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-).

A combined quantum mechanical and molecular mechanical Monte Carlo simulation method was used to determine the free energy of binding between tetramethylammonium ion (TMA+) and benzene in water. The computed free energy as a function of distance (the potential of mean force) has two minima that represent contact and solvent-separated complexes. These species are separated by a broad barrier of about 3 kJ/mol. The results are in good accord with experimental data and suggest that TMA+ binds to benzene more favorably than to chloride ion, with an association constant of about 0.8 M-1.

The coordination and accessible oxidation states of Nd and Pr were investigated in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BuMePyroTf2N) by using electronic absorption spectroscopy, cyclic staircase voltammetry, and controlled potential coulometry. These experiments were carried out in the neat ionic liquid (IL) and in the IL containing free Cl(-) from the dissolution of BuMePyroCl. The electrolytic dissolution of Ln = Nd and Pr metal in this IL produces only the respective Ln(3+) ions. These trivalent species can be reduced to Ln(2+), but the resulting divalent species exhibit only transient stability, undergoing rapid disproportionation to Ln(3+) and Ln(0). The intensity of the hypersensitive (4)G5/2 ← (4)I9/2 electronic transition for Nd(3+) dissolved in the IL was substantially larger than it was in noncoordinating solvents such as aqueous HClO4, indicating moderate interactions between Nd(3+) and Tf2N(-) ions, probably resulting in anionic species such as [Nd(Tf2N)x]((x-3)-). The addition of Cl(-) to [Ln(Tf2N)x]((x-3)-) solutions results in the precipitation of LnCl3(s) (s = solid). The LnCl3(s) redissolves to give the octahedral complex [LnCl6](3-) as the Cl(-) concentration is raised further. In the IL containing excess chloride, the (3)P0 ← (3)H4 transition for [PrCl6](3-) exhibits ligand-mediated pseudohypersensitive behavior.

Electrodeposition of the selenium film in 1-ethyl-3-methylimidazolium chloride-tetrafluoroborate ionic liquid containing excess chloride ions on indium tin oxide (ITO) coated glass electrodes was studied at 30 o C. Cyclic voltammogrammetric results indicate that the reduction reaction of Se(IV) to Se (0) is not a simple four-electron reduction. Scanning electron microscopy reveals that the morphology of the selenium deposits is affected by the applied deposition potential and X-ray powder diffraction data indicates the Se deposits is the crystalline of t-Se phase.

Cerium­(IV) is often employed as a surrogate for plutonium­(IV) in investigations involving the processing of spent nuclear fuel and is an important oxidant in organic synthetic reactions. Surprisingly little is known about the chemistry and electrochemistry of cerium­(IV) complexed as [CeCl6]2– in the hydrophobic green ionic liquids that are proposed for these applications such as those based on the bis­(trifluoromethylsulfonyl)­imide (Tf2N–) anion. Of particular interest is its stability in these ionic liquids in the presence of unbound Cl–. Therefore, the homogeneous pseudo-first-order kinetics of the reaction between [CeCl6]2– and Cl– was investigated in the 1-(1-butyl)-1-methylpyrrolidinium bis­(trifluoromethylsulfonyl)­imide (BuMePyroTf2N) ionic liquid as a function of temperature. These measurements revealed that [CeCl6]2– is surprisingly stable, even at elevated temperatures with a half-life of 44 min at 398 K. Although classed as an outer sphere electron transfer process, the [CeCl6]2–/3– redox reaction exhibits mixed control in this ionic liquid. In order to elucidate the origin of this behavior, detailed measurements of the heterogeneous rate of this reaction were carried out in BuMePyroTf2N and in five additional ionic liquids based on the Tf2N– anion with structurally and chemically distinct cations, including 1-(1-butyl)-3-methylimidazolium (BuMeIm+), tri­(1-butyl)­methylammonium (Bu3MeN+), 1-butyltrimethylammonium (BuMe3N+), 1-(1-butyl)­pyridinium (BuPy+), and 1-ethyl-3-methylimidazolium (EtMeIm+) by using electrochemical impedance spectroscopy (EIS). The heterogeneous rate constants of the [CeCl6]2–/3– reaction at a glassy carbon electrode were found to exhibit a near linear dependence on the absolute viscosity of these ionic liquids, indicating that the rate of this reaction may be controlled by solvent reorganization dynamics in these highly viscous ionic liquids in accordance with contemporary predictions of the Marcus theory of electron transfer. Furthermore, the choice of the organic cation can be used to tune the redox potential of the [CeCl6]2–/3– electrode reaction.