A Multiferroic Spin-Crossover Molecular Crystal.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Molecular Electronics

Background:

• Spin-crossover (SCO) materials offer tunable properties for advanced applications.
• Dual-function switches combining ferroelectricity and SCO are highly sought after but rarely realized in multiferroic crystals.
• Molecular multiferroics with SCO behavior are underexplored.

Purpose of the Study:

• To synthesize and characterize a novel molecular multiferroic crystal exhibiting ferroelectricity, ferroelasticity, and SCO behavior.
• To investigate the impact of fluorine substitution on the phase transition temperature and multiferroic properties.
• To establish the first molecular SCO crystal with multiferroic characteristics.

Main Methods:

• Synthesis of the Fe(II) crystalline complex [FeII(C8-F-pbh)2] (1-F).
• Characterization of phase transitions using temperature-dependent measurements.
• Verification of ferroelectric and ferroelastic properties through domain reversal and evolution studies.
• Analysis of spin transition mechanisms and d-orbital configurations.

Main Results:

• The first molecular multiferroic SCO crystal, 1-F, was successfully synthesized.
• 1-F exhibits a ferroelectric phase transition of 222F2 type with room-temperature ferroelectricity, occurring at 318 K.
• The material displays a spin transition between high- and low-spin states, coupled with ferroelasticity.
• Fluorine substitution significantly increased the transition temperature compared to the parent compound.

Conclusions:

• 1-F represents the first example of a multiferroic SCO molecular crystal.
• The coexistence of ferroelectricity, ferroelasticity, and SCO behavior in 1-F highlights its potential for multistability applications.
• This discovery paves the way for designing novel molecular materials for smart devices.