Synthesis of benzimidazolium hydriodate. The synthesis follows the same strategy of and acid-base salt as for benzimidazolium hydrochloride. Benzimidazole (8.671 g, 73.4 mmol) was dissolved in 25 mL demineralized water in a beaker, followed by the addition of 57% hydriodic acid (18.222 g, 81.2 mmol) with stirring. The solutions were heated to 110 ℃ in an oil bath until all liquid had evaporated, resulting in the formation of gray-black crystalline powder. The powder was dried in a vacuum environment at 110 ℃ for 24 h before being subjected to X-ray diffraction analysis as presented in Supplementary Fig. .