Insights into Non‐Ideal Behavior of Double Salt Ionic Liquids with Common Cation: Volumetric Behaviour, Molecular Dynamics Simulations and NMR Experiments 

Abstract

The designer concept of ionic liquid (ILs) allows combination of different types of cation with anion to manipulate desire sets of physico-chemical properties. The additional degree of freedom to improve these properties is addition of second IL, i. e. mixture of two pure ILs, known as "Double Salt Ionic Liquids (DSILs)". Depending on variation in physico chemical properties, DSILs could be ideal or non-ideal solution. The present study was explores non-ideal behaviour of three novel combination of imidazolium based DSILs using physico-chemical properties. The proposed DSILs are homogeneous mixtures of two pure ILs with common cation and two different anions: ethylsulfate and bis(trifluoromethylsulfonyl)imide / trifluoromethanesulfonate / thiocyanate. The densities, 1 and speeds of sound, u for proposed DSILs were determined at different temperatures. The excess molar volumes V m E and excess molar isentropic compressibilities K S,m E were calculated and discussed in view of chemical structures of pure ILs, nature of anions and type of interaction between ions. The V m E were found to be positive for all cases, whereas positive or negative K S,m E were observed for studied DSILs. The behaviour of DSILs was explained by molecular dynamics simulations in terms of interaction energies and hydrogen bonds between components of DSILs as well as 1 H NMR results. The results indicate random distribution of anions around imidazolium cation and structural changes during formulation of DSILs.[a] Dr.

Macroscopic Differentiators for Microscopic Structural Nonideality in Binary Ionic Liquid Mixtures

“…On the other hand, only marginal chemical shifts are recorded when mixtures comprising anions with similar hydrogen-bonding ability are probed, for example, [C 2 mim]­[C 2 SO 4 ] x [CF 3 SO 3 ] 1– x (Δβ ∼ 0.2 and Δ V ∼ 45 cm 3 /mol) and [C 2 mim] [C 2 SO 4 ] x thiocyanate [SCN] 1– x (Δβ ∼ 0.06 and Δ V ∼ 65 cm 3 /mol). ; the trends correspond to the characteristics of the regions in which these ionic liquid mixtures are located.…”

“…Additional Ionic Liquid Systems. As an illustration for the utility of Figure 1 0.13, ΔV ∼ 108.3 cm 3 /mol), produces nonideal behavior displayed in the terms of negative deviation for refractive indices and viscosities, while positive deviations were found for the excess molar volumes, 30 implying that the classification inherent in Figure 1 32 the trends correspond to the characteristics of the regions in which these ionic liquid mixtures are located. The general applicability of Figure 1 for predicting nonideal behavior can be further demonstrated using a contrived example of the ionic liquid mixtures containing a common anion (Δβ ∼ 0) as in 1-ethyl-3-methylimdiazolium [C 2 mim] + and 1-n-octyl-3-methylimidazolium [C 8 mim] + combined with [BF 4 ] − (ΔV ∼ 100 cm 3 /mol) at 298.15 K. The binary mixtures have been recently reported to exhibit nonideal behavior reflected in terms of dielectric constants; for a few mixture compositions, the dielectric constant was almost a factor of 2 higher than those for the pure ionic liquids.…”