Theoretical and experimental investigation of the spectroscopic features of and interionic interactions in 1-hexyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium tetrafluoroborate and 1-hexyl-3-methylimidazolium hexafluorophosphate ionic liquids

Abstract

In this work, the spectroscopic and electronic properties of three imidazolium-based ionic liquids (ILs) with 1-Hexyl-3-methylimidazolium cation and chloride, tetrafluoroborate, and hexafluorophosphate anions have been investigated theoretically and experimentally. The ground state electronic structure features such as molecular electrostatic potential, IR and Raman spectra, have been achieved through density functional theory (DFT) calculations at the B3LYP/6–311++G(d,p) level of theory in Gaussian 16. The resulting electron density has been analyzed to reveal intra- and interionic non-covalent interactions via atoms in molecules (AIM) approach and interpreted in terms of both the anion dependency and interaction type. The electronic transition characteristics have been carried out by time-dependent DFT calculations at the same level. The nuclear magnetic resonance shielding constants and chemical shifts have been computed by applying the DFT/gauge-including atomic orbitals (GIAO) method. The experimental measurements associated with the performed calculations include FT-IR and FT-Raman, UV–Vis, and 1H and 13C NMR spectra. The experimental spectroscopic signatures have been interpreted under the light of theoretical calculations. The effect of anion on the electronic structure and spectroscopic features are interpreted in accordance with the that of the density, viscosity, surface tension, refractive index, and the electrical conductivity results from previous works on the physicochemical properties of [Hmim][Cl], [Hmim][BF4], and [Hmim][PF6] ionic liquids. © 2020 Elsevier B.V.