High Proton Conductivity of Zinc Oxalate Coordination Polymers Mediated by a Hydrogen Bond with Pyridinium

A novel metal–organic framework, (Hpy)2[Zn2(ox)3]·nH2O (n = 0, 1), having a pyridinium cation, was newly synthesized, and the crystal structures were determined. The hydrated compound shows a high proton conductivity of 2.2 × 10–3 S cm–1 at 298 K and 98% relative humidity. Single crystal XRD analysis revealed a rotational displacement factor for the hydrated pyridinium ring and elongated water site that is thought to cause the high proton conductivity.