Secondary Bonding Interactions in Some Halopyridinium and Dihalopyridinium Halides

The packing motifs of 2and 3-chloropyridinium chloride can be interpreted in terms of classical hydrogen bonds N+-H-C1~ and non-classical C-H--C1“ interactions, with halogen-halogen contacts playing a subordinate role. In the corresponding bromine derivatives, BrBr interactions are much more important. Of the dihalo derivatives, 3,5-dichloropyridinium chloride crystallises with classical linear hydrogen bonds of the form N+-H C1_ , but its chlorine-chlorine interactions are at best weak; the corresponding bromine derivative displays aggregates of bromine atoms and three-centre hydrogen bonds N+-H (-B r“ )2 .