Fibrous/Sheet Nanostructures of Spin-Crossover Complexes With Glycyrrhetinic Acid Glycosides in Polar Solvents: Supramolecular Control of Mixed HS/LS State.

Hybridization of [Fe(qsal)2]Cl·2H2O (qsal: N-(8-quinolinyl)salicylaldimine) with glycyrrhetinic acid glycosides affords novel magnetic materials that exhibit spin-crossover behavior with stabilization of mixed HS/LS states. The glycosides direct the self-assembly of [Fe(qsal)2]+ complexes into fibrous and sheet-like nanostructures in polar solvents, particularly in water, where solvation plays a critical role. The 1:1 molar hybrids were characterized by scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy, and dynamic light scattering, confirming nanostructure formation and aggregation in methanol and aqueous media. Ultraviolet-visible spectroscopy revealed temperature-dependent spin crossover through changes in ligand-to-metal charge-transfer and d-d transitions. Superconducting quantum interference device magnetometry further confirmed spin-crossover behavior, showing distinct magnetic susceptibility changes during heating and cooling cycles, consistent with stabilization of a mixed HS/LS state (high spin:low spin ≈ 1:1). This behavior is attributed to asymmetric packing of the iron complexes within the nanostructures and partial stabilization of the high-spin state in highly polar environments. These results demonstrate that supramolecular organization in polar solvents can effectively modulate spin states, providing a new strategy for designing solution-processable and potentially biocompatible spin-crossover materials.