Expanding the Electrochemical Window: New Tunable Aryl Alkyl Ionic Liquids (TAAILs) with Dicyanamide Anions.

Abstract

A set of new tunable aryl alkyl ionic liquids (TAAILs) based on the 1-aryl-3-alkyl imidazolium motif has been synthesized, in which the following variables were systematically changed: alkyl chain length, aryl substitution (group and position), and counter ion. TAAILs with dicyanamide (DCA) and bis(trifluoromethylsulfonyl)imide (N(SO2 CF3 )2 , NTf2 ) anions showed remarkable differences of their physical properties: NTf2 ionic liquids were found to have high decomposition temperatures and viscosities well below those of the DCA TAAILs. In contrast, the dicyanamide anion increased the electrochemical stability leading to TAAILs with an extremely wide electrochemical window of up to 7.17 V. Additionally, both classes of TAAILs extract transition metals from aqueous solutions: TAAILs with the DCA anion extract both platinum and copper while TAAILs with the NTf2 anion are selective towards platinum. This demonstrates that minor changes of the molecular structure lead to TAAILs with drastically changed physicochemical properties.