Structural and electronic insights in 1-ethyl-3- methylimidazolium bis (fluorosulfonyl) imide ion pair conformers: ab intio DFT study

Abstract Among all possible ionic liquids, which are potential candidates for electrolytic solvents in lithium ion batteries, 1-ethyl-3-methylimidazolium bis(fuorosulfonyl)imide [EMI[FSI] is the most noteworthy, mainly due to its lower viscosity. To further advance the development of electrolytes with improved electrochemical performance, it is imperative to understand, at a molecular level, the underlying molecular and electronic interactions which influence the viscosity and transport properties of the ionic liquids. With this in mind, therefore, we present detailed structural and electronic insights of imidazolium bis(fluorosulfonyl)imide ion pairs. The structures of cations, anions, and cation-anion ion pairs of the conformers were optimized systematically at ω97X-D levels with the DGDZVD basis sets considering both the empirical dispersion corrections and the presence of a polar solvent, and their most stable geometries were obtained.The nature of molecular interactions in a series of the ion pair conformers were thoroughly discussed by analyzing the interaction energies, stabilization energies and natural orbital analysis of the ion pair conformers.The [FSI]− anions, unlike the [TFSI]− anions, exist on top position with respect to the imidazolium rings. On the basis of a distance criteria, the [EMI]+ and [FSI]− ions show distances of rather weak hydrogen bonds. The [EMI]+ cation and [FSI]− anions tend to form multiple σ* and π* interactions, but reducing the strength of the individual contributions from a potential (linear) maximum.