Alcohol modifiers enable tunable melting and glass formation behavior of hybrid coordination networks

Hybrid coordination network glasses (HCNGs) combine the structural tunability of metal-organic frameworks with the processability of inorganic glasses. However, controlling their structure and properties through chemical design remains challenging. Inspired by modifier strategies in oxide glasses, we demonstrate that linear alcohols, ranging from methanol to n-butanol, can tune the thermal behavior of Co(hmba)₃[CoBr₄]-based HCNGs. By increasing the alcohol modifier concentration and alkyl chain length, we observe a monotonic decrease in the melting temperature (T_m, from 114 to 93 °C) and the glass transition temperature (T_g, from 23 to -70 °C) when comparing the pristine and n-butanol-modified systems. Compared to water as a modifier, the various individual short-chain alcohols allow for more tunable thermal properties, but the glass-forming ability is reduced. The change in T_g with alkyl chain length correlates with the dielectric constants of the alcohols, i.e., modifiers with smaller dielectric constants promote greater network flexibility. Analyses reveal that longer-chain alcohols facilitate weakening of the local Co-O coordination environment, promoting dynamic disruption within the hybrid network, while the alcohols can also act as plasticizers in the glass matrix. As such, the decrease in T_m and T_g is attributed to the alcohol molecules disrupting the Co-O linkages, reducing coordination strength, as well as to cooperative effects, where the alcohols act as hydrogen bond donors. These findings establish a direct relationship between modifier chemistry and network dynamics, providing a strategy for designing melt-processable coordination glasses with tunable thermal and structural properties.