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-(1H-1,2,4-triazolyl)­phenyl-1H-4,5-imidazoledicarboxylic acid] and [Sr­(DMPhH2IDC)2]n [2; DMPhH3IDC = 2-(3,4-dimethylphenyl)-1H-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