Effects of C(2) Methylation on Thermal Behavior and Interionic Interactions in Imidazolium-Based Ionic Liquids with Highly Symmetric Anions

Abstract

Featured Application: The study aims at making a step towards the rational design of ionic liquids for specific applications. The key to this rational design is to fully understand the structure-property relationships. In other words, knowing the links between the behavior at the molecular and the macroscopic scale will enable to develop materials/fluids with optimal properties for a given application, e.g., a chemical process or an electrochemical device. Abstract:The chemical and physical properties of imidazolium-based ionic liquids are determined by the interactions between the counter-ions. The C(2) position plays an important role in these interactions, as it represents the predominant site for interionic hydrogen bonding. This study shows that the directional hydrogen bonds between highly symmetrical anions (iodide, tetrafluoroborate, hexafluorophosphate) and the C(2)-H group of the 1-methyl-3-propylimidazolium cation determine the molecular and macroscopic behavior in terms of the thermal properties. Upon replacing the C(2) proton by a methyl group, the anion repositions itself at the C(4)/(5) moiety, where it forms a new hydrogen bond, apparently with only one of the two CH groups. In addition, the larger the anion is in diameter, the more likely it will establish further interactions with other parts of the cation, such as the propyl chain.

Clusters of the Ionic Liquid 1‐Hydroxyethyl‐3‐methylimidazolium Picrate: From Theoretical Prediction in the Gas Phase to Experimental Evidence in the Solid State

“…The detailed assignment of the CH bands is subject to an ongoing debate in the community . In the following, we use an assignment that is in concert with our previous studies ,, . The assignments presented in the following are based on our previous work on imidazolium‐based ionic liquids and the recent studies of two [C 2 OHmim] + ‐based ILs and an ammonium‐based picrate salt .…”

Synthesis, thermal properties, vibrational spectra and computational studies of Trioctylmethylammonium bis(trifluoromethylsulfonyl)imide ionic liquid

“…Mikkola et al have reported that the use of Aliquat 336 in many chemical reactions could be limited due to the strong coordination effect of the chloride anion 27 . Hence, the cation-anion interaction in ionic liquids is a key factor determining the physico-chemical properties of ILs 28,29 . The design of new ILs with anions different from Clcould provide interesting physico-chemical properties and, for these reasons, the knowledge about the synthesis, the thermal and vibrational properties and interaction between coupled cation-anion in these ILs are important subjects. Studies on vibrational properties, intermolecular vibrations, molecular conformations, and hydrogen-bonded interactions are of great interest in ionic liquids [30][31][32][33][34] .…”

Experimental and DFT studies on structure, spectroscopic and thermal properties of N-Methyl-N,N,N-trioctylammonium chloride ionic liquid

“…The interesting physicochemical properties and applications that present the ionic liquids (ILs) have allowed the gradual growth in the investigations of these species from different points of view [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. For instance, the quaternary ammonium salt, known as Aliquat 336, presents characteristics properties and major applications [15][16][17][18][19][20].…”

“…Studies on Aliquat 336 containing chloride anion have suggested that its use is limited by the strong coordination effect of that halogen [17]. Hence, the cation-anion interactions play a very important role in the properties of ILs [4,5,9,12]. Currently, the elucidations of all types of interactions in ILs are carried out combining theoretical calculations with different spectroscopic techniques [9,12,14,15].…”