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

Abstract

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 (THO⁶ˉ = triphenylene-2,3,6,7,10,11-hexakis(olate)) to give Fe(THO)·Fe(SO₄) (DMA)₃, Fe-CAT-5, Ti(THO)·(DMA)₂, Ti-CAT-5, and V(THO)·(DMA)₂, V-CAT-5 (where DMA = dimethylammonium). Their structures are based on the srs topology and are either a two-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 × 10⁻² S cm⁻¹) 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 × 10⁻⁴ S cm⁻¹ at 98% RH and 25 °C), whose structure only contained DMA guests.