Conformational effects in molecular tectons containing protonated benzimidazole cations

The conformational preferences of protonated 2-benzimidazole cations have been modelled. Non-alkylated benzimidazoles show no strong conformational preferences. but methylation at the N1 position leads to high rotational barriers. The crystal structures are reported for five salts of protonated cations where two or three benzimidazoles are linked by ethylene or cyclohexyl spacers and for one copper(I) complex of a bis-benzimidazole ligand. The conformations observed in the solid state agree with the models. Stacking between benzimidazoles is observed in all cases but one where a high symmetry structure involving six edge-to-face interactions is preferred. Hydrogen bonding to anions or solvent molecules is observed for all salts of protonated benzimidazoles. The packing coefficients of the structures show small but significant variations.