New 2-methylimidazole-dicarboxylic acid molecular crystals: crystal structure and proton conductivity

Three new proton conducting molecular crystals, 2-methylimidazole glutarate, 2-methylimidazole suberate and 2-methylimidazole azelate, were obtained and their structure was determined by the x-ray diffraction method. The structure of the crystals was found to be of layer-type. A hydrogen bond network between the heterocycle, glutaric acid and water molecules was apparent in a single layer of 2-methylimidazole glutarate, whereas chains consisting of two heterocyclic molecules linked with hydrogen bonds with dicarboxylic acid were distinguished in a single layer of 2-methylimidazole suberate and azelate crystals. Thermal stability of the crystals was characterized by differential scanning calorimetry and the electrical conductivity was studied by the impedance spectroscopy method. The maximum conductivity of 2-methylimidazole glutarate pellets amounts to 3.3 x 10(-2) S m(-1) at 325 K, in the case of 2-methylimidazole suberate pellets the maximum conductivity is 2.4 x 10(-4) S m(-1) at 348 K and for 2-methylimidazole azelate pellets the maximum conductivity reaches 6.9 x 10(-4) S m(-1) at 353 K.