Electrochemistry, transport properties and electronic spectroscopy of lanthanide solutes in bis(trifluoromethylsulfonyl)imide-based ionic liquids

The densities, viscosities, ionic conductivities, and surface tensions of 1-(1-butyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyltrimethylammonium bis(trifluoromethylsulfonyl) imide, 1-(1-butyl)-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-(1-butyl)pyridinium bis(trifluoromethylsulfonyl)imide, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide room temperature ionic liquids were measured as a function of temperature. The surface tension of tri-(1-butyl)methylammonium bis(trifluoromethylsulfonyl)-imide was also reported. All of the liquids studied obey the fractional Walden rule and fall only slightly below the ideal line, indicating that they possess high ionicity. Diffusion coefficients of tris(2,2'-bipyridyl)ruthenium(II) were measured in the six ionic liquids. The hydrodynamic radius of tris(2,2'-bipyridyl)ruthenium(II) was estimated from the Stokes-Einstein equation and was found to be remarkably close to the crystallographic radius of this species when the constant was taken as 6.;The heterogeneous kinetics and mass transport of ferrocene/ferrocenium were investigated in the same ionic liquids. Electrochemical impedance spectroscopy measurements indicate that the Fc/Fc+ reaction was electrochemically reversible at freshly activated platinum and glassy carbon electrodes. Previous reports of quasireversibility may be due to the formation of an electrode surface film or uncompensated solution resistance. Diffusion coefficients of Fc and Fc+ scaled linearly with the inverse absolute viscosity in these ionic liquids in accordance with the Stokes-Einstein equation. The Stokes radii of the diffusing species can be calculated by the judicious choice of the constant.;The electrochemistry and electronic absorption spectroscopy of europium, samarium, and ytterbium were investigated in the 1-(1-butyl)-trimethylammonium bis(trifluoromethylsulfonyl)-imide and 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide and in these solvents containing the neutral tridentate ligand N,N,N',N'-tetra( n-octyl)diglycolamide (TODGA) and chloride. Electronic absorption spectroscopy suggested that the Ln3+ species were weakly solvated by Tf2N- as [Ln(Tf2N)p] (p-3)-, p ≥ 3 in the neat ILs. In agreement with previous results, the quasireversible Ln3+/2+ couples of all three elements were accessible in these ILs, but Sm2+ was only stable on the voltammetric timescale. The addition of TODGA to [Ln(Tf2N)p] (p-3)- solutions produced 3:1 complexes with Eu3+ and Sm3+, but only a only 2:1 complex with the smaller Yb3+ ion. Depending on the temperature, the addition of Cl- to solutions induced the precipitation of LnCl3(s) when the mole ratio mCl-/ mLn3+ ≤ 3. However, when mCl -/mLn3+ > 3 these precipitates redissolved to form the octahedral chloride complexes, [LnCl6]3-.