Perfluoroalkyltricyanoborate and Perfluoroalkylcyanofluoroborate Anions: Building Blocks for Low-Viscosity Ionic Liquids.

The potassium perfluoroalkyltricyanoborates K[C F B(CN) ] [n=1 (1 d), 2 (2 d)] and the potassium mono(perfluoroalkyl)cyanofluoroborates K[C F BF(CN) ] [n=1 (1 c), 2 (2 c)] and [C F BF (CN)] [n=1 (1 b), 2 (2 b), 3 (3 b), 4 (4 b)] are accessible with perfect selectivities on multi-gram scales starting from K[C F BF ] and Me SiCN. The K salts are starting materials for the preparation of salts with organic cations, for example, [EMIm] (EMIm=1-ethyl-3-methylimidazolium). These [EMIm] salts are hydrophobic room-temperature ionic liquids (RTILs) that are thermally, chemically and electrochemically very robust, offering electrochemical windows up to 5.8 V. The RTILs described herein, exhibit very low viscosities with a minimum of 14.0 mPa s at 20 °C for [EMIm]1 c, low melting points down to -57 °C for [EMIm]2 b and extraordinary high conductivities up to 17.6 mS cm at 20 °C for [EMIm]1 c. The combination of these properties makes these ILs promising materials for electrochemical devices as exemplified by the application of selected RTILs as component of electrolytes in dye-sensitised solar cells (DSSCs, Grätzel cells). The efficiency of the DSSCs was found to increase with a decreasing viscosity of the neat ionic liquid. In addition to the spectroscopic characterisation, single crystals of the potassium salts of the anions 1 b-d, 2 d, 3 b and 4 c as well as of [nBu N]2 c have been studied by X-ray diffraction.