Investigations of the Phase Transition and Proton Dynamics in Rubidium Methane Phosphonate Studied by Solid-State NMR

In search of new solid acid proton conductors, we prepared the solid acid rubidium methane phosphonate (RMP). These crystals have a monoclinic structure (P2/c; a = 9.3452, b = 9.3142, and c = 7.5021 Å; β = 101.12). The salt incorporates a hydrated lamellar structure. The 1H MAS NMR reveals two different types of acidic protons as well as the water protons in the lamella. The 1H VT MAS NMR of RMP·2H2O single crystal shows a structural phase …