Thermal properties of N-alkyl-N-methylpyrrolidinium and N-butylpyridinium fluorometallates and physicochemical properties of their melts

A series of N-alkyl-N-methylpyrrolidinium (RMPyr+, where R = E: ethyl, B: butyl, and H: hexyl) and N-butylpyridinium (BPy+) salts based on the fluorocomplex anions, BF4−, PF6−, SbF6−, NbF6−, TaF6−, and WF7−, have been synthesized and their thermal behavior has been investigated. The melting points of the RMPyr+ salts are above room temperature with the trend; BMPyrAF6 < HMPyrAF6 < EMPyrAF6 for the hexafluorocomplex salts. Some of the salts containing BMPyr+ and HMPyr+ exhibit phase transitions in the solid states. Similar melting points of BPy+ salts of PF6−, SbF6−, NbF6−, TaF6−, and WF7− are observed at around 350 K. Ionic conductivity and viscosity for BMPyrNbF6 (3.0 mS cm−1 and 164 cP at 328 K) are similar to those for BMPyrTaF6 (3.0 mS cm−1 and 165 cP at 328 K), resulting from the similarity of the anions in size. The activation energies of ionic conductivity for the NbF6− and TaF6− salts are 18 and 20 kJ mol−1, and those for viscosity are 23 and 25 kJ mol−1, respectively calculated by Arrhenius equation in the temperature range between 328 and 348 K. Electrochemical windows of BMPyrNbF6, BMPyrTaF6, and BMPyrWF7 are about 4.0, 5.0 and 3.1 V, respectively.

Graphical abstractA series of N-alkyl-N-methylpyrrolidinium (RMPyr+, where R = E: ethyl, B: butyl, and H: hexyl) and N-butylpyridinium (BPy+) salts based on the fluorocomplex anions, BF4−, PF6−, SbF6−, NbF6−, TaF6−, and WF7−, have been synthesized and their thermal behavior has been investigated.Figure optionsDownload full-size imageDownload as PowerPoint slide