Conductive Metal-Organic Frameworks

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

NON-TECHNICAL DESCRIPTION: Sponge-like crystals with precisely designed nanometer scale pores are critically important for the efficient separation and storage of gases. Technologically, nanoporous semiconductors also show promise as component materials in battery electrodes, chemical sensors, electrocatalysts, and electrochromic materials. Until recently, however, nanoporous crystals have been almost exclusively typecast as electronic insulators. This limitation originates from the trusswork of very strong chemical bonds needed to maintain a stable pore structure. As such, the synthesis of new, electrically conductive, porous crystals stands as an inherently counterintuitive challenge. Efforts toward producing such materials will push the limits of stability and charge delocalization across a crystalline latticework of transition metal nodes and organic linkers. TECHNICAL DESCRIPTION: Metal-organic frameworks are microporous network solids composed of inorganic nodes linked together by organic bridging ligands. While metal-organic frameworks have been extensively developed for their remarkable gas sorption and separation properties, like most porous inorganic materials, they are essentially ionic and electronic insulators. In spite of these properties, this class of materials offers a unique opportunity to explore long-range ion and electron transport in low-dimensional nanoporous systems. The apparent lack of conductive frameworks that have been investigated thus far is not an inherent structural limitation, but rather a result of a lack of focus on electronically interesting structural motifs. That is, the vast majority of frameworks are composed of redox-inactive, closed shell transition metals and organic ligands. In response, metal-organic frameworks engendered with bulk electronic conductivity through the synthesis of open shell and redox-ambiguous scaffolds will be developed. More broadly, the investigation of electronically conductive metal-organic frameworks will explore the limits of long-range electronic communication in low-density hybrid solids and elucidate the primary factors governing the resulting properties. Owing to their crystallinity and the ease of functionalization, metal-organic frameworks can also serve as excellent model systems to better understand and enhance ion transport in nanochannels and nanoporous solids. Thus, the synthesis and characterization of new ion conducting frameworks with a focus on ions that are notoriously difficult to conduct in the solid-state will be pursued.