The effects of cation-anion interactions on the physical and solvent properties of ionic liquids

The physical properties, solid state analysis, and solvent properties of ionic liquids (ILs) have been investigated. The results from the physical properties study revealed that changes to the cation and anion affect the properties of the ionic liquid, i.e. melting point, surface tension, and density. Initial melting point data revealed the dependence of the melting point on the alkyl chain length. The melting point is depressed with increasing alkyl chain to a certain point. At the alkyl chain length of decyl, the melting point starts to increase. To better understand this shift in melting point, a series of high melting hexafluorophosphate salts were synthesized. These salts were analyzed by crystal packing and close contacts between the cation and anion. The results show cation-anion interactions and shifts in the packing motifs with increasing chain length. The interactions that are seen in the solid state do not necessarily take place in the liquid state.; In an effort to understand the solvent properties of the ILs, a linear solvation energy relationship (LSER) was used to model the solvent properties of IL/water and IL/organic systems. This model will help in predicting the solubility of solutes in the ILs based on the solutes interaction characteristics like polarity and hydrogen bonding characteristics. The LSER method also provides insight into the cation-anion interactions that are present in the liquid state.; The investigation into the physical and solvent properties of ILs has revealed that the properties of the ILs are governed by the cation-anion interactions. The results from physical properties data provide a connection between the solid state results and the LSER results. The combination of the results from all three studies gives insight into the interactions between the cation and anion in these unique liquids. These initial results offer a fundamental understanding of the internal forces within ILs. As the field of ILs increases in depth, a continual updating of the properties of new ILs is need to improve the understanding of these novel solvents.