Multichannel Magnetic Switching Observed in a Fe(II) Spin-Crossover Compound Bearing Rotatable Ligands

The magnetic properties of materials can be modulated by external stimuli through either spin-state transition or modification of the coordination environment. However, achieving both mechanisms in a single-phase system via sophisticated molecular design remains a formidable challenge. In this work, we present an Fe(II) spin-crossover (SCO) complex incorporating rotatable isoxazole ligands, which exhibits a three-step reversible magnetic transition from 120 to 300 K. In this compound, the metal centers experience two-step SCO transition at ca. 147 and 221 K. Upon further heating, the isoxazole ligands undergo significant rotation around the Fe-N coordination bonds, accompanied by an order-disorder phase transition of the ClO₄^- counteranions. As the rotation of organic ligand can influence the electron-density delocalization between the aromatic ring and Fe ion, an additional magnetic anomaly arises near 245 K. The use of rotatable ligands to build SCO compounds offers a promising avenue toward superior materials capable of integrating switchable properties that stem from both electronic-state transition and molecular structural changes.