Synthesis, conductivity, and vibrational spectroscopy of tetraphenylphosphonium bis(trifluoromethanesulfonyl)imide

The reaction of lithium bis(trifluoromethanesulfonyl)imide with tetraphenylphosphonium bromide in water leads to the formation of tetraphenylphosphonium bis(trifluoromethanesulfonyl)imide ([PPh4+] [(CF3SO2)(2)N-]). The obtained compound was identified'by means of H-1, C-13,F-19 and P-31 NMR spectroscopy. Although it has a structure similar to ionic liquids, it exhibits a melting point above 100 degrees C. Besides describing the synthesis, a detailed characterization of its conductivity and vibrational spectroscopic properties is presented. For the latter, FT-Raman and FTIR/ATR spectroscopies are used in the wave number range from 150 to 3500 cm(-1) and from 600 to 3500 cm(-1), respectively. Density functional theory calculations reveal a minor influence of the interionic interactions on the vibrational structure. Consequently, the computational vibrational spectra of the isolated ions show a good agreement with the experimental data. A detailed vibrational assignment is presented. Furthermore, the conductivity data indicate a solid-solid phase transition about 130 K below the melting point. (C) 2017 Elsevier B.V. All rights reserved.