Crystalline hydrogen-bonded supramolecular frameworks (HSFs) as new class of proton conductive materials

In attempt to explore new-type crystalline proton conductive materials in the field of fuel cells, three hydrogen-bonded supramolecular frameworks (HSFs), [M₂(o-CPhH₂IDC)₂(H₂O)₆]·4H₂O (M = Co (1) and Zn (2)) (o-CPhH₄IDC = 2-(2-carboxylphenyl)-1H-imidazole-4,5-dicarboxylic acid) and [Mn(o-CPhH₂IDC)(2,2‧-bipy)(H₂O)₂] (3) (2,2‧-bipy = 2,2‧-bipyridine) have been carefully designed and elaborated with success. HSFs 1-3 show high water and chemical stability thanks to the adoption of imidazole multi-carboxylate ligand. Meanwhile, the hydrogen bond networks inside the frameworks formed by imidazole unit, carboxylate groups, and crystallized water molecules contribute to the high proton transfer performance. All above HSFs have temperature- and humidity-dependent proton conducting properties. Interestingly, the optimized proton conductivities of 1-3 are 1.78 × 10^-4, 1.68 × 10^-4 and 0.54 × 10^-4 Sṡcm^-1 under 98% relative humidity and 100 °C, respectively. Those results are comparable to that of the previously reported crystalline metal-organic frameworks/coordination polymers, covalent organic frameworks, and hydrogen-bonded organic frameworks. This report demonstrates promising application potentials of such crystalline materials in electrochemistry field.