The halogen bond belongs to a purely close-shell interaction in the dyad, while it becomes a partially covalent interaction in XCl∙∙∙FH∙∙∙F- (X=OH, NC, and F) with negative energy density. In FH∙∙∙F-, the proton is shared between the two F atoms, however, this proton transfers towards the F- end in XCl∙∙∙FH∙∙∙F-.
Published Version
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