Crystal Structure, Vibrational Spectroscopy and ab Initio Density Functional Theory Calculations on the Ionic Liquid forming 1,1,3,3-Tetramethylguanidinium bis{(trifluoromethyl)sulfonyl}amide

The salt 1,1,3,3-tetramethylguanidinium bis{(trifluoromethyl)sulfonyl}amide, [((CH3)2N)2C=NH2]+[N(SO2CF3)2]− or [tmgH][NTf2], easily forms an ionic liquid with high SO2 absorbing capacity. The crystal structure of the salt was determined at 120(2) K by X-ray diffraction. The structure was found to be monoclinic, space group P21/n with a = 11.349(2), b = 11.631(2), c = 11.887(2) Å, and β = 90.44(3)°. Raman and IR spectra are presented and interpreted. The results are interpreted using ab initio quantum mechanics calculations that also predicted vibrational spectra. The relationship between the transoid (C 2 symmetry) structure of the [NTf2]− ion and the conformationally sensitive bands is discussed.