Enhancing Proton Conduction in 2D Co–La Coordination Frameworks by Solid-State Phase Transition

We report that a new 2D 3d–4f phosphonate [CoIIILaIII(notpH)(H2O)6]ClO4·5H2O (CoLa-II) can undergo a phase transition above 45 °C and 93% relative humidity, resulting in [H3O][CoLa(notp)(H2O)4]ClO4·3H2O (CoLa-III). The transition is accompanied by the release of the proton from intralayer to interlayer, and thus the proton conductivity of the material is increased by 1 order of magnitude.