Significance of Cations in Ionic Liquids Chemistry

There is a tendancy to classify ionic liquids either as individual solvents (LiCl-KCl vs. NaCl-KCl, NaNO3-KNO3 vs. LiNO3-KNO3) or in terms of the anions. In fact, a compromise is appropriate. We shall point out how the cation choice influences the chemistry, including the electrochemistry, of an anion in an ionic liquid. Some examples follow. The effect of the cation on the structure of liquid alkali halides is exemplified by the coordination chemistry of dissolved Ni(II) as well as by diffraction studies. Raman spectroscopy demonstrates the cation influence on the fundamental equilibrium 2AlCl4- -> Cl- + Al2Cl7- in alkali chloroaluminates. When the electrochemical reduction of NO3- in alkali nitrates is examined, we observe product dependence that can be traced back to metal + oxygen reactions. Regarding the Lewis acidity of room temperature ionic liquids, it has been shown that the cracking of alkanes and the dissolution of heavy oil are influenced by the cation present with a given haloaluminate.