Synthetic Strategies for Tailoring the Physicochemical and Magnetic Properties of Hydrophobic Magnetic Ionic Liquids

Magnetic ionic liquids (MILs) are a subclass of ionic liquids (ILs) containing paramagnetic components and are readily manipulated by an external magnetic field. Due to their hydrophilic nature, very few applications of MILs in aqueous systems have been reported. In this study, three general classes of hydrophobic MILs including monocationic, symmetrical/unsymmetrical dicationic, and symmetrical/unsymmetrical tricationic MILs were synthesized and characterized. By tuning the structure of the MIL, various physicochemical properties including water solubility, magnetic susceptibility, and melting point were regulated. MILs synthesized with the benzimidazolium cation were shown to exhibit lower water solubility (0.1% (w/v)) when compared to those containing imidazolium cations (0.25% (w/v)). By incorporating asymmetry into the cationic component of the MIL, the melting point of dicationic MILs was lowered while the effective magnetic moment (μ_eff) and hydrophobicity remained unchanged. Tricationic MILs paired with three [FeCl₃Br^–] anions exhibited an μ_eff as high as 11.76 Bohr magnetons (μ_B), the highest ever reported for MILs. The synthetic strategies employed in this study facilitate the generation of hydrophobic MILs that show great promise for liquid–liquid extraction and catalytic studies where the MIL can be easily removed or in microfluidic applications where the MIL microdroplet can be manipulated by an external field