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, H<sub>6</sub>THO (THO<sup>6–</sup> = triphenylene-2,3,6,7,10,11-hexakis­(olate)) to give Fe­(THO)·Fe­(SO<sub>4</sub>) (DMA)<sub>3</sub>, Fe-CAT-5, Ti­(THO)·(DMA)<sub>2</sub>, Ti-CAT-5, and V­(THO)·(DMA)<sub>2</sub>, V-CAT-5 (where DMA = dimethylammonium). Their structures are based on the <b>srs</b> 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 × 10<sup>–2</sup> S cm<sup>–1</sup>) at 98% relative humidity (RH) and 25 °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 × 10<sup>–4</sup> S cm<sup>–1</sup> at 98% RH and 25 °C), whose structure only contained DMA guests.