Ultra-Low Viscosity and High Magnetic Susceptibility Magnetic Ionic Liquids Featuring Functionalized Diglycolic Acid Ester Rare-Earth and Transition Metal Chelates

Abstract

Magnetic ionic liquids (MILs) comprise a subcategory of ionic liquids (ILs) and contain a paramagnetic metal center allowing them to be readily manipulated by an external magnetic field. While MILs are popularly employed as solvents in catalysis, separations, and organic synthesis, most low viscosity combinations possess a hydrophilic character that limits their use in aqueous matrices. To date, no study has reported the synthesis and characterization of hydrophobic MILs with viscosities similar to those of hydrophilic MILs and organic solvents while simultaneously exhibiting enhanced magnetic and thermal properties. In this study, diglycolic acid esters are employed as ligands to chelate with paramagnetic metals to produce cations that are paired with metal chelates composed of hexafluoroacetylacetonate ligands to form MILs incorporating multiple metal centers in the cation and anion. Viscosity values below 31.6 cP were obtained for these solvents, the lowest ever reported for hydrophobic MILs. Solubilities in nonpolar solvents such as benzene were observed to be as high as 50% (w/v) MIL-to-solvent ratio while being insoluble in water at concentrations as low as 0.01% (w/v). Effective paramagnetic moment values for these solvents ranged from 5.33 to 15.56 Bohr magnetons (μB), with mixed metal MILs containing multiple lanthanides in the anion generally offering higher magnetic susceptibilities. MILs composed of ligands containing octyl substituents were found to possess thermal stabilities up to 190 °C. The synthetic strategies explored in this study exploit the highly tunable nature of the employed cation and anion pairs to design versatile ultra-low viscosity magnetoactive solvents that possess tremendous potential and applicability in liquid–liquid separation systems, catalysis, and microfluidics where the mechanical movement of the solvent can be easily facilitated using electromagnets.

Neat and rapid preparation of hydrophobic magnetic ionic liquids composed of transition metal chelates featuring in situ formation capabilities in aqueous matrices

“…] anions are procured as alkali metal salts (i.e., Na + and Li + ) 9,26 while ligands used to form the cations are often synthesized using cheap and readily accessible reagents. 24,27 Although the synthetic methodologies used to prepare MILs and/or their starting materials are extensively reported in the literature, the ability to effectively reproduce these reported reaction schemes requires sufficient proficiency in organic/ organometallic chemistry. Additionally, multistep synthesis and purification protocols employed in MIL preparation are time-consuming and often involve the use of dedicated glassware and lab equipment (i.e., rotary evaporator, reflux assembly, etc.)…”

Versatile DNA extraction from diverse plant taxa using ionic liquids and magnetic ionic liquids: a methodological breakthrough for enhanced sample utility

“…By tuning the cation and anion structures, ILs can be customized to interact with a wide range of important biomolecules [18,19]. MILs are a subclass of ILs that possess a paramagnetic metal center in the cation and/or anion and often feature similar physico-chemical properties to ILs [20,21]. The magnetic susceptibility of MILs allows them to be readily manipulated by a magnet in aqueous solutions.…”