Molecular bricklaying: the protonated benzimidazole moiety as a synthon for crystal engineering

The crystal structures of three salts of diprotonated 1,2-bis(1H-benzimidazol-2-yl)ethane, 1, with tetrahalogenometallates are reported. The crystal lattices are constructed from two types of interactions, the stacking of the protonated benzimidazole groups and N–H⋯Cl hydrogen bonding between the cations and the complex anions. Depending on the conformation of the cation, two- or three-dimensionally stacked structures are formed. A similar packing motif is found with the related cation formed by 1,3-bis(1H-benzimidazol-2-yl)propane, 2, and this suggests that the protonated benzimidazole group may be a useful synthon for crystal engineering.