Emergent Spin‐Glass Behavior in an Iron(II)‐Based Metal–Organic Framework Glass

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. Here, a one-pot, solvent-free synthesis is reported of an Fe2+-based MOF glass, gFe-tBubipy, with the composition [Fe2(im)3.12(bim)0.88(tBubipy)0.11]·[Fe(Cp)2]0.09 (im− = imidazolate, bim− = benzimidazolate, tBubipy = 4,4′-di-tert-butyl-2,2′-bipyridine, Cp− = cyclopentadienyl anion). This material forms a continuous random network structure of four-connected tetrahedral and octahedral Fe2+ nodes and exhibits an exceptionally low glass transition temperature (Tg = 87 °C). Despite its amorphous nature and complex composition, gFe-tBubipy exhibits a high degree of local structural order that enables strong antiferromagnetic exchange interactions between Fe2+ centers. Remarkably, it exhibits clear signatures of spin-glass behavior, with a well-defined magnetic freezing transition ≈14 K. This combination of a MOF glass exhibiting a distinct glass transition with spin-glass magnetism arising from topological disorder and frustrated, short-range magnetic interactions represent a significant advance. This discovery underscores the transformative potential of MOF glasses as a versatile platform for exploring the interplay between structural disorder and cooperative magnetic phenomena in hybrid materials.