Determination of LFER Descriptors of 30 Cations of Ionic Liquids—Progress in Understanding Their Molecular Interaction Potentials

Abstract

In order to understand molecular interaction potentials of 30 cations of ionic liquids (ILs), the well-known linear free energy relationship concept (LFER) was applied. The LFER descriptors for the excess molar refractivity and the molar volume were calculated in silico and for hydrogen-bonding acidity and basicity, and the polarizability/dipolarity of IL cations were experimentally determined through high performance liquid chromatography (HPLC) measurements. For the study, three different columns (RP-select B, Cyan, and Diol) and buffered mobile phases, based on two organic solvents acetonitrile (ACN) and methanol (MeOH), were selectively combined to the HPLC separation systems RP-select B-ACN, RP-select B-MeOH, Cyan-MeOH, Diol-ACN, and Diol-MeOH. By measuring the retention factors of 45 neutral calibration compounds and calculating LFER descriptors of three cations in the HPLC systems, the system parameters, including an ionic z coefficient, were determined. Conversely, the LFER descriptors of 30 ionic liquid cations were determined, based on the parameters of five systems and their retention factors in the HPLC systems. The results showed that the type of head group, alkyl chain length and further substituents of the cation have a significant influence on the dipolarity/polarizability and the hydrogen-bonding acidity, and functionalized groups (hydroxyl, ether, and dimethylamino) lead to hydrogen-bonding basicity of the cation. The characterization of cationic LFER descriptors opens up the chance for a more quantitative understanding of molecular interaction potentials and physicochemical properties of ILs.

Structural Organization and Supramolecular Interactions of the Task-Specific Ionic Liquid 1-Methyl-3-carboxymethylimidazolium Chloride: Solid, Solution, and Gas Phase Structures

“…Despite all advances made in the comprehension of the properties and structural organization of ILs, fine details are only now starting to emerge. Vast literature is available on the structural organization, − supramolecular interactions, − and (self-) aggregation behavior − of imidazolium-based ILs, but such details for TSILs have remained much less explored. − …”

Volumetric Properties, Molar Surface Gibbs Energy, and Its Application of Binary Systems Containing Ether-Group Functionalized Ionic Liquid with Monohydric Alcohols

“…The O–H stretching vibration is observed at 3316 and 3318 cm –1 for methanol and ethanol, and it is obvious that there is a significant blue shifting of about 240 cm –1 for [C 1 OC 2 pyrr][NTf 2 ]–methanol binary system at x 1 = 0.3 around 3316, and a shifting of 236 cm –1 for [C 1 OC 2 pyrr][NTf 2 ]–ethanol binary system at x 1 = 0.5 around 3318 cm –1 , which imply that H-bonding interactions mainly occurs between the −O– of cation [C 1 OC 2 pyrr] + or −N– of anion [NTf 2 ] − and the hydroxyl group of alcohols. On comparing the IR spectra with other ionic liquids + alcohol solvent mixtures, we found that a similar blue shift is observed, which means the frequency changes are induced by the formation of hydrogen bonds between the hydroxyl group of the alcohol solvent and constituent ions of the ionic liquid. , …”

Descriptors for ions and ion-pairs for use in linear free energy relationships

“…(12) contains no less than seven descriptors and so seven equations are needed with values of log P in seven different solvents even to evaluate the seven simultaneous equations in order to obtain the seven unknown descriptors. In the case of neutral solutes we were able to calculate E and V, and hence to reduce the number of unknown descriptors to be determined, and we employed the same stratagem for ions [34][35][36] and ionic species [37].…”

“…The first attempt to obtain an LFER that included properties of ions was that of Marcus et al [3] but there was no connection with properties of neutral solutes. Cho et al [34,35] have recently used Eq. (1) with an additional descriptor for anions, but the coefficients in Eq.…”