Does [Tf₂N]⁻ slither? Equivalence of cation and anion self-diffusion activation volumes in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide

Abstract

It has been suggested by Suarez et al. that the bis(trifluoromethylsulfonyl)amide ion translates via a ‘slithering’ motion facilitated by cis-trans conversions and that this mechanism is hindered by a reduction...

A volumetric and intra-diffusion study of solutions of AlCl3 in two ionic liquids – [C2TMEDA][Tf2N] and [C4mpyr][Tf2N]

“…11). In this case, the single Al-species intradiffusion coefficient we were able to measure is (0.88 AE 0.03) of that for the anion at the same composition and temperature [0.16 mol kg À1 , 338 K; calculated from eqn (16)]. This is again more consistent with caging rather than AlCl 3 -[Tf 2 N] À association.…”

“…Subsequently, Harris examined a number of examples using data that had become available since Laity's work and confirmed Laity's suggestion by treating weakly ionised liquids such as water and molecular acids with his methods. 63 Calculation of resistance coefficients for numerous ionic liquid examples since has shown they are almost always positive, 16,23,24,64,65 with very few exceptions. 66,67 This is consistent with Nernst-Einstein deviation parameters, D, lying in the range 0 o D o 0.5, as they do for simple unassociated hightemperature molten salts.…”

“…The [C 4 mpyr] + ion, on the other hand, is cyclic, with a quaternary nitrogen in the saturated ring and only the anion can form complexes with AlCl 3 in this case. 8,9 As is well known, the [Tf 2 N] À ion can exist in both cis and trans conformations, though a high pressure study shows this does not appear to have any effect on selfdiffusion in 1-alkyl-3-methylimidazolium [Tf 2 N] ionic liquids: 16 this is likely to be generally the case, at least in neat ILs.…”

Flexibility is the key to tuning the transport properties of fluorinated imide-based ionic liquids

“…In the ionic liquid, such bulky imide anions move by 'slithering' through the little free space available; however, this interpretation is currently debated. 36,40 Accordingly, conformational exibility is not relevant for anions which have small side groups and thus little sweep volume, such as the bis(uorosulfonyl)imide [NFs 2 ] À anion. 35,36,39 We have previously demonstrated the importance of conformational exibility by comparing two ionic liquids with similar anions, 1-butyl-3-methylimidazolium acetyl(tri-uoromethylsulfonyl)imide ([C 4 C 1 im][NTfAc]) and 1-butyl-3methylimidazolium (methylsulfonyl)(2,2,2-triuoroacetyl) imide ([C 4 C 1 im][NMsTFA]).…”

“…In the ionic liquid, such bulky imide anions move by ‘slithering’ through the little free space available; however, this interpretation is currently debated. 36,40 Accordingly, conformational flexibility is not relevant for anions which have small side groups and thus little sweep volume, such as the bis(fluorosulfonyl)imide [NFs 2 ] − anion. 35,36,39…”