Sodium-Ion-Modified Zeolitic Imidazolate Framework Glasses

Modifying glass compositions is key to creating silicate-based glasses for technologies like optical fibres, catalytic supports, protective coatings, and separation membranes. Here, we extend this concept to metal-organic framework (MOF) glasses by modifying the MOF glass former ZIF-62 (Zn(im)1.8(bim)0.2, im– = imidazolate, bim– = benzimidazolate) with Na(bim) as a compatible glass modifier. Melt-quenching of physical mixtures with varying Na(bim) content (x Na(bim) · Zn(im)1.8(bim)0.2, 0 < x < 1.5) produces modified MOF glasses with a systematic decrease in the glass transition temperature (Tg), and increased liquid fragility, configurational heat capacity (∆C_V) at Tg, and density as x increases – paralleling the chemistry in silicate glasses due to partial network depolymerisation. Structural and spectroscopic analysis, coupled with density-functional theory calculations, confirm that Na(bim) is incorporated homogeneously into the MOF glass network rather than in the MOF pores and reveal the presence of undercoordinated sodium ion environments. Finally, extraction of the modifier by water treatment increases glass porosity, akin to established borosilicate glass processes. Thereby we introduce a transferable approach for tailoring the structure and properties of MOF glasses, expanding possibilities for these functional glass materials.