Secondary bonding interactions in some halopyridinium and dihalopyridinium halides

The packing motifs of 2- and 3-chloropyridinium chloride can be interpreted in terms of classical hydrogen bonds N+-H . . . Cl- and non-classical C-H . . . Cl- interactions, with halogen-halogen contacts playing a subordinate role. In the corresponding bromine derivatives, Br . . . Br interactions are much more important. Of the dihalo derivatives, 3,5-dichloropyridinium chloride crystallises with classical linear hydrogen bonds of the form N+-H . . . Cl-, 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(. . . Br-)(2).