Hydrogen bonding and halogen–halogen interactions in 4-halopyridinium halides

The solid state structures of the 4-halopyridinium halides 4-XC5H4NH+X- (X=Cl, Br, I) all display chains of the form [···X–C5H4N–H+···X-···X–C5H4N–H+···X-···] involving N–H···X- hydrogen bonds and X···X- contacts; the former become longer and the latter shorter (relative to the sum of the van der Waals radii) with increasing size of X.