Applying the Influence of Conformational Freedom on the Network Topologies Showing Impressive Proton Conductivity

The present work reports two Zn­(II) based metal–organic frameworks that show excellent proton conductivity with potential application in proton exchange membrane fuel cell development. Two polymeric networks (PDA-FA and PDA-WC) were synthesized using two flexible ligands, a bispyrazole ligand and 1,4-phenyl diacetic acid. Structural studies show some intriguing crystallographic phenomena including the occurrence of different conformations in the same crystal lattice. Furthermore, the compounds exhibit excellent chemical and thermal stability. Both compounds show some important structural features that make them highly suitable candidates for proton conductivity. Compound PDA-FA shows not-so-common immobilized free COOH groups grafted onto the inner surface of the network. An extensively H-bonded water–methanol cluster, on the other hand, dominated the crystal structure of PDA-WC. The above features indicate that both MOFs are suitable for fuel cell development, while further support comes from the corroborating variable temperature proton conductivity data.