Tracking the Micro-Heterogeneity and Hydrogen-bonding Interactions in Hydroxyl-Functionalized Ionic Liquid Solutions: A Combined Experimental and Computational Study

Ionic liquids (ILs) are an important class of media that are usually used in combination with polar solvents to reduce costs and tune their physicochemical properties. In this regard, it is essential to understand the influence of adding solvents on the properties of ILs. In this work, the micro-heterogeneity and H-bonding interactions between a hydroxyl-functionalized IL, [HOEmim][TFSI], and acetonitrile (ACN) were investigated by attenuated total reflection Fourier transform infrared spectroscopy and molecular simulations. All studied IL-ACN mixtures were found to deviate from the ideal mixtures. The degree of deviations reaches the maximum at about x(ACN)=0.7 with the presence of both homogeneous clusters of pure IL/ACN and heterogeneous clusters of IL-ACN. With the addition of ACN to IL, the mixtures undergo the transformation from ACN solvated in [HOEmim][TFSI] to [HOEmim][TFSI] solvated in ACN. It is found that the newly formed H-bonding interactions between the IL and ACN is the main factor that contributes to the red shifts of O-H, C-2-H, C-4,C-5-H, and C-alkyl-H of [HOEmim](+) cation, and the blue shifts of C-D, C equivalent to N of ACN, and C-F, S=O of [TFSI](-) anion. These in-depth studies on the mixtures of hydroxyl-functionalized IL and acetonitrile would help to understand the micro-heterogeneity and H-bonding interactions of miscible solutions and shed light on exploring their applications.

Automated summary

Ionic liquids (ILs) are often used in combination with polar solvents to modify their properties, and this study investigated the micro-heterogeneity and H-bonding interactions between a hydroxyl-functionalized IL and acetonitrile. The mixtures deviated from ideal behavior due to the newly formed H-bonding interactions, highlighting the importance of understanding the properties of IL-solvent mixtures for various applications.