W. E. Cleland

Electrochemical and Spectroscopic Study of Ce(III) Coordination in the 1-Butyl-3-methylpyrrolidinium Bis(trifluoromethylsulfonyl)imide Ionic Liquid Containing Chloride Ion

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 voltammetric investigation of the reactions between surface-confined amines and quinones on gold electrodes: evidence for imine formation

Abstract A surface-confined layer containing naphthoquinone was prepared by reacting 2,3-dichloronaphthoquinone with the amino tail groups of an aminoethanethiolate-modified vapor-deposited gold surface; this surface layer was then reacted with β -ferrocenylethylamine. These modified gold electrodes were examined with cyclic staircase voltammetry in aqueous HClO 4 at the completion of each step in this sequence of reactions. The voltammetric signature for the 2e − , 2H + reduction of the quinoid redox centers disappeared after the ferrocene compound was reacted with the naphthoquinone surface layer; furthermore, the surface coverage of ferrocene was twice that expected on the basis of a 1:1 reaction between the surface-bound naphthoquinone and β -ferrocenylethylamine. These results suggest that the latter reacts with the naphthoquinone carbonyl groups to form a surface-confined di-imine, which cannot be reduced within the electrochemical potential window of aqueous HClO 4 . In similar experiments, 2-[4′-( β -ferrocenylethylaminocarbonyl)phenyl]-1,4-naphthoquinone and 2-[2′-( β -ferrocenylethylaminocarbonyl)ethyl]anthraquinone were synthesized and reacted with aminoethanethiolate-modified gold surfaces. When examined at a platinum electrode in nonaqueous solvents, both of the freely diffusing compounds exhibited two pairs of voltammetric waves characteristic of quinoid and ferrocene functionalities. However, only the ferrocene redox centers of the resulting surface-confined layers were electroactive, suggesting that the reaction of these compounds with the surface-confined aminoethanethiolate involves conversion of the quinoid carbonyls to imines.

A comparative electrochemical study of the coadsorption of bis-[10-(ferrocenylcarbonyl) decyl] disulfide and 10-ferrocenylcarbonyldecanethiol with linear alkane disulfide and alkanethiol compounds on vapor-deposited gold surfaces

Abstract The competitive adsorption of bis-[10-(ferrocenylcarbonyl)decyl] disulfide (I) with n-octanethiol, n-dodecanethiol and n-hexadecanethiol, and with di-n-dodecyl disulfide and 10-ferrocenylcarbonyldecanethiol (II) with n-dodecanethiol was investigated on vapor-deposited gold films in acetonitrile solutions. The resulting self-assembled monolayers were probed in aqueous HClO 4 using cyclic voltammetry. Adsorption isotherm data for all the compounds examined in this study were in good agreement with the coupled Langmuir isotherm model recently proposed by Rowe and Creager. Electrochemically identical mixed monolayers with the same (within experimental error) equilibrium surface coverage Γ Fc of ferrocenyl thiolate were obtained from solutions of I + n-dodecanethiol, I + di-n-dodecyl disulfide and II + n-dodecanethiol, provided that the mole fraction of ferrocene moieties X Fc was the same in each coating solution. In addition, there was no discernible difference in the global adsorption Gibbs energy term of the Langmuir isotherm model for the three mixtures described above.