Electron reversibility

Research and development efforts have been directed toward improved ceU designs, theoretical electrochemical studies of magnesium ceUs, and improved cathode conditions. A stacked-type bipolar electrode ceU has been operated on a lab scale (112). Electrochemical studies of the mechanism of magnesium ion reduction have determined that it is a two-electron reversible process that is mass-transfer controUed (113). A review of magnesium production is found ia Reference 114. 

Complexes (690) undergo two one-electron reversible reductions and two oxidations, all of which appeared ligand centered. Thus, these ligands behave electrochemically much like... 

Mixed-metal dendrimers containing up to 6 Pt(IV)-based organometallic species in the branches and 12 peripheral ferrocene units (8) have recently been synthesized and their electrochemical behavior investigated [13]. As in the previously discussed examples, multi-electron reversible oxidation processes, assigned to the equivalent, non-interacting ferrocene units, have been observed. The authors point out that cyclic voltammetry is a powerful tool to support the structure of the dendrimers containing ferrocene units. 

FIGURE 1.30. Reductive cycle voltammetry of lrcm.y-2,3-dinitro-2-butene in 83-17 acetonitrile-water (+0.1 M Bu4PF6) at room temperature at 0.5 V/s and structural characteristics of the three oxidation states. Dotted curve, one-electron reversible wave centered at the same °. Adapted from Figure 4 in reference 73, with permission from Elsevier. 

Further increase in 2 restores reversibility progressively. The wave eventually becomes a full one-electron reversible wave, with, however, a negatively displaced peak potential corresponding to a new standard potential which corresponds to the standard potential of the C/B couple ... 

Solutions were 2 x 10-3 mol dm-3 in compound, and potentials were determined with reference to the SCE, b Three-electron reversible oxidation process. Two-electron reversible oxidation process. Separation between anodic and cathodic peak potentials values for ferrocene under identical conditions ranged from 80 to 90 mV. Shift in respective ferrocenyl oxidation potential produced by presence of guest cation (2 equiv) added as their thiocyanate salts for potassium and ammonium, and their picrate salts for methylammonium and phenethyl-ammonium. 

Data were obtained in aqueous solution containing 0.2 mol dm"3 KC1 as supporting electrolyte. Solutions were 3 X 10 3 mol dm"3 in compound and potentials were determined with reference to SCE at 21 1°C at 50 mV s"1 scan rate. The solution pH was adjusted with 0.5 mol dm"3 KOH and 0.1 mol dm"3 HC1. 6For [28], [29], [30] and [31] the CVs were reversible one electron oxidations at pH < 6. At pH = 11, an EC mechanism was observed for [28], [29] and [31]. Minor oxidation waves of the amino groups appeared after that of the Fc+/Fc couple at slow scan rate. The CV of [32] was a one-electron reversible oxidation wave, less dependent on the solution pH, and showed no oxidation of the amino groups in the pH range explored. Anodic shifts of anodic current peak potential of the Fc+/Fc couple produced by the presence of metal cations (1 or 2 equiv added as their perchlorate salts). 

In fact, the latter displays a first (one-electron) reversible reduction followed by a second irreversible reduction that in turn shows, on the reverse scan, the oxidation peak of the Rh(I)-dimethylfumarate complex, Figure 21b. The complete interconversion process is illustrated in Scheme 10. 

Similarly, aliphatic thiones are also readily reduced at microcathodes in DMF. Thus, thiocamphor exhibits a one-electron reversible step at —1.88 V versus SCE, which is about 0.9 V more positive than the potential of the reduction of camphor under the same experimental conditions. q , 8-unsaturated thiones such as (18) were also investigated polarographically in pro-tic media. Similarly [179-182], reduction of Q , 8-ethylenic ketones and aldehydes in acidic media yielded dimers. 

One-electron reversible reduction of triarylphosphine sulfides in DMF/Et4NI leads to an anion radical [198, 203, 204]. The second step of the reduction, occurring at slightly more negative potentials, results in different products of cleavage of P—S or P—C bonds - triphenylphosphine, benzene, and diphenylthiophosphinic acid (Scheme 42). 

The electrochemical oxidation of Ti" as Ti(AlCl4)2 in AlClg-NaCl melts (160—330°C) has been shown to proceed in two one-electron reversible steps, as Ti" Ti" Ti. ... 

Attaching a Ceo cluster to an [Ru(bpy)3] + core has been achieved by 1,3-dipolar cycloaddition of azomethine ylides to the fullerene. The electrochemistry of the complex is complicated a one-electron reversible oxidation of the Ru center, five one-electron reversible reductions associated with the Ceo cage, and five more reversible reductions centered on the bpy ligands. The photophysical properties of the complex have been discussed. ... 

With stringent precautions to avoid the presence of water, polycyclic aromatic hydrocarbons show two one-electron reversible waves on cyclic voltammetry in dimethylformamide (Table 7.1). These are due to sequential one-electron additions to the lowest unoccupied molecular n-orbital [1]. Hydrocarbons with a single benzene ring are reduced at very negative potentials outside the accessible range in this solvent. Radical-anions of polycyclic aromatic hydrocarbons [2] and also alkyl benzenes [3] were first obtained by the action of alkali metals on a solution of the hydrocarbon in tetrahydrofuran. They have been well characterised by esr spectroscopy. The radical-anions form coloured solutions with absorption bands at longer wavelength than the parent hydrocarbon [4,5]. 

For the sake of simplicity, the search for additive effects has oriented most of the research, and ligand additivity has been clearly recognized in some cases for many years. Hence, for the series of closely related 18-electron octahedral complexes [Mn(CO)6 x(CNR) ,]+ (x = 1-6) that undergo a single-electron reversible oxidation, the oxidation potential was shown to correlate linearly with the HOMO energy, a... 

Coming to the comparison of the and 0-2 series, the possibilities of isomerization and/or decomposition of the precursor lacunary complexes and, presumably, of their metal ion-substituted derivatives, make it necessary to insure first that no fast conversion occurs, in particular from the a structure to the 2 one. Figure 13(a) compares the cyclic voltammograms of the two lacunary complexes in the pH 3 medium. The main difference appears on the third redox system a single two-electron, reversible wave is obtained for the complex in contrast, the corresponding system for the U2 isomer is clearly constituted by two. 

Ivanov and Kaplun [76] used catechol in the determination of vanadium by adsorptive stripping voltammetry. It has been shown that the studied electrode process comprised one-electron reversible reduction of vanadium (IV) triscatecholate, previously accumulated at the electrode. It has also been found that the reduced... 

Fig. 3.24 Theoretical variation of the (ipa /ipa) ratio with the molar fraction of oxidized form in CVs for a one-electron reversible couple initiated at the formal electrode potential of that couple in the anodic direction for solutions containing different molar fractions of the oxidized form using the base line after (A) and before (B) the anodic peak [205]...

Some organic compounds undergo multi-step one-electron reversible reductions. As shown in Fig. 8.13, buckminsterfullerene (C6o) in AN/toluene at -10°C... 

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