Structural Organization and Transport Properties of Novel Pyrrolidinium-Based Ionic Liquids with Perfluoroalkyl Sulfonylimide Anions

Abstract

Room-temperature ionic liquids (RTILs) based on the N-butyl-N-methyl pyrrolidinium cation (PYR(14)(+)) combined with three different fluorinated anions have been prepared and characterized by NMR, conductivity, and rheological measurements. The anions are (trifluoromethanesulfonyl)(nonafluorobutanesulfonyl)imide (IM(14)(-)), bis(pentafluoroethanesulfonyl)imide (BETI(-)), and bis(trifluoromethanesulfonyl)imide (TFSI(-)). Intermolecular anion-cation nuclear Overhauser enhancements (NOEs) have been experimentally observed in all titled compounds. These findings indicate the formation of long-lived aggregates in the bulk liquids. The NOE patterns show marked selectivity and can be rationalized assuming that the perfluorinated moieties of the anions tend to adopt a preferential orientation with respect to the cations, with possible formation of mesoscopic fluorous domains. Self-diffusion coefficients D for the anion and the cation have been measured by DOSY NMR. Diffusion data show similar but not identical values for cation and anion, consistent with local ordering at the molecular level. The observed trend in diffusion coefficients, D(cation) > D(anion) for all compounds, is compatible with a higher degree of intermolecular organization of the anions. This nanoscale organization is connected to rather strong deviations of the experimental conductivities from those estimated from the ion diffusion coefficients through the Nernst-Einstein relationship. The measured viscosities and ion diffusion coefficients in PYR(14)IM(14) and in PYR(14)TFSI have similar temperature dependencies, leading to very close values of the activation energies for these processes. Ab initio density functional calculations on models of a PYR(14)TFSI ion pair lead to the identification of several local minima, whose structure and energy can be qualitatively related to the experimental NOE signals and activation energies.

Pyrazolium- versus Imidazolium-Based Ionic Liquids: Structure, Dynamics and Physicochemical Properties

“…This relationship points out that the cations' hydrodynamic radius is smaller than that of the anions, as previously reported for other classes of ILs. 29,31 The presence of two methyl groups in the cation (for ILs 3 and 4) leads to a reduction of the diffusion coefficient. Similarly, the presence of the dicyanamide counterion slows down the diffusion of the bm 3 pz cation, in comparison with Tf 2 N.…”

Ionic liquids with anions based on fluorosulfonyl derivatives: from asymmetrical substitutions to a consistent force field model

“…a Centro de Química Estrutural, Departamento de Engenharia Química, imide (C 1 C 4 ) 10 were proposed (Fig. 1b).…”

Physical and Electrochemical Investigations into Blended Electrolytes Containing a Glyme Solvent and Two Bis{(trifluoromethyl)sulfonyl}imide-Based Ionic Liquids

“…The nature of the pyrrolidinium ring constrains the location of these two methylene carbons creating a preferred site for anion interaction, 60 increasing the probability of TEGDME coordination with the -CH 2 -or -CH 3 groups of the butyl and methyl groups, respectively. The acyclic [N 1124 ][TFSI], however, is not constrained by a ring structure and, therefore, TEGDME-cation interaction may more readily occur at any of the four alpha hydrogen sites, allowing more effective solvation of the complete ion pair in this case.…”