Large dielectric modulation triggered by spin crossover in polar Hofmann-type polymers

Area of Science:

• Materials Science
• Solid-State Chemistry
• Magnetoelectric Materials

Background:

• Integrating switchable magnetic and electric properties in single-phase materials is crucial for magnetoelectric applications.
• Hofmann-type coordination polymers offer a versatile platform for designing multifunctional materials.

Purpose of the Study:

• To design and synthesize Fe(II)-based Hofmann-type coordination polymers with coupled spin crossover (SCO) and dielectric properties.
• To investigate the effect of ligand geometry and electronic nature on material symmetry and magnetoelectric behavior.

Main Methods:

• Systematic variation of bridging ligands (Bib and Bpt) in Fe(II)-based Hofmann-type coordination polymers.
• Structural characterization to determine symmetry arrangements (centrosymmetric and polar chiral phases).
• Measurement of dielectric properties and spin crossover transitions.

Main Results:

• Two distinct coordination polymers were synthesized: one with a bent Bib ligand (centrosymmetric, moderate dielectric contrast, ~15 K hysteresis) and one with a linear Bpt ligand (polar chiral, gradual SCO from 75-218 K, large dielectric change).
• Ligand-directed control over symmetry was achieved, influencing SCO and dielectric responses.
• Demonstrated magnetoelectric bistability through ligand-enabled symmetry control.

Conclusions:

• Ligand-enabled symmetry control is an effective strategy for realizing magnetoelectric bistability in single-phase materials.
• The synthesized coordination polymers exhibit tunable dielectric responses coupled with spin crossover, showing promise for multifunctional material design.