Crystal structures of the two salts 2-methyl-1H-imidazol-3-ium nitrate-2-methyl-1H-imidazole (1/1) and 2-methyl-1H-imidazol-3-ium nitrate

The title salts, C4H7N (+)(2)center dot NO3-center dot C4H6N2, (I), and C4H7N2+center dot NO3-, (II), were obtained from solutions containing 2-methylimidazole and nitric acid in different concentrations. In the crystal structure of salt (I), one of the -NH H atoms of the imidazole ring shows half-occupancy, hence only every second molecule is in its cationic form. The nitrate anion in this structure lies on a twofold rotation axis. The neutral 2-methylimidazole molecule and the 2-methyl-1H-imidazol-3-ium cation interact through N-H center dot center dot center dot N hydrogen bonds to form [(C4H6N2)center dot center dot center dot(C4H7N2)(+)] pairs. These pairs are linked with two nitrate anions on both sides through bifurcated N-H center dot center dot center dot (O, O) hydrogen bonds into chains running parallel to [001]. In the crystal structure of salt (II), the C4H7N2+ cation and the NO3- anion are both located on a mirror plane, leading to a statistical disorder of the methyl H atoms. The cations and anions again interact through bifurcated N-H center dot center dot center dot(O, O) hydrogen bonds, giving rise to the formation of chains consisting of alternating anions and cations parallel to [100].