Insights into Ionic Liquid/Aromatic Systems from NMR Spectroscopy: How Water Affects Solubility and Intermolecular...

Area of Science:

• Physical Chemistry
• Materials Science

Background:

• Ionic liquids (ILs) are tunable solvents with diverse applications.
• Understanding structure-property relationships in ILs is crucial for their effective use.

Purpose of the Study:

• To investigate hydrocarbon solubility and chemical interactions in various ionic liquids.
• To elucidate the influence of anion structure on these properties.

Main Methods:

• Utilized 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy.
• Studied ten imidazolium- and pyridinium-based ionic liquids with four distinct anions: thiocyanate [SCN]-, dicyanamide [DCA]-, tricyanomethanide [TCM]-, and bis(trifuoromethylsulfonyl)imide [NTf2]-.

Main Results:

• Anion structure primarily governs anion-aromatic chemical interaction strength, correlating with NMR chemical shift deviations.
• Hydrocarbon solubility is not directly correlated with chemical shift deviations.
• [TCM]- exhibited the largest chemical shift deviations, while [NTf2]- showed the highest hydrocarbon solubility due to steric effects.
• Increased water content significantly reduces hydrocarbon solubility in ILs, with ion-water solvation saturating around 10 molwater/molIL.

Conclusions:

• Anion structure is a key determinant of chemical interactions and solubility in ionic liquids.
• Steric effects of the anion play a significant role in hydrocarbon solubility.
• Water content must be considered when using ILs as solvents for hydrocarbons.