Electrochemical and Spectroscopic Investigation of Ln³⁺ (Ln = Sm, Eu, and Yb) Solvation in Bis(trifluoromethylsulfonyl)imide-Based Ionic Liquids and Coordination by N,N,N′,N′-Tetraoctyl-3-oxa-pentane Diamide (TODGA) and Chloride

Abstract

The electrochemistry and electronic absorption spectroscopy of samarium, europium, and ytterbium were investigated in the 1-(1-butyl)trimethylammonium bis(trifluoromethylsulfonyl)imide (BuMe3NTf2N) and 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BuMePyroTf2N) ionic liquids and in these solvents containing the neutral tridentate ligand N,N,N',N'-tetraoctyl-3-oxo-pentane diamide (TODGA) and the anionic hard ligand chloride. Lanthanide ions were introduced into the ionic liquids by controlled potential oxidation of the respective metals to yield solutions containing Eu(2+), Sm(3+), and Yb(3+), and it was possible to cycle between Eu(2+) and Eu(3+) as well as Yb(3+) and Yb(2+) using controlled potential electrolysis. Electronic absorption spectroscopy suggested that the Ln(3+) species are weakly solvated by Tf2N(-) anions as [Ln(Tf2N)x]((x-3)-) in the neat ILs. The quasireversible Ln(3+/2+) couples of all three elements were readily accessible in these ILs, but Sm(2+) was only stable on the voltammetric time scale. Addition of TODGA to [Ln(Tf2N)x]((x-3)-) solutions produces 3:1 complexes with Eu(3+) and Sm(3+) but only a 2:1 complex with the smaller Yb(3+) ion. Depending on the temperature, addition of Cl(-) to solutions of [Ln(Tf2N)x]((x-3)-) induces precipitation of LnCl3(s) when the mole ratio mCl(-)/mLn(3+) ≈ 3. However, when mCl(-)/mLn(3+) > 3, these precipitates redissolve to form the octahedral chloride complexes, [LnCl6](3-).

A comparative study of the cathodic behaviour of EuCl3 in two imidazolium chloride ionic liquids, the 1-butyl-3-methylimidazolium (C4mimCl) and the 1-ethyl-3-methylimidazolium (C2mimCl), on a glassy carbon electrode

“…2-3 also depict examples of the CVs registered with a solution of EuCl 6 3 − (i.e. EuCl 3 dissolved in a rich chloride ionic liquid) [23,27] on a glassy carbon electrode. In both imidazolium ILs, the electro-reduction of EuCl 6 3 − takes place through only one electrochemical step giving rise to a group of signals A/A′ with the shape expected for an electrochemical system in which the oxidized and reduced species are soluble in the media, and that can be assigned to the reduction of EuCl 6 3 − and the oxidation of the electro-generated EuCl 6 4 − .…”

“…1. Electrochemical decomposition mechanism of (a) C 2 mim + [27], and (b) C 4 mim + [4]. (1) formation of the imidazolium radical, (2) disproportionation reaction of two radicals, (3) coupling reaction of two radicals, (4) cage-formation reaction of two imidazolium radicals.…”

“…The electroreduction of Eu(III) and Sm(III) has also been studied in molten chloroaluminates [22][23][24], molten chlorides (e.g. LiCl-KCl and CaCl 2 -NaCl) [25][26] and bis(trifluoromethylsulfonyl)imide (NTf 2 ) based ionic liquids [27] in all cases, the electroreduction of the respective Ln(III) to Ln(II) takes place following the sequence of the cathodic potential: Sm(III) > Eu(III). More recently the electroreduction of Eu(III) has been studied by Rama et al [28] in the 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C 6 mim)NTf 2 containing tri-nbutyl phosphate and N,N-dihexyloctanamide ligands, the electrochemical system Eu(III)/Eu(II), free of any adsorption process, has been found quasi-reversible being the activation energy for Eu (III) diffusion 88 kJ mol − 1 .…”

Electrochemical Behavior of U(VI) in Imidazolium Ionic Liquid Medium Containing Tri‐n‐butyl Phosphate and Chloride Ion and Spectroscopic Characterization of Uranyl Species

“…The feasibility of the electrodeposition of cesium and strontium from ionic liquid medium containing calixerenes and crown ether ligands ionophores was investigated by Hussey and co‐workers and reported the possibility of electrodeposition . In addition, they also investigated the electrochemical behaviour of some trivalent lanthanide ions in ionic liquid medium containing the neutral tridentate ligand, N,N,N′,N′‐tetra(n‐octyl)diglycolamide (TODGA) . The authors reported the electrochemistry and electronic absorption spectroscopy of these lanthanide ions in neat ionic liquid as well as in the ionic liquid phase containing TODGA and chloride ion.…”

“…In addition, the required ligand can be selected in such a way that it undergoes easy oxidation at the counter electrode during the reduction of metal species at the working electrode. One such monoatomic ligand could be a halide anion ,,…”