Engineering Proton Conductive Metal-Organic Glasses Through Secondary Network Formers

Crystal-liquid-glass phase transitions in coordination polymers (CPs) and metal-organic frameworks (MOFs) have opened new opportunities for materials processing and for accessing novel or enhanced functionalities inherited from their crystalline precursors. However, strategies to modulate the properties of the resulting glassy states, collectively referred to as metal-organic glasses (MOGs), have primarily relied on crystal engineering. Such approaches face intrinsic limitations, as the rare occurrence of melting behavior in CPs/MOFs and the narrow compositional windows that sustain a stable liquid phase restrict access to new structures and properties. Inspired by the compositional tunability of conventional oxide glass, this work explores a strategy to modulate MOG properties by incorporating inorganic zirconium hydrogen phosphate as a secondary network former. We hypothesize that the mismatch between tetrahedrally coordinated Zn²⁺ in the parent MOG and octahedrally coordinated Zr⁴⁺ in the additive induces distinct structural and functional modifications. By systematically varying the content of the zirconium hydrogen phosphate, we demonstrate a linear increase in the glass transition temperature, viscosity, and anhydrous proton conductivity, reaching 2.6 mS cm^-1 at 150°C. These results highlight the potential of translating design principles from inorganic glass science to fine-tune the properties of MOGs.