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, [((CH(3))(2)N)(2)C=NH(2)](+)[N(SO(2)CF(3))(2)](-) or [tmgH][NTf(2)], easily forms an ionic liquid with high SO(2) 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 P2(1)/n with a = 11.349(2), b = 11.631(2), c = 11.887(2) A, and beta = 90.44(3) degrees . 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 [NTf(2)](-) ion and the conformationally sensitive bands is discussed.