Germanium-Organic Frameworks: Metalloid-Metalloid Bonding as A Covalent Switch for Linker Redox and Conductivity

Abstract

The diverse structures of metal-organic frameworks (MOFs) originate from the coordination chemistry of ionic metal-ligand bonds, while covalent organic frameworks (COFs) leverage covalent bonding. Between these extremes, extended structures based on metalloids are comparatively rare. This paucity obscures how the chemistry of the metalloid elements, intermediate between the metals and the main group, manifests in the properties of new porous materials. This study presents the chemistry of new examples of germanium-organic frameworks (GeOFs). Two new GeOFs with metalloid GeO4 nodes and redox-active triphenylene hexahydroxyl (THO) linkers, Ge-THO-1 and Ge-THO-2, have been synthesized and characterized. Ge-THO-1 has Ge2+ nodes which become tetravalent with concomitant formation of Ge–Ge bonds in Ge-THO-2 upon activation or air exposure. This structural transformation leads to a 10,000-fold increase in electrical conductivity. These materials are rare examples of GeOFs as well as a unique case where metal-metal bond formation regulates structure and conductivity in porous materials.