Designing Glass and Crystalline Phases of Metal-Bis(acetamide) Networks to Promote High Optical Contrast.

Owing to their high tunability and predictable structures, metal-organic materials offer a powerful platform to study glass formation and crystallization processes and to design glasses with unique properties. Here, we report a novel series of glass-forming metal-ethylenebis(acetamide) networks that undergo reversible glass and crystallization transitions below 200 °C. The glass-transition temperatures, crystallization kinetics, and glass stability of these materials are readily tunable, either by synthetic modification or by liquid-phase blending, to form binary glasses. Pair distribution function (PDF) analysis reveals extended structural correlations in both single and binary metal-bis(acetamide) glasses and highlights the important role of metal-metal correlations during structural evolution across glass-crystal transitions. Notably, the glass and crystalline phases of a Co-ethylenebis(acetamide) binary network feature a large reflectivity contrast ratio of 4.8 that results from changes in the local coordination environment around Co centers. These results provide new insights into glass-crystal transitions in metal-organic materials and have exciting implications for optical switching, rewritable data storage, and functional glass ceramics.