Abbasi Nabeel Mujtaba, De Silva Shashini, Biswas Anis, Anderson Jared L
Department of Chemistry, Iowa State University, Ames, Iowa 50011, United States.
Ames National Laboratory-USDOE, Ames, Iowa 50011, United States.
ACS Omega. 2023 Jul 18;8(30):27751-27760. doi: 10.1021/acsomega.3c03938. eCollection 2023 Aug 1.
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 (μ), 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.
磁性离子液体（MILs）是离子液体（ILs）的一个子类别，含有顺磁性金属中心，使其能够很容易地被外部磁场操控。虽然MILs在催化、分离和有机合成中普遍用作溶剂，但大多数低粘度组合具有亲水性，这限制了它们在水性基质中的应用。迄今为止，尚无研究报道具有与亲水性MILs和有机溶剂相似粘度的疏水性MILs的合成与表征，同时展现出增强的磁性和热性能。在本研究中，二乙醇酸酯用作配体与顺磁性金属螯合，以生成阳离子，这些阳离子与由六氟乙酰丙酮配体组成的金属螯合物配对，形成在阳离子和阴离子中都含有多个金属中心的MILs。这些溶剂的粘度值低于31.6厘泊，这是疏水性MILs有史以来报道的最低值。观察到在非极性溶剂如苯中的溶解度高达50%（重量/体积）的MIL与溶剂比例，而在低至0.01%（重量/体积）的浓度下不溶于水。这些溶剂的有效顺磁矩值范围为5.33至15.56玻尔磁子（μ），阴离子中含有多种镧系元素的混合金属MILs通常具有更高的磁化率。发现由含有辛基取代基的配体组成的MILs具有高达190℃的热稳定性。本研究中探索的合成策略利用了所采用的阳离子和阴离子对的高度可调性，来设计通用的超低粘度磁活性溶剂，这些溶剂在液-液分离系统、催化和微流体中具有巨大的潜力和适用性，在这些领域中可以很容易地使用电磁铁促进溶剂的机械运动。
