Systematic Synthesis and Properties Evaluation of Dicationic Ionic Liquids, and a Glance Into a Potential New Field

Dicationic ionic liquids (DILs), a subset of the ionic liquid (IL) family, have attracted growing interest in recent years, and the range of applications within which they are investigated is constantly expanding. However, data which allows structure to property correlation of a DIL is still limited, and thus selecting an appropriate salt to address a specific challenge can be problematic. In comparison to traditional ILs, DILs physico-chemical properties can be tuned by changing the length and type of spacer which connects the cationic heads as well as the type of cation. This in turn could give rise to symmetrical or asymmetrical DILs. In this work, a systematic study of a homogeneous class of 12 dibromide DILs and 12 di-carboxylate salts has been performed. The latter class of DILs were also compared to mono cation derivatives. The different traditional exchange methods to prepare carboxylate DILs have been evaluated and an insight into the drawbacks encountered is also presented. Prepared DILs were characterized (NMR, TGA, DSC) allowing the influence of the structure on their thermal stability to be understood. Most DILs were obtained as solid salts after careful drying. For some of these compounds, a new possible application was studied, namely their use as hydrogen bond acceptors (HBA) of deep eutectic mixtures, showing again some significant structural related effects.

Molecular Dynamics Simulations of Amide Functionalized Imidazolium Bis(trifluoromethanesulfonyl)imide Dicationic Ionic Liquids

In the present study, the structure and dynamics of three dicationic ionic liquids (DILs) with a functional amide group in the imidazolium ring with bis(trifluoromethanesulfonyl)imide, [TFSI]^- anion has been studied by molecular dynamics (MD) simulations. Densities, radial distribution functions (RDFs), combined distribution functions (CDFs), spatial distribution functions, mean-square displacements (MSD), and self-diffusivities for the ions have been calculated from the MD simulations. The calculated densities for [C₄(amim)₂][TFSI]₂ at different temperatures agreed well with the experimental values. The calculated RDFs and CDFs show that the anions are well organized around the amide group and imidazolium rings and the favorite sites of interaction of the [TFSI]^- ion are the hydrogen atoms of the amide group and hydrogen atoms of the imidazolium ring of the cation. The calculated MSDs indicated that the diffusion coefficients of the studied DILs are 1 order of magnitude smaller than those of DILs with a comparable molar mass.