Alcohols as modifiers in metal−bis(acetamide) hybrid coordination network glasses

Inorganic glasses are well known for allowing continuous composition adjustment through the addition of so-called modifiers or fluxes (e.g., alkali oxides) to network formers (SiO2, GeO2, B2O3, etc.), which result in the breakage of the continuous network structure of the pure network-forming oxide. In comparison, only few meltable and glass-forming hybrid metal-organic networks exist and only recently has the concept of hybrid modifiers been proposed. As such, there is a significant potential for introducing various types of modifiers in hybrid glasses and understanding their impact on the glass structure and properties. In this study, we investigate the impact of alcohol modifiers in metal-bis(acetamide) network glasses. In detail, we incorporate various alcohols (methanol, ethanol, propanol, etc.) as modifiers into a transition metal-based bis-acetamide hybrid coordination network Co(hmba)3[CoBr4], where hmba =N,N'-1,6-hexamethylenebis(acetamide). We characterize their thermal behavior using differential scanning calorimetry (DSC), finding that the addition of alcohol significantly alters the physical properties, including the melting (Tm) and glass transition temperature (Tg). We further investigate the structure of the glasses to compare the mechanisms by which the different alcohols act as modifiers. Generally, we find a significant variation of properties depending on the length of the carbon change of the modifying alcohol. We believe these findings pave a new path for adjusting the transition temperatures of other hybrid crystals, eventually allowing a broader range of melt-quenched hybrid glass compositions while also providing knowledge about the modifier concept in hybrid glass systems.