Spectroscopic and Theoretical Study of (CF₃SO₂)₂N^- (TFSI^-) and (CF₃SO₂)₂NH (HTFSI)

Abstract

The vibrational properties of the TFSI - anion solvated in a polymer or in water have been studied by comparing its IR and Raman spectra with those of the HTFSI molecule. Ab initio self-consistent field Hartree−Fock calculations have also been performed on the free ion or molecule to investigate their Mulliken charges, equilibrium geometry, and internal force constants. Both experimental and theoretical approaches confirm a pronounced delocalization of the negative charge on the nitrogen and oxygen atoms and a marked double-bond character of the SNS moiety for the anion. This double-bond character is decreased for the HTFSI molecule, leading to rather distinct frequencies for some specific vibrations such as the stretching motions of the SO 2 and SNS groups. The agreement between experimental and calculated spectra is much better for HTFSI than for TFSI - . Tentative explanations are proposed for this difference.