Special Mixing Behavior of Chelate-based Ionic Liquid with Methanol

Area of Science:

• Physical Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Ionic liquids (ILs) are salts that are liquid at room temperature, with tunable properties.
• The interaction of ILs with solvents is crucial for their applications.
• Chelating anions in ILs introduce unique structural features that can influence solvent interactions.

Purpose of the Study:

• To investigate the interaction mechanism between methanol and two distinct ionic liquids: [C10 mim][Cu(hfacac)3] and [C10 mim][hfacac].
• To understand the role of the chelating anion, tri(hexafluoroacetylaceto)-copper(II), in modulating these interactions.
• To elucidate the structural changes and preferential solvation pathways upon mixing.

Main Methods:

• Fourier Transform Infrared (FTIR) spectroscopy was employed to probe molecular interactions.
• Two-dimensional correlation analysis of FTIR spectra was used to determine the sequence of interactions.
• Small-angle X-ray scattering (SAXS) provided insights into the structural organization of the mixtures.

Main Results:

• Significant deviations in the mixing behavior of [C10 mim][Cu(hfacac)3] with methanol were observed compared to [C10 mim][hfacac].
• FTIR analysis revealed distinct shifts in characteristic peaks (C2-H and C=O) indicating differential interactions with the anion and cation.
• SAXS results, combined with FTIR, proposed that methanol preferentially solvates the chelating cavity in [C10 mim][Cu(hfacac)3], enhancing packing, while interacting with the anion then cation in [C10 mim][hfacac].

Conclusions:

• The chelating structure of the anion in [C10 mim][Cu(hfacac)3] significantly alters methanol's interaction pathway compared to ILs with non-chelating anions.
• Methanol's solvation in [C10 mim][Cu(hfacac)3] involves preferential entry into the chelating cavity, influencing the overall mixture structure.
• The findings highlight the importance of anion design in controlling the solvation behavior and properties of ionic liquid mixtures.