T. Rabockai

The electrochemistry of ferrocene in non-aqueous solvents

Abstract the electrochemical oxidation of ferrocene on Pt in dimethylformamide, ethanol, propylene carbonate and their aqueous solutions was studied at 25°C. The concentration of the supporting electrolyte, NaClO 4 , was varied from 0.1 to 0.5 M . The results show that the electrode process may be described as a quasi-reversible one-electron charge transfer, followed by slow decomposition of the oxidized species.

Electrochemical study of perchlorate reduction at tin electrodes

The electrochemical behaviour of tin in de-aerated sodium perchlorate was studied using potentiodynamic and potentiostatic techniques. Tin behaviour in sodium perchlorate has been complicated unexpectedly by the reduction of the perchlorate anion. It is shown that the reduction process takes place within a potential region comprising the negative side of the double layer region and the positive side of the hydrogen region (−0.7V ≤ E ≤ −1.3V). The presence of oxide on the electrode surface favours the reduction reaction, which may occur in two steps; the formation of basic tin(II) chloride followed by its reduction, producing chloride.

Electrochemistry of organometallic compounds. Part III. Oxidations of methyl derivatives of organocobalt(III) complexes with delocalized electronic structure in dimethylformamide

The influence of the equatorial ligand on the electrochemical oxidation of the compounds [H3CCo(chel)B], where chel is bis (dimethylglyoximato), (DH)2; bis(salicylaldehyde)ethylenediimine, salen; bis(salicylaldehyde) o-phenylenediimine, salophen; bis(salicylaldehyde)cyclohexylenediimine, salcn; bis(acetylacetone) ethylenediimine, bae; and where B is pyridine when chel is (DH2), and dimethylformamide (DMF) when chel represents a Schiff base (salen, salcn, salophen and bae), was studied by means of cyclic voltammetry in DMF, 0.2 M in tetraethylammonium perchlorate, between 25 and −25°C, with a platinum disk working electrode. Absorption spectra in the visible and near ultraviolet regions for these compounds in DMF at 25°C were obtained. The complexes exhibit a reversible one-electron oxidation, at −20°C with scan rates >0.5 V s−; chemical reactions following electron transfer are not detected under these conditions. At slower potential or higher temperatures, the oxidized product decomposes chemically in a solvent-assisted (or nucleophile-assisted) reaction, yielding products which are electroactive in the applied potential range. The behavior of the [H3CCo (DH2)py] derivative is better described as a quasi-reversible charge transfer followed by an irreversible chemical reaction. Experimental evidence suggests that in the case of the [H3CCo(bae)] derivative at −20°C, the reactive -species is pentacoordinated and weakly adsorbed at the electrode surface. The value of E12 and the energies of the first two absorption bands in the visible spectra reveal the ability of the studied complexes to donate and to delocalize electronic charge.

Electrochemistry of organometallic compounds: Part II. Oxidations of alkyl and aryl derivatives of bis(salicylaldehyde)ethylenediimine cobalt(III) in dimethylformamide⋆

Abstract The influence of the axial organic ligand R on the electrochemical oxidation of the compounds [RCo III (salen)DMF)], where salen is bis(salicylaldehyde)ethylenediimine, and R=CH 3 , C 2 H 5 , n-C 3 H 7 , n-C 4 H 9 , s-C 4 H 9 , i-C 4 H 9 , CH 2 Cl, CF 3 CH 2 , c-C 6 H 11 CH 2 , c-C 6 H 11 , C 6 H 5 , C 6 H 5 CH 2 , p -CH 3 C 6 H 4 CH 2 , and p -NO 2 C 6 H 4 CH 2 , was studied by means of cyclic voltammetry in dimethylformamide (DMF), 0.2 M in tetraethylammonium perchlorate (TEAP), at 25 and −20°C, with a platinum disc working electrode. The above-mentioned compounds can be classified according to their electrochemical behavior. (a) The complexes with R=CH 3 , C 2 H 5 , n-C 3 H 7 , n-C 4 H 9 , c-C 6 H 11 CH 2 , and C 6 H 5 undergo a reversible one-electron oxidation in the 10–50 V s −1 potential scan range. At slower scan rates, the oxidized product decomposes chemically. At −20°C, this chemical step is slow, and a reversible one-electron electrochemical oxidation is observed. (b) The compounds with R=CH 2 Cl, C 6 H 5 CH 2 , p -CH 3 C 6 H 4 CH 2 , and p -NO 2 C 6 H 4 CH 2 undergo a quasi-reversible one-electron oxidation at room temperature. At −20°C, the electrochemical process becomes more complex. A following chemical reaction is coupled to the quasi-reversible one-electron transfer. Two reduction peaks are observed. (c) The compounds with R=i-C 4 H 9 , s-C 4 H 9 , and c-C 6 H 11 undergo a reversible one-electron oxidation at −20°C. At room temperature, the irreversible chemical reaction following the electron transfer step is too fast to allow the isolation of the electrochemical step. (d) At −20°C, the derivatives with R=C 2 H 5 , c-C 6 H 11 -CH 2 , and c-C 6 H 11 are adsorbed at the electrode surface. Evidence indicates that the reagent in these reactions is the pentacoordinated species [RCo III (salen)]. A linear free-energy relationship between E 1/2 (for reversible processes) and the Taft polar parameters σ * was obtained with a slope of ϱ * =0.25±0.03. As expected, the benzyl derivatives which present mesomeric effects do not fit this polar correlation. The rate of the electrochemical oxidation is also affected by the nature of the ligand R. For the ligands which are strong electron-withdrawing groups and for the benzyl derivatives, the rate of the electrochemical oxidation of the metal ion decreases at room temperature. At lower temperatures, it is suggested that the oxidation to the Co IV -R species is followed by a chemical reaction in which this complex is partly transformed into a Co III (R · ) species, which is reduced at a much more cathodic potential than the Co(IV) species.

Electrochemical dissolution and passivation of tin in citric acid solution using electron microscopy techniques

Abstract The electrochemical behaviour of tin in 0.5 M citric acid solution was studied by electron microscopy techniques in addition to the potentiodynamic method. The observed electrochemical dissolution is quite similar to pure chemical dissolution when metallographic practices are used and takes place distinctly between the grains. The film growing process follows a dissolution/precipitation mechanism. The local reactivation process occurs primarily along the tin grain boundaries locations.

Electrochemistry of organometallic compounds: I. Cyclic voltammetry of organocobaloximes in aqueous acid solutions

This paper presents a systematic investigation on effects of the nature of the organic axial ligand on the primary electrochemical oxidation steps of organoaquobis(dimethylglyoximato)cobalt(III). Evidence is presented to support a one electron reversible process, yielding a cobalt(III) compound attached to the organic radical. Studies of p-substituted benzyl and phenyl derivatives support further the proposed process. The following step is a pseudo-first order irreversible dissociation of the oxidized species, yielding the trans-Co(DH)2(H2O)+ and the organic radical that can be further oxidized at the electrode. Linear free energy correlations obtained between E1/2 and Taft or Hammett parameters, depending on the nature of the organic substituent in axial position, strongly favor that Co-alkyl(aryl) bonding electrons are involved in the electron transfer.

Cyclic voltammetry of iron dimine complexes in acetonitrile

Abstract The electrochemical behavior of iron diimine complexes, (H3C−N=C(R)−C(R′)=N−CH3)3Fe(II) (R, R′=H,H;H, CH3; CH3, CH3), and (C5H4N−C(R1)=N(R2))3Fe(II) (R1, R2=H, CH3; CH3, CH3) on a platinum working electrode in acetonitrile is described, and compared to that of the parent aromatic complex, tris-(2,2′-bipyridine)Fe(II). One-electron reversible oxidations were found for all the compounds studied. The electrochemical reductions show 2–3 reduction waves in the potential range studied. Only for the complexes of mixed diimine ligands or 2,2′-bipyridine, a pre-adsorption wave is also observed. It is possible to stabilize low valence states with all ligands studied. A formal iron(I) state is described for the first time for all aliphatic diimine complexes, thus showing that the acceptor properties of the diimine complexes do not depend on the presence of the aromatic rings, but on the iron-diimine chromophore.

Electrochemistry of organometallic compounds. Part IV. Oxidations of benzylic derivatives and p-substituted benzylic derivatives of bis(dimethylglyoximato) and bis(salicylaldehyde)o-phenylenediimine cobalt(III) in dimethylformamide

The electrochemical oxidation of some p-substituted benzylic derivatives of Co(III) dimethylglyoximato and Co(III)bis(salicylaldehyde)o-phenylenediimine, in dimethylformamide, 0.2 M in tetraethylammonium perchlorate, on a platinum electrode, at several temperatures, is described as an ECE type, the first electrochemical step being a quasi-reversible one-electron charge transfer at room temperature. At temperatures around −20°C, or lower, the influence of the irreversible chemical decomposition of the oxidized species, via a solvent or other nucleophilic-assisted reaction, is negligible. It is suggested that at low temperatures the oxidation to the formally CoIV-R species is followed by an isomerization reaction in which this complex is partially transformed in a CoIII-(R) species or a π-complex, which undergoes an electroreduction at less positive potentials than those corresponding to the reduction of the CoIV-R species.

The Potentiodynamic Electrooxidation of Glycerol on Platinized Platinum Electrodes

Abstract The electrooxidation of adsorbed glycerol species on platinized platinum electrodes in 1 N H2SO4 was studied by cyclic voltammetry and the potential step method. The main conclusions are: the electrooxidation of glycerol at potentials lower than 1.2 V (vs, RHE) is a complex reaction in which more than one adsorbed intermediates are probably involved. The adsorbed intermediates exhibit ageing effects, at higher potentials a chemical interaction between glycerol and adsorbed oxygen occurs and the overall process is controlled by mass transfer.

Electrochemistry of Europium in Aqueous and Aqueous Formamide Solutions

Abstract The electrochemical behavior of the system Eu(III)/Eu(II) in aqueous formamide solutions was studied by current reversal chronopotentiometry at a mercury pool electrode, in 1 M NaClO4 The results indicate that double layer effects must be considered rather that ion solvation effects when explaining the influence of formamide on the Eu(III)/Eu(II) electrode reaction.