Molecular Dynamics Simulation and Pulsed-Field Gradient NMR Studies of Bis(fluorosulfonyl)imide (FSI) and Bis[(trifluoromethyl)sulfonyl]imide (TFSI)-Based Ionic Liquids

• DOI: 10.1021/jp911950q
• Publication Date: 2010-05-03T10:28:11Z
• Authors: Oleg Borodin; W. Gorecki; Grant D. Smith; Michel Armand
• Keywords: Imide; Sulfonyl; Pulsed field gradient

The pulsed-field-gradient spin-echo NMR measurements have been performed on 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([emim][FSI]) and [bis[(trifluoromethyl)sulfonyl]imide] ([emim][TFSI]) over a wide temperature range from 233 to 400 K. Molecular dynamics (MD) simulations [emim][FSI], [emim][TFSI], [N-methyl-N-propylpyrrolidinium][FSI] ([pyr(13)][FSI]), [pyr(13)][TFSI] utilizing many-body polarizable force field. An excellent agreement between the ion self-diffusion coefficients MD pfg-NMR experiments has observed for [emim][FSI] [emim][TFSI] ILs. structure factor of [pyr(13)][FSI], [pyr(14)][TFSI], agreed well with previously reported X-ray diffraction data by Umebayashi group. Ion packing in liquid state is compared corresponding ionic crystal. Faster transport found FSI-based ILs that TFSI-based associated smaller size FSI(-) anion lower cation-anion binding energies. A significant artificial increase barriers (by 3 kcal/mol) conformational transitions did not result slowing down transport, indicating insensitive torsional energetic, while same TFSI(-) resulted cation 40-50%. Details rotational translational motion, coupling relaxation are also discussed.