Three-Dimensional Metal-Catecholate Frameworks and Their Ultrahigh Proton Conductivity

A series of three-dimensional (3D) extended metal catecholates (M-CATs) was synthesized by combining the appropriate metal salt and the hexatopic catecholate linker, H6THO (THO6- = triphenylene-2,3,6,7,10,11-hexakis(olate)) to give Fe(THO)center dot Fe(SO4)(DMA)(3), Fe-CAT-5, Ti(THO)center dot(DMA)(2), Ti-CAT-5, and V(THO)center dot(DMA)(2), V-CAT-.5 (where DMA = dimethylammonium). Their structures are based on the srs topology and are either a 2-fold interpenetrated (Fe-CAT-5 and Ti-CAT-5) or noninterpenetrated (V-CAT-5) porous anionic framework. These examples are among the first catecholate-based 3D frameworks. The single crystal X-ray diffraction structure of the Fe-CAT-5 shows bound sulfate ligands with DMA guests residing in the pores as counterions, and thus ideally suited for proton conductivity. Accordingly, Fe-CAT-5 exhibits ultrahigh proton conductivity (5.0 X 10(-2) S cm(-1)) at 98% relative humidity (RH) and 25 degrees C. The coexistence of sulfate and DMA ions within the pores play an important role in proton conductivity as also evidenced by the lower conductivity values found for Ti-CAT-5 (8.2 X 10(-4) S cm(-1) at 98% RH and 25 degrees C), whose structure only contained DMA guests.