International Bunsen Discussion Meeting, “Influence of ionic liquids on chemical and physicochemical reactions" location:Clausthal-Zellerfeld (Germany) date:23-25 November 2008
Whereas weakly coordinating anions like the bis(trifluoromethylsulfonyl)imide ion are advantageous for lowering the melting point and viscosity of ionic liquids, their disadvantage is that many types of metal salts have only a limited solubility in these ionic liquids. This behavior can be explained by the poorly solvating properties of the weakly coordination anions. However, for applications like the electrodeposition of metals in ionic liquids, a good solubility of the precursor metal salts is required. One solution to this problem is to switch to ionic liquids with more strongly coordinating anions like the chloride ion, but chloride ionic liquids often have higher melting points and high viscosities. An alternative approach that allows the keep working with bis(trifluoromethylsulfonyl)imide anions is to design functionalized ionic liquids, i.e. ionic liquids with a coordinating functional group attached to the cation.
We have designed different types of new functionalized ionic liquid to fulfil the task of solubilizing large quantities of metal compounds. For instance, carboxylic acid functionalized ionic liquid are excellent solvents in which many transition metal oxides and lanthanide oxides are well soluble. On the other hand, nitrile-functionalized ionic liquid perform well to solubilize metal salts. In order to get a fundamental understanding of the solubilizing process and the solvation of metal ions in these ionic liquids, we are applying different spectroscopic methods (optical absorption spectroscopy, luminescence spectroscopy, FTIR, FT-Raman, EXAFS and HEXS) as well as X-ray diffraction studies on single crystals crystallized from the ionic liquid solutions.