Flux-mediated ligand exchange restructures metal-organic framework glasses

Melt-quenched glasses derived from metal-organic frameworks (MOFs) combine the processability of glasses with the modularity and microporosity of MOFs, yet remain structurally and functionally less diverse than crystalline analogues. Here we show that the chelating ligand 1,10-phenanthroline acts as an organic flux that lowers the glass transition temperature of selected MOFs and induces ligand exchange during melting, thereby enabling control over local coordination and global topology in MOF glasses. In Co²⁺-based systems, phenanthroline coordinates to the metal nodes, increases the coordination number and reduces network connectivity by forming terminal ligands. This coordination sphere engineering affords a level of structural control not readily achievable in conventional inorganic or organic glasses. Crucially, the lower processing temperature suppresses thermal decomposition, enabling the synthesis of Co²⁺-based MOF glasses free of magnetic impurities. These glasses exhibit antiferromagnetic coupling and represent unique examples of magnetic MOF glasses formed by melt quenching. Finally, we extend the strategy to otherwise non-meltable carboxylate-based MOFs, establishing flux-mediated ligand exchange as a versatile route to hybrid glasses with tailored connectivity and properties.