Alkylcyanoborate Anions: Building Blocks for Fluorine-Free Low-Viscosity, Electrochemically and Thermally Stable Ionic Liquids

A set of mixed-substituted potassium alkylcyano- and alkylcyanofluoroborates has been synthesized using easily accessible starting compounds and characterized by elemental analysis, NMR and vibrational spectroscopy, and mass spectrometry. In addition, single-crystal structures of salts of the cyanoborate anions have been derived from X-ray diffraction experiments. The 1-ethyl-3-methylimidazolium room temperature ionic liquids ([EMIm](+)-RTILs) with the new borate anions have been synthesized and their physicochemical properties, that is, high thermal and electrochemical stability, low viscosity, and high conductivity, have been compared to the properties of related [EMIm](+)-RTILs. The influence of the different alkyl substituents at boron has been assessed. The exemplary study on the properties with the [EMIm](+)-ILs with the mixed water stable alkylcyanoborate anions points towards the potential of these fluorine-free borate anions, in general.