Missing metal-linker connectivities in a 3-D robust sulfonate-based metal-organic framework for enhanced proton conductivity.

A rare example of a robust, sulfonate-based metal-organic framework (MOF) with a prototypical primitive-cubic topology has been successfully synthesized. Importantly, one-fourth of the metal-ligand connectivities residing in the MOF are missing, resulting in the appearance of coordinatively accessible Cu2+ sites and pendant sulfonate groups. This unprecedented crystal irregularity phenomenon of MOFs substantially enhances their affinity towards water molecules, thus increasing the proton conductivity by two orders of magnitude.