Multistability at Room Temperature in a Bent-Shaped Spin-Crossover Complex Decorated with Long Alkyl Chains

Area of Science:

• Materials Science
• Coordination Chemistry
• Magnetism

Background:

• Spin-crossover (SCO) compounds are molecular materials that can switch between low-spin (LS) and high-spin (HS) states.
• SCO materials are of interest for applications in sensors, memory devices, and displays.
• Achieving wide thermal hysteresis and multiple magnetic states at room temperature remains a significant challenge.

Purpose of the Study:

• To synthesize and characterize a novel iron(II) pyridyl-benzohydrazonate complex with long alkyl chains.
• To investigate the spin-crossover behavior and thermal hysteresis of the synthesized compound.
• To explore the potential for magnetic tristability and complex phase transitions in SCO materials.

Main Methods:

• Synthesis of an iron(II) pyridyl-benzohydrazonate complex featuring long alkyl chains.
• Variable-temperature magnetic susceptibility measurements to probe spin transitions and hysteresis.
• Single-crystal X-ray diffraction to determine crystal structures and symmetry changes during phase transitions.

Main Results:

• The synthesized complex exhibits a rare spin-crossover behavior with a wide thermal hysteresis loop encompassing room temperature.
• Upon heating, a spin transition occurs from a LS ground state to an ordered HS-LS phase, involving a symmetry change from monoclinic P2₁/n to orthorhombic P2₁2₁2.
• During cooling, the compound displays a two-step transition, first to a magnetically distinct HS-LS phase (monoclinic P2₁) and then to the LS phase, revealing two superposed thermal hysteretic loops.
• Interconversion between HS-LS phases is driven by structural changes in the alkyl chains, leading to magnetic tristability.

Conclusions:

• The novel iron(II) complex demonstrates unprecedented magnetic tristability at room temperature.
• The combination of cooperative spin transitions and ligand-driven effects enables complex magnetic behaviors.
• This work opens new avenues for designing advanced molecular materials with tunable magnetic properties.