| Abstract [eng] |
Ionic liquids (IL) are substances composed of organic molecular cations and organic or inorganic anions with high chemical, electrochemical and thermal stability. With the development of "green" chemistry, ionic liquids are becoming very attractive for a variety of applications, but their high viscosity is a barrier to wider use. One of the easiest ways to reduce IL viscosity is to dilute it with water. The prospect of modulating the properties of such a sustainable solvent simply by changing the proportion of water in the solvent has received considerable attention. However, predicting the effect of water and its content in mixtures with IL on the properties of ionic liquids becomes the basis for further applications of such systems. The aim of this work is to understand the main features of the intermolecular structure and the changes in 1H NMR spectra 1–butyl–3–methylimidazole tetrafluoroborate IL and its aqueous mixtures, in regards to the change of mixture composition using MD simulations and QM/MM calculations for 1H NMR spectra parameters. After completing MD simulations analysis and QM/MM calculations following conclusions were formed. The calculated densities of [C4mim][BF4] IL and its mixtures with water, qualitatively agree with the experimental data: the decrease in density (and rate of decrease) with increasing molar fraction of water in the system was estimated with sufficient accuracy. As the proportion of water in the mixture increases, water tends to coordinate more with the IL [BF4]– anion than with the [C4mim]+ cation. Also, the local distribution of anions around the imidazole ring is minimally affected by water. The applied MD–QM/MM model qualitatively describes the change of water proton shielding constants as the composition of the mixture changes. However, experimentally acquired the 1H NMR chemical shifts of water protons are more sensitive to changes in mixture composition. The trends of 1–butyl–3–methylimidazole cation proton 1H NMR spectra are reproduced qualitatively and quantitatively using this work methodology, therefore the modeled structural changes were evaluated properly. Therefore, the structure of 1–butyl–3–methylimidazole tetrafluoroborate ionic liquid is relatively stable and resistant to intermolecular structural changes. |
