A Three-Dimensional Ionic Conjugated Metal-Organic Framework.

Abstract

Catecholate-based conjugated metal-organic frameworks (MOFs) have garnered considerable research interest owing to their tunable structures, exceptional stability, outstanding conductivity, and intrinsic porosity. While most reported materials are limited to two-dimensional (2D) architectures, the design and synthesis of new functional ligands remain a critical challenge. In contrast, three-dimensional (3D) catecholate-based MOFs, despite their promising prospect, are still underexplored. Although ionic MOFs have gained recent progress, their functionality remains limited by ligand design constraints. In this work, we report the design and synthesis of an unprecedented catechol-based ionic conjugated 3D ligand-the tetrabenzo[6,f,j,n][1,5,9,13]tetraazacyclohexadecinenickel(II) (Ni(TAAB)) based monomer, and successfully constructed a new ionic 3D electrically conductive MOF (MOF1). Notably, the ionic nature of MOF1 enables facile membrane formation. Conductivity measurements reveal MOF1 exhibits promising semiconductor properties, with electronic absorption spanning across the visible and near-infrared spectra and a bandgap of 1.28 eV. Remarkably, trifluoroacetic acid-doped MOF1 demonstrates an excellent proton conductivity of 0.36 S/m at 97% relative humidity, making it a mixed electronic-proton conductor. This work provides valuable insights into developing 3D conjugated MOFs as multifunctional ionic materials.