Fluorosulfonyl-(trifluoromethanesulfonyl)imide ionic liquids with enhanced asymmetry

Abstract

New ionic liquids with an asymmetric anion, fluorosulfonyl-(trifluoromethanesulfonyl)imide (FTFSI), were prepared and their chemical–physical properties were investigated. The ionic liquids based on N-methyl-N-propylpyrrolidinium, PYR₁₃, N-butyl-N-methylpyrrolidinium, PYR₁₄, and N-methoxyethyl-N-methylpyrrolidinium, PYR_12O1, exhibit high electrochemical stability (>5.5 V on platinum) and thermal stability (>250 °C in N₂ and >200 °C in O₂). Due to the highly asymmetric anion, the prepared ionic liquids do not crystallize down to −150 °C while maintaining ionic conductivity above 10⁻⁴ S cm⁻¹ even at −40 °C. Conductivity and viscosity values at 20 °C are in the range 3.5–5.0 mS cm⁻¹ and 30–60 mPa s respectively. PFG-NMR measurements showed high self-diffusion coefficients of cations and the anion.