Cooperative Crystallization of Heterometallic Indium-Chromium Metal-Organic Polyhedra and Their Fast Proton Conductivity

Abstract

Metal-organic polyhedra (MOPs) or frameworks (MOFs) based on Cr 3+ are notoriously difficult to synthesize, especially as crystals large enough to be suitable for characterization of the structure or properties. It is now shown that the co-existence of In 3+ and Cr 3+ induces a rapid crystal growth of large single crystals of heterometallic In-Cr-MOPs with the [M 8 L 12 ] (M=In/Cr, L=dinegative 4,5-imidazole-dicarboxylate) cubane-like structure. With a high concentration of protons from 12 carboxyl groups decorating every edge of the cube and an extensive H-bonded network between cubes and surrounding H 2 O molecules, the newly synthesized In-Cr-MOPs exhibit an exceptionally high proton conductivity (up to 5.8×10 -2 S cm -1 at 22.5°C and 98% relative humidity, single crystal).