Investigations On The Microscopic Structures And Interactions In Ionic Liquids Solutions By Infrared Spectroscopy

Ionic Liquids (ILs) are liquids formed solely of ions, and they are finding increasing use in many areas of technology and science. The most prominent feature of Ionic Liquids is that they can be designed for a particular application or to be present a specific set of intrinsic properties. Therefore, the study of the structure-activity relationship is the foundation of the molecule design and application of ionic liquids. In this thesis, by a combination of spectra properties and quantum calculations, we have systematically investigated the structural properties of Ionic Liquids and their interactions with other solvents or gas molecules, especially the hydrogen bond interaction.Water is an impurity commonly presented in ILs since all known ILs can absorb water from the air, traces of water are thought to be ubiquitous in these materials. Therefore, it is of vital importance to investigate the interactions between ionic liquids and water. First, we have investigated the microscopic structure changes and the interactions of ionic liquids with the dilution of water molecules by two-dimensional correlation analysis spectroscopy. The result indicates that, water molecules are more prone to interact with the anions first, and then interact with the cation. The extended H-bond network between cations and anions of pure ILs is destroyed gradually into huge ionic clusters, and then the ionic clusters are further dissociated into solvent-surrounded ionic pairs. Finally, the ionic pairs become the dominant form of the ILs in bulk water. Meanwhile, small water clusters bounded to both the anion part and cation part of the ionic pairs are connecting with each other, thereby a percolating network of "ice-like" water molecules is found in the mixtures.Aprotic Ionic liquids, such as imidazolium-based Ionic-Liquids, have been extensively studied. However, the protic Ionic Liquids, which can be considered as a unique subclass of ILs, are relatively less studied. We have systematically investigated the infrared spectrum and interactons in some protic ionic liquids, such as n-butylammonium acetate (N4Ac), N-methyl imidazolium acetate ([Mim][Ac]) as well as N-methyl imidazolium acetate ([Mim][HCOO]). We have found out that the fast proton transfer equilibrium may be responsible for the cohesion of cations and anions when protic ionic liquids dissolved in aqueous solutions. The AIM analysis of the hydrogen bond N-H…O in N4Ac indicates that small amount of water molecules stabilized the ionic pairs of ILs. Meantime, by the conductivity measurement of the protic ionic liquids, we have predicted their microscopic structures.Recently, Ionic liquids have been widely used in the solvent extraction and separation process. The exploring of the way ionic liquids interacting with organic molecules will shed light on the mechemincs of chemical reactions with ionic liquids. By a series of carefully designed comparative infrared spectroscopic studies, we have quantitively identified the different role played by the direct hydrogen-bond interaction and the indirect hydrogen-bond respectively in the blue-shift of the C-D stretching vibrations of DMSO-d6 methyl group in DMSO-d6/[Bmim][BF4] complexes. Results based on FTIR studies indicate that the direct interaction of C-D…F between DMSO-d6 and the anion [BF4]ˉplays a minor role in the blue-shift of vCD in the mixtures of DMSO-d6/ILs. Whereas, the indirect influence of the hydrogen bond formed by the nearby functional group S=O with C2-H of the cation significantly contributes to the blue-shift of vcD, as can be inferred from the significant differences of the blue-shift in [Bmim][BF4] and 1-buty1-2,3-dimethylimidazolium tetrafluoroborate ([Bm2im][BF4]). In contrast, in the case of DMSO-d6/F2O mixtures, direct hydration of C-H…O between the methyl groups of DMSO-d6 with the oxygen atom of water is mainly responsible for the blue shift of vcD·Furthermore, theoretical calculations revealed that charge migrations as well as rehybridization have a dominant effect on the blue-shift in both mixtures.All in all, by combinations of spectroscopic studies as well as quantum calculations, the relationship between microscopic structures and interactions of ionic liquids is successfully revealed. The frame of studing on the structure-property in ionic liquid is established in the systems. We expect that these methods will shed light on further investigations and may help with the designing of ILs.