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. 2023 Oct 23;1(11):2831-2846.
doi: 10.1021/acsaenm.3c00240. eCollection 2023 Nov 24.

Synthesis, Characterization, and Magnetic Properties of Lanthanide-Containing Paramagnetic Ionic Liquids: An Evan's NMR Study

James E Knoop  1 , Victor Hammed  1 , Liberty D Yoder  1 , Adesewa O Maselugbo  1 , Bolaji L Sadiku  1 , Jeffrey R Alston  1
Affiliations

Synthesis, Characterization, and Magnetic Properties of Lanthanide-Containing Paramagnetic Ionic Liquids: An Evan's NMR Study

James E Knoop et al. ACS Appl Eng Mater. .

Abstract

The present study focuses on the synthesis and characterization of lanthanide-containing paramagnetic ionic liquids (ILs), [CnC1Im]3[MCl3X3] (n = 4, 6, and 8; M = Gd, Dy, and Ho; X = Br and Cl), derived from 1-alkyl-3-methylimidazolium anions. These paramagnetic ILs exhibit low vapor pressure, high thermal stability, physiochemical stability, and tunability, along with significant magnetic susceptibility, making them of interest in advanced material applications that may take advantage of neat liquids with magnetic susceptibility. Structural and physical properties were determined using FTIR, 1H NMR, DSC, and TGA. The room temperature density and viscosity of the iron paramagnetic ILs were also reported. Accompanying this report of paramagnetic IL products, we reintroduce and highlight Evan's NMR technique, an accessible magnetic susceptibility measurement technique that can utilize any available proton NMR to characterize the magnetic susceptibility of ILs. This work demonstrates the robustness of Evan's technique by demonstrating the ability to account for the IL water content, a common issue for hygroscopic materials, during the measurement of magnetic susceptibility. A detailed comparison of the ILs is presented, with dysprosium- and holmium-containing paramagnetic ILs exhibiting the highest magnetic susceptibility reported for mononuclear ILs reported to date. These materials have been studied with an eye on applications for mass transfer, eventually seeking to optimize magnetic susceptibility and viscosity using magnetic field gradients to move paramagnetic ILs carrying solute or heat. The study of paramagnetic ILs is important not only for understanding the magnetic properties of these materials but also for potential applications in areas such as magnetic resonance imaging, biomedicine, environmental remediation, and mass transfer. These unique materials have the potential to bring about new advances and technologies in the fields of materials science and analytical chemistry.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Density (g/mL) of the PILs as a function of the alkyl chain length for the [CnC1Im][FeCl3X] and [CnC1Im]3[MCl3X3] series PILs.
Figure 2
Figure 2
Viscosity as a function of alkyl chain length for the [CnC1Im][FeCl3X] series PILs.
Figure 3
Figure 3
Thermal curves of all of the ILs. (A) TGA plot of [CnC1Im][X] series ILs; (B) TGA plots of [CnC1Im][FeCl3X] series PILs; (C) TGA plot of [CnC1Im]3[HoCl3X3] series PILs; (D) TGA plot of [CnC1Im]3[DyCl3X3] series PILs; (E) TGA plot of [CnC1Im]3[GdCl3X3] series PILs.
Scheme 1
Scheme 1. Chemical Synthesis Pathway for [CnC1Im][FeCl3X] and [CnC1Im]3[MCl3X3] PILs
Figure 4
Figure 4
DSC thermograms of the [CnC1Im][FeCl4] and [CnC1Im]3[MCl6] series PILs. (A) Iron PILs; (B) Holmium PILs; (C) Gadolinium PILs; (D) Dysprosium PILs. DSC thermograms were measured upon heating.
Figure 5
Figure 5
Evan’s Method 1H NMR spectra of [C4C1Im]3[HoCl6]. Top: original NMR sample spiked with 30 μL of anhydrous methanol; bottom: original NMR sample.
Figure 6
Figure 6
Evan’s Method 1H NMR spectra of [C8C1Im]3[HoCl3Br3]. (A) 1H NMR spectra showing peak assignments and deuterated solvent shifts with dashed lines; (B) COSY NMR spectra with dashed lines to illustrate proton propinquity.
Figure 7
Figure 7
Volume magnetic susceptibility of the [CnC1Im][FeCl3X] and [CnC1Im]3[MCl3X3] series PILs. (A) PILs with MCl4 and MCl6 anions; (B) PILs with MCl3Br and MCl3Br3 anions.
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