title: Electrochemical and spectroscopic study of Ce(III) coordination in the 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid containing chloride ion.
abstract: Cyclic staircase voltammetry, controlled potential coulometry, and electronic absorption spectroscopy were used to probe the coordination and accessible oxidation states of Ce(3+) dissolved in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BuMePyroTf(2)N) before and after the addition of chloride ion as BuMePyroCl. Controlled potential coulometry indicated that the oxidation of Ce metal in this ionic liquid produces only Ce(3+). Spectroscopic examination of the resulting solutions indicated that Ce(3+) was weakly solvated by Tf(2)N(-) ions as [Ce(Tf(2)N)(x)]((x-3)-), x ≥ 3. This species can be reduced at negative potentials, probably to a related Ce(2+) species, but the latter is unstable and quickly disproportionates to Ce(3+) and Ce(0); the latter appears to react with the ionic liquid. The addition of Cl(-) to solutions of [Ce(Tf(2)N)(x)]((x-3)-) causes the precipitation of CeCl(3)(s), providing a convenient route to the nondestructive recovery of Ce(3+) from the ionic liquid. However, as the Cl(-) concentration is further increased, the CeCl(3)(s) redissolves as the octahedral complex, [CeCl(6)](3-), and the voltammetric and spectroscopic signature for [Ce(Tf(2)N)(x)]((x-3)-) disappears. Absorption spectroscopy indicated that the bulk controlled potential oxidation of solutions containing [CeCl(6)](3-) produces [CeCl(6)](2-). Although stable on the time scale of voltammetry, this species slowly reacts with the ionic liquid and is converted back to [CeCl(6)](3-).
authors.affiliation: Department of Chemistry and Biochemistry, University of Mississippi, Mississippi 38677, USA.
authors.forename: Li-Hsien
authors.initials: LH
authors.lastname: Chou
authors.forename: Walter E
authors.initials: WE
authors.lastname: Cleland
authors.forename: Charles L
authors.initials: CL
authors.lastname: Hussey