Superprotonic Conductivity in Metal-Organic Framework via Solvent-Free Coordinative Urea Insertion.

Highly stable superprotonic conductivity (>10-2 S cm-1) has been achieved through the unprecedented solvent-free-coordinative urea insertion in MOF-74 [M2(dobdc), M = Ni2+, Mg2+; dobdc = 2,5-dioxido-1,4-benzenedicarboxylate] without an acidic moiety. The urea is bound to open metal sites and alters the void volume and surface functionality, which triggers a significant change in proton conductivity and diffusion mechanism. Solid-state 2H NMR revealed that the high conductivity was attributed to the strengthening of the hydrogen bonds between guest H2O induced by hydrogen bonds in the interface between H2O and the polarized coordinated urea.