Microscopic properties of two 1-(2′-hydroxylethyl)-3-methylimidazolium-based ionic liquids and methanol mixtures

Abstract

A comprehensive idea about the microscopic property of ionic liquid (IL) − cosolvent system is the key for designing suitable working mixtures with desired properties. In this work, the structure and interaction properties of two binary mixtures containing 1-(2′-hydroxylethyl)-3-methylimidazolium-based IL and methanol were studied by Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) methods. Special attention has been paid on the methyl group of methanol that does not directly participate the hydrogen-bond. The C–D systematic stretching vibrational (vs (C–D)) region of CD3OD was closely examined. With the help of excess infrared spectroscopy and quantum chemical calculations, rich information can be obtained from the vs(C–D) region and the detailed association transformation of the mixing progress can be revealed. The hydrogen-bonds with closed shell interaction and electrostatic dominant properties are found between the hydroxyl group of methanol and the ILs. Methyl group of methanol does not interact with the cation or anion of the ILs, however, it is not a spectator of the hydrogen-bond. Its charge-withdrawing effect can stabilize the hydrogen-bond and plays non-negligible role in the hydrogen-bond formation.