Direct synthesis of an iron metal-organic framework antiferromagnetic glass

Glasses are ubiquitous in our everyday lives but still pose fundamental questions about the nature of order in solids. Typically formed by the rapid cooling of a liquid, these amorphous solids have broad applications, with vitreous silica (SiO2) the most well-known example.1 Most functional glasses are purely inorganic solids, restricting the range of functional properties feasible.2 Recently, a number of new metal-organic framework (MOF) glasses containing molecular components has been discovered by heating their crystalline counterparts to a melting point followed by a rapid cooling, thereby expanding the potential applications of glass materials.3–5 However, the melt-quenched (MQ) approach is limited to MOFs that melt, which is very restrictive as most MOFs readily decompose at heating to comparatively low temperatures.6 The low decomposition temperatures mean that glassy MOF samples typically include impurity decomposition products detrimental to functionality, as optical, electronic and magnetic contaminants. In this work, we present a direct route to prepare a family of MOF glasses without a meltable crystalline precursor. This route produces high-purity iron (II) MOF glasses, avoiding the oxidation and partial degradation commonly associated with the conventional melt-quenching process. The absence of magnetic impurities allows us to study the magnetic properties of the MOF glass itself and show that MOF glasses are good model systems for topologically disordered amorphous antiferromagnets. We also present the functional advantages of direct-glass synthesis by creating free-standing films of glassy MOFs and integrating them in optoelectronic devices. Direct-glass synthesis is thus a powerful route to exploit the true functional potential of glassy MOFs, not only realizing new MOF glasses but also unveiling properties that can be accessed with these materials.7