Desolvation of metal complexes to construct metal–organic framework glasses

Structural design is an important challenge in glassy materials, including metal–organic framework (MOF) glasses. The current approaches of thermal and mechanical vitrification are mainly limited to azolate and cyanide-based crystalline MOFs, as other MOF crystals usually decompose before melting or upon milling instead of forming stable glasses. Here we report a method for the preparation of MOF glasses by the ‘desolvation’ of solvated metal–ligand discrete complexes. MOF glasses with 12 different ligands of varying lengths, shapes, side and coordination groups (carboxylate, pyridyl and azolate) are synthesized. Hydrogen-bonded networks of the metal complexes pre-assemble metal–ligand arrays, which in turn guide the formation of glass during desolvation. Molecular-level structural transformation studies reveal the network-forming glass structures. The prepared glasses have structural diversity, with tunable pores (sizes and modifications) and good processability, and wide glass transition temperatures ranging from 120 °C to 280 °C. The synthesized glasses with larger ligands have higher crystallization temperatures, affording grain-boundary-free and transparent monoliths under heating without pressure. In this approach, metal–organic framework (MOF) glasses are synthesized by the desolvation of mononuclear metal complexes. The MOF glasses are composed of transition metals and either carboxylate, pyridyl or azolate ligands. Their porous structures and formation of monoliths are regulated in this process.