Structural analysis of ionic liquids with symmetric and asymmetric fluorinated anions

Abstract

Ionic liquids (ILs) with relatively low viscosities and broad windows of electrochemical stability are often constructed by pairing asymmetric cations with bisfluorosulfonylimide (FSI−) or bistriflimide (NTf2 −) anions. In this work, we systematically studied the structures of ILs with these anions and related perfluorobis-sulfonylimide anions with asymmetry and/or longer chains: (fluorosulfonyl)(trifluoromethylsulfonyl)imide (BSI0,1−), bis(pentafluoroethylsulfonyl)imide (BETI−), and (trifluoromethylsulfonyl) (nonafluorobutylsulfonyl)imide (BSI1,4−) using high energy X-ray scattering and molecular dynamics simulation methods. 1-alkyl-3-methylimidazolium cations with shorter (ethyl, Im2,1+) and longer (octyl, Im1,8+) hydrocarbon chains were selected to examine how the sizes of nonpolar hydrocarbon and fluorous chains affect IL structures and properties. In comparison with these, we also computationally explored the structure of ionic liquids with anions having longer fluorinated tails.

A Brief Guide to the Structure of High-Temperature Molten Salts and Key Aspects Making Them Different from Their Low-Temperature Relatives, the Ionic Liquids

“…What we mean by this is that whereas it is easy to get transport properties wrong (sometimes very wrong) for ILs, it is hard for a reasonable force field to not show the three typical characteristics of an IL: which are polar–apolar alternation [the so-called prepeak or first sharp diffraction peak (FSDP)], charge alternation, and adjacency correlations. 116 − 126 Each of these features appears in a specific q -range, as shown in Figure 5 (left). 119 , 127 − 134 Instead, structural properties of molten salts including coordination numbers and intermediate range order appear to be quite sensitive to the model and, as opposed to the case for ILs, it is very easy to get these wrong.…”

Synthesis, conformational studies, vibrational spectra and thermal properties, of new 1,4-(phenylenebis(methylene) bis(methyl-imidazolium) ionic liquids

“…Additionally, theoretical chemical calculations of cation-anion energy were done in order to support experimental results. The advantages of using those DILs are due to their important thermal stability in comparison with their asymmetric counterparts [11][12].…”

Understanding the Photoexcitation of Room Temperature Ionic Liquids

“…In this combined experimental (steady‐state and time‐resolved fluorescence quenching) and theoretical (MD simulations) approach it is shown that spherical diffusion‐reaction models are not perfectly suited for reactions in RTILs, but that contact pairs serve to gate the electron transfer. These findings have been intensified in a subsequent study where it is shown that depending on the imidazolium cation the size of the anion led to percolation aggregation influencing physicochemical properties such as conductivity [64] …”