Theoretical Probing of Weak Anion–Cation Interactions in Certain Pyridinium-Based Ionic Liquid Ion Pairs and the Application of Molecular Electrostatic Potential in Their Ionic Crystal Density Determination: A Comparative Study Using Density Functional Approach

Abstract

A comprehensive study on the structure, nature of interaction, and properties of six ionic pairs of 1-butylpyridinium and 1-butyl-4-methylpyridinium cations in combination with tetrafluoroborate (BF), chloride (Cl), and bromide (Br) anions have been carried out using density functional theory (DFT). The anion-cation interaction energy (ΔE), thermochemistry values, theoretical band gap, molecular orbital energy order, DFT-based chemical activity descriptors [chemical potential (μ), chemical hardness (η), and electrophilicity index (ω)], and distribution of density of states (DOS) of these ion pairs were investigated. The ascendancy of the -CH substituent at the fourth position of the 1-butylpyridinium cation ring on the values of ΔE, theoretical band gap and chemical activity descriptors was evaluated. The ΔE values were negative for all six ion pairs and were highest for Cl containing ion pairs. The theoretical band gap value after -CH substitution increased from 3.78 to 3.96 eV (for Cl) and from 2.74 to 2.88 eV (for Br) and decreased from 4.9 to 4.89 eV (for BF). Ion pairs of BF were more susceptible to charge transfer processes as inferred from their significantly high η values and comparatively small difference in ω value after -CH substitution. The change in η and μ values due to the -CH substituent is negligibly small in all cases except for the ion pairs of Cl. Critical-point (CP) analyses were carried out to investigate the AIM topological parameters at the interionic bond critical points (BCPs). The RDG isosurface analysis indicated that the anion-cation interaction was dominated by strong H···X and C···X interactions in ion pairs of Cl and Br whereas a weak van der Waal's effect dominated in ion pairs of BF. The molecular electrostatic potential (MESP)-based parameter ΔΔV measuring the anion-cation interaction strength showed a good linear correlation with ΔE for all 1-butylpyridinium ion pairs (R = 0.9918). The ionic crystal density values calculated by using DFT-based MESP showed only slight variations from experimentally reported values.

Interaction in Li@Fullerenes and Li+@Fullerenes: First Principle Insights to Li-Based Endohedral Fullerenes

“…Furthermore, the intensity of dispersion interaction increased quickly as we examined increasingly large cages, due to the greater negative values for E dis . It is well-known that the dispersion interactions are among the important non-covalent interactions for many host-guest systems [44,45,46,47,48]. However, the values we calculated E dis are within 8 kcal for both Li@C n and Li + @C n in this work.…”

“…In order to directly depict the physical image of the interaction between carbon cages and the hosted Li and Li + , here non-covalent interaction analysis is discussed based on the reduced density gradient (RDG). It is well known that RDG has become an effective tool to reveal the non-covalent interaction of various host-guest systems [44,45,46,47,48]. The visualizations of RDG for Li@C n and Li + @C n with n = 20, 24, 44, 48, 50 and 70 are shown in Figure 4.…”

Infrared and Terahertz Spectroscopic Investigation of Imidazolium, Pyridinium, and Tetraalkylammonium Tetrafluoroborate Ionic Liquids

“… 18 It is also known that the tetrafluoroborate anion is weakly coordinated as a local interaction in the pyridinium-based ionic liquid, and it is pointed out that the van der Waals effect, which is weaker than the hydrogen-bonding type interaction, dominates the interaction between the cation and the anion. 58 Tsuzuki et al performed MP2/6-311G** level ab initio calculation for [BF 4 ] − complexes with 1-ethyl-3-metylimidazolium cation [emim] + , 1-ethyl-2,3-dimethylimidazolium cation [emmim] + , ethylpyridinium cation [epy] + , and N -ethyl- N , N , N -trimethylammonium [(C 2 H 5 )(CH 3 ) 3 N] + . 46 The total interaction energies of the ion pair were −85.2, −81.8, −82.4, and −85.2 kcal/mol, respectively, and were not very different.…”

Theoretical screening of bistriazole-derived energetic salts with high energetic properties and low sensitivity

“…Density is one of the most significant factor for energetic materials as higher density means that more energy will be packed per unit volume in these materials. 33 Specifically, crystal density can directly influence the detonation performance which is shown in the Kamlet–Jacobs equation. By replacing the nitro group or inserting the different bridges, the structure of bistriazole was changed, which will cause different effect in density.…”