Direct synthesis of an iron metal-organic framework antiferromagnetic glass.

Abstract

We present a direct route to prepare a family of MOF glasses without a meltable crystalline precursor, in contrast to the conventional melt-quenching approach. This one-step synthesis uses the linker itself as the reaction medium under an inert atmosphere, enabling the incorporation of highly hydrolytically unstable M(II) centers. This route produces high-purity iron (II) MOF glasses avoiding the oxidation and partial degradation commonly associated with the conventional melt-quenching process. The transparent glassy monoliths of formula Fe(im)_2-x(bim)_x, denoted as dg-MUV-29 (dg = direct-glass), can be prepared with different amounts of imidazole and benzimidazole as well as with linkers with diverse functionalities (NH₂, CH₃, Br, and Cl). 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 further classes of MOF glasses but also unveiling properties that can be accessed with these materials.