High-Energy X-ray Diffraction and MD Simulation Study on the Ion-Ion Interactions in 1-Ethyl-3-methylimidazolium Bis(fluorosulfonyl)amide

Ion-ion interactions or liquid structures in low-viscosity ionic liquid, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide, [C2mIm+][FSA−] were investigated by high-energy X-ray diffraction (HEXRD) experiments and molecular dynamics (MD) simulations. Experimental X-ray structure factor, Sexp(q) obtained from the HEXRD was successfully deconvoluted into the intra- and the intermolecular components, Sintraexp(q) and Sinterexp(q), respectively, by taking into account the population of cis and trans conformers of the FSA anion to give the corresponding radial distribution functions, Gintraexp(r) and Ginterexp(r), respectively. The Ginterexp(r) exhibits the peaks at 3.5, 4.6 and 5.4 Å, which is well represented by theoretical radial distribution function, GinterMD(r) obtained from MD simulations. From the space distribution function, SDF calculated by MD simulations, it was found that static structure (distance and orientation) of the nearest neighbor intermolecular interaction between cation and anion in [C2mIm+][FSA−] is similar to its analogous ionic liquid, [C2mIm+][TFSA−] where TFSA is bis(trifluoromethanesulfonyl)amide.