The crystal structures of eleven salts of protonated cations of composition benzimidazole-(CH2)nbenzimidazole with n between 2 and 6 are reported. Three interactions dominate the crystal structures (in order of decreasing importance): hydrogen bonding with the benzimidazolonium cations acting as H-bond donors and the anions or solvent molecules as acceptors; stacking of the benzimidazolonium cations; an interaction between anion and the C2 atom of the protonated benzimidazole which is assumed to be electrostatic in origin. Changes in anion do not have a great effect, but as the length of the (CH2)n spacer increases stacking becomes less favoured.