Emergent Magnetic Ordering in Iron(II)-based Metal-Organic Framework Glasses

Metal-organic framework (MOF) glasses combine the structural tunability of crystalline MOFs with the processability of amorphous materials, offering exciting opportunities for functional hybrid materials. We report a one-pot, solvent-free synthesis of two Fe²⁺-based MOF glasses, gFe-bipy (Fe2(im)3(bim)(bipy)) and gFe-tBubipy (Fe2(im)3(bim)(tBubipy)0.25; im– = imidazolate, bim– = benzimidazolate, bipy = 2,2’-bipyridine, tBubipy = 4,4’-di-tert-butyl-2,2’-bipyridine). These glasses feature a continuous random network structure composed of four-connected tetrahedral and octahedral Fe²⁺ nodes. Despite their amorphous nature, both glasses exhibit a high degree of local structural order, enabling strong magnetic exchange interactions between Fe²⁺ centers. Remarkably, these materials are the first MOF glasses to exhibit long-range magnetic ordering, with gFe-tBubipy undergoing an antiferromagnetic ordering transition at 14 K. The magnetic ordering transition of gFe-tBubipy is attributed to its high spin density and specific local structure, distinguishing this antiferromagnetic MOF glass from other amorphous antiferromagnetic materials. The combination of long-range magnetic ordering with exceptionally low glass transition temperatures (Tg = 85–87 °C) positions these materials as highly promising candidates for applications in spintronics, quantum computing and other technologies that benefit from facile processing and shaping. This discovery underscores the transformative potential of MOF glasses as hybrid materials, bridging modular design, processability, and advanced magnetic functionality.