Organic flux-mediated ligand exchange enables coordination sphere engineering and topological restructuring in 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 their crystalline analogues. Here, we introduce an organic flux-mediated ligand-exchange strategy that enables precise control over both local coordination and global topology in MOF glasses. Crystalline zeolitic imidazolate frameworks (ZIFs) are co-melted with the chelating ligand 1,10-phenanthroline (phen), yielding modified glasses with substantially reduced glass transition temperatures. In Co2+-based systems, phen coordinated directly to the metal nodes, increasing coordination number and reducing network connectivity through the formation of terminal ligands. This coordination sphere engineering affords a level of structural control not readily achievable in conventional inorganic or organic glasses. Crucially, phen 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. This strategy provides a versatile route to MOF glasses with tailored connectivity and metal-centred properties, expanding the design space of hybrid glass materials.