Impressive Proton Conductivities of Two Highly Stable Metal-Organic Frameworks Constructed by Substituted Imidazoledicarboxylates.

There is great interest in the promising applications of proton-conductive metal-organic frameworks (MOFs) in the field of electrochemistry. Thus, seeking more types of MOFs with high proton conductivity is of great importance. Herein, we designed and prepared two substituted imidazoledicarboxylate-based MOFs, {[Cd( p-TIPhH2IDC)2]·H2O} n [1; p-TIPhH3IDC = 2- p-(1 H-1,2,4-triazolyl)phenyl-1 H-4,5-imidazoledicarboxylic acid] and [Sr(DMPhH2IDC)2] n [2; DMPhH3IDC = 2-(3,4-dimethylphenyl)-1 H-imidazole-4,5-dicarboxylic acid], and fully explored their water-assisted proton conduction. The best conductivity for 1 of 1.24 × 10-4 S·cm-1 is higher than that of most previous conductive Cd-MOFs under similar conditions. 2 has the highest conductivity (0.92 × 10-3 S·cm-1) among the reported conductive Sr-MOFs. Via structural analysis, Ea values, water vapor adsorptions, and powder X-ray diffraction and scanning electron microscopy tests, reasonable proton pathways and conduction mechanisms were highlighted. It should be emphasized that the N-heterocyclic units (imidazole and triazole) and carboxyl and hydrogen-bonding networks in the frameworks all play crucial roles in the transmission of proton conductivity. Our research offers more choice for the preparation of desired proton-conductive materials.