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Evaluation of Halogenopyridinium Cations as Halogen Bond Donors

We have performed a database survey, structural, and computational study of the potential and the limitations halogenopyridinium cations as halogen bond donors. The database survey demonstrated that adding a positive charge on a halogenopyridine ring increases the probability that the halogen atom will participate in a halogen bond, although for chloropyridines it remains below 60%. Crystal structures of both protonated and N-methylated mono-halogenated pyridinium cations revealed that the iodo- and bromopyridinium cations always form halogen bonding contacts with the iodide anions shorter than the sum of the vdW radii, while chloropyridinium cations mostly participate in longer contacts, or fail to form halogen bonds. Although a DFT study of the electrostatic potential has shown that both protonation and N- methylation of halogenopyridines leads to a considerable increase in the ESP of the halogen σ- hole, it is generally not the most positive site on the cation, allowing for alternate binding sites.

halogen bonding, halogenide anions, halogenopyridine cations, hydrogen bonding

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