The structure and hydrogen-bond behaviours of binary systems containing ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate and methanol/ethanol

A combination of FTIR and DFT to study the microstructure properties of ionic liquid-acetonitrile-methanol systems

Understanding the structural properties of ionic liquids (ILs) in azeotrope mixtures is crucial for designing and synthesizing IL entrainers tailored for extractive distillation. While extensive research has been conducted to comprehend the molecular properties of IL systems, much of this work has been limited to IL-cosolvent binary mixtures and fails to fully capture the essence of breaking azeotropy. In this study, we utilized Fourier-transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations to study the microstructure of the IL-azeotropic system. Leveraging the high resolution of excess spectroscopy and employing the methanol hydroxyl group as an effective probe, our research focused on the IL-acetonitrile-methanol mixtures. This approach enabled us to pinpoint species transformations during the mixing process, revealing the nature of phase equilibrium changes within the azeotrope. Consequently, our findings offer valuable insights into the microstructures of multicomponent solutions.

Dissolution mechanism of cellulose in a benzyltriethylammonium/urea deep eutectic solvent (DES): DFT-quantum modeling, molecular dynamics and experimental investigation

In this paper, a benzyltriethylammonium/urea DES was investigated as a new green and eco-friendly medium for the progress of organic chemical reactions, particularly the dissolution and the functionalization of cellulose. In this regard, the viscosity-average molecular weight of cellulose (M̄w) during the dissolution/regeneration process was investigated, showing no significant degradation of the polymer chains. Moreover, X-ray diffraction patterns indicated that the cellulose dissolution process in the BTEAB/urea DES decreased the crystallinity index from 87% to 75%, and there was no effect on type I cellulose polymorphism. However, a drastic impact of the cosolvents (water and DMSO) on the melting point of the DES was observed. Besides, to understand the evolution of cellulose-DES interactions, the formation mechanism of the system was studied in terms of H-bond density and radial distribution function (RDF) using molecular dynamics modeling. Furthermore, density functional theory (DFT) was used to evaluate the topological characteristics of the polymeric system such as potential energy density (PED), laplacian electron density (LED), energy density, and kinetic energy density (KED) at bond critical points (BCPs) between the cellulose and the DES. The quantum theory of atoms in molecules (AIM), Bader's quantum theory (BQT), and reduced density gradient (RDG) scatter plots have been exploited to estimate and locate non-covalent interactions (NCIs). The results revealed that the dissolution process is attributed to the physical interactions, mainly the strong H-bond interactions.

The effect of dilution on induced free charge density gradients in room temperature ionic liquids

We report on changes in the magnitude and length scale of the induced free charge density gradient, ρ_f, in three imidazolium room temperature ionic liquids (RTILs) with dilution by methanol and acetonitrile. Using depth- and time-resolved fluorescence measurements of cresyl violet rotational diffusion, we find that ρ_f persists in RTILs to varying degrees depending on RTIL and diluent identity, and in all cases the functional form of ρ_f is not a smooth monotonic diminution in either magnitude or persistence length with increasing diluent, but a stepwise collapse. This finding is consistent with changes in the bulk RTIL as a function of dilution seen using rotational diffusion measurements that show the rotating entity in bulk RTILs exhibits a larger effective hydrodynamic volume than would be expected based on bulk viscosity data for the diluted RTILs. This excess hydrodynamic volume can be understood in the context of aggregation of RTIL ion pairs in the diluted RTIL system. The size of the aggregates is seen to depend on RTIL identity and diluent, and in all cases aggregate size increases with increasing dilution. This finding is consistent with the ρ_f dependence on dilution data. The collapse of ρ_f is seen to correlate with the onset of RTIL ion pair dimer formation, a condition that may facilitate dissociated RTIL ion mobility in the binary system.

Structures and non-covalent interaction behaviours of binary systems containing the ionic liquid 1-(2'-hydroxylethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and chloroform

Mixtures of ionic liquids (ILs) and molecular solvents can overcome the drawbacks (high viscosity, high polarity, and high cost) of pure ILs and extend their practical use. The structural and interaction properties of ILs form the bases for understanding their properties. In this work, the structural properties of the mixtures of an IL, 1-(2'-hydroxylethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2OHMIM][Tf₂N]), with chloroform, a molecular solvent of weak polarity, in various concentrations were analysed using Fourier transform infrared spectroscopy and density functional theory calculations. Excess spectra were used to analyse the infrared spectra. The IL forms a stable ion cluster-CDCl₃ complex with CDCl₃ in the concentration range investigated. In the ion cluster-CDCl₃ complex, the hydrogen atom of CDCl₃ forms hydrogen-bonds with the fluorine atoms of the anion. In addition, the chlorine atom of CDCl₃ forms a halogen-bond with the oxygen atom of the anion. All the hydrogen and halogen-bonds identified between the [C2OHMIM][Tf₂N] ion cluster and CDCl₃ exhibit low strength, closed shells, and electrostatically dominant interactions.

Excess spectroscopy and its applications in the study of solution chemistry

Characterization of structural heterogeneity of liquid solutions and the pursuit of its nature have been challenging tasks to solution chemists. In the last decade, an emerging method called excess spectroscopy has found applications in this area. The method, combining the merits of molecular spectroscopy and excess thermodynamic functions, shows the ability to enhance the apparent resolution of spectra, provides abundant information concerning solution structures and intermolecular interactions. In this review, the thinking and mathematics of the method, as well as its developments, are presented first. Then, research progress related to the exploration of the method is thoroughly reviewed. The materials are classified into two parts, small-molecular solutions and ionic liquid solutions. Finally, potential challenges and the perspective for further development of the method are discussed.

The effect of introducing an ether group into an imidazolium-based ionic liquid in binary mixtures with DMSO

Combined DFT and FTIR investigations reveal interesting hydrogen bonding interactions between dimethyl sulfoxide and an ether-functionalized imidazolium-based ionic liquid.