From Paramagnetic to Superparamagnetic Ionic Liquid/Poly(ionic liquid): The Effect of π-π Stacking Interaction

Area of Science:

• Materials Science
• Chemistry
• Magnetism

Background:

• Magnetic ionic liquids (MILs) and poly(magnetic ionic liquids) (PMILs) containing FeCl4- anions typically display weak magnetism like paramagnetism or antiferromagnetism at room temperature.
• Natural inorganic ferromagnets with ordered crystal structures serve as inspiration for developing stronger magnetic materials.

Purpose of the Study:

• To synthesize novel soft superparamagnetic ionic liquid (TMBBDI[FeCl4]) and poly(ionic liquid) (PTMBBDI[FeCl4]) materials.
• To investigate the magnetic properties and the role of π-π stacking interactions in enhancing magnetism.

Main Methods:

• Introduction of π-π stacking biphenyl groups into organic cations of MILs and PMILs.
• Characterization of magnetic properties using temperature-dependent studies (100–300 K) and zero-field cooling/field cooling measurements.
• Analysis of ferromagnetic hysteresis loops at 300 K.

Main Results:

• The synthesized TMBBDI[FeCl4] and PTMBBDI[FeCl4] exhibited superparamagnetism between 100 and 300 K.
• A ferromagnetic hysteresis loop was observed at 300 K for both compounds.
• Ferromagnetic interactions were confirmed via zero-field cooling and field cooling studies, unlike MILs/PMILs without π-π stacking.
• π-π stacking interactions were identified as the cause for enhanced magnetism by shortening Fe-Fe distances and increasing molecular order.

Conclusions:

• The incorporation of π-π stacking biphenyl groups significantly enhances the magnetic properties of ionic liquids and polymers.
• The developed materials demonstrate tunable superparamagnetism and ferromagnetism, offering potential for advanced magnetic applications.
• π-π stacking interactions are crucial for achieving strong ferromagnetic behavior in these novel magnetic materials.