Structural microheterogeneity and hydrogen bonding properties in the mixtures of two ionic liquids with a common imidazolium cation

Abstract

A recent focus in the ionic liquid field is to mix two (or more) ionic liquids to expand the available properties. In this work, the interactions and structural properties of 1-ethyl-3-methylimidazolium bis(trifluoromethyl)sulfonylimide (EMIMTFSI) and 1-ethyl-3-methylimidazolium dicyanamide (EMIMDCA) mixtures were investigated by employing multiple experimental methods and DFT calculations. Microheterogeneity of the liquid mixtures was characterized in detail and four complexes or clusters were identified, i.e. 2EMIMTFSI, 2EMIMDCA, 2EMIMTFSI-[DCA]− and 2EMIMDCA-[TFSI]−. Hydrogen bonding interactions between cations and anions were found to be ubiquitous but all in the category of weak interactions. The main interaction sites for [EMIM]+, [TFSI]−, and [DCA]− were found to be C2−H, O/N atoms, and N (in C≡N). This work adds value to an in-depth understanding of the microstructures and molecular interactions in the specified ionic liquid mixtures and would shed light to the general understanding of the ionic liquid systems as a whole.