Ionic liquids based on the bis(trifluoromethylsulfonyl)imide anion for high-pressure Raman spectroscopy measurements


Correspondence to: Mauro C. C. Ribeiro, Laboratório de Espectroscopia Molecular, Instituto de Química, Universidade de São Paulo, C.P. 26077- CEP 05513-970 - São Paulo, SP – Brazil.



Assembling a diamond anvil cell for high-pressure measurements involves placing in a gasket hole the sample of interest, a pressure transmitting fluid, and a material for pressure calibration. In this communication, we propose the use of ionic liquids containing the bis(trifluoromethylsulfonyl)imide anion ([Tf2N]-), [(CF3SO2)2 N]-, as a simultaneous pressure transmitting and calibrant material for high-pressure Raman spectroscopy measurements of solid samples that are not soluble in ionic liquids. The position of the characteristic Raman band of the [Tf2N]- anion at 740 cm−1 exhibits linear frequency shift for pressures up to 2.5 GPa. High-pressure Raman spectra of different ionic liquids containing the same anion indicate that the actual magnitude of the pressure-induced frequency shift of the [Tf2N]- normal mode depends on the counterion, the typical shift being 4.2 cm−1/GPa. Ionic liquids based on the [Tf2N]- anion are also good pressure transmitting mediums because hydrostatic condition is kept at high pressure, and no crystallization is observed up to 4.0 GPa. Copyright © 2012 John Wiley & Sons, Ltd.