Cobalt, electrochemistry

Electrochemistry and Kinetics. The electrochemistry of the nickel—iron battery and the crystal stmctures of the active materials depends on the method of preparation of the material, degree of discharge, the age (Life cycle), concentration of electrolyte, and type and degree of additives, particularly the presence of lithium and cobalt. A simplified equation representing the charge—discharge cycle can be given as ... 

The electrochemistry of cobalt-salen complexes in the presence of alkyl halides has been studied thoroughly.252,263-266 The reaction mechanism is similar to that for the nickel complexes, with the intermediate formation of an alkylcobalt(III) complex. Co -salen reacts with 1,8-diiodo-octane to afford an alkyl-bridged bis[Co" (salen)] complex.267 Electrosynthetic applications of the cobalt-salen catalyst are homo- and heterocoupling reactions with mixtures of alkylchlorides and bromides,268 conversion of benzal chloride to stilbene with the intermediate formation of l,2-dichloro-l,2-diphenylethane,269 reductive coupling of bromoalkanes with an activated alkenes,270 or carboxylation of benzylic and allylic chlorides by C02.271,272 Efficient electroreduc-tive dimerization of benzyl bromide to bibenzyl is catalyzed by the dicobalt complex (15).273 The proposed mechanism involves an intermediate bis[alkylcobalt(III)] complex. 

Dinuclear clusters ferrous site distortion, 38 175 spin ladder, 38 182-183 Dinuclear cobalt complex, 45 291-293 Dinuclear complexes osmium, electrochemistry, 37 321-323 quadruply bridged, 40 187-235 axial ligand substitution properties, 40 232-234... 

Electrochemistry of Cobalt-containing Species with Inorganic Ligands 531... 

Most of the electrochemistry that deals with cobalt compounds bearing strictly inorganic ligands is of vintage character, so only a brief account of that body... 

Subsequent investigations were undertaken of cobalt corroles with modified structures [77] and with cobalt in higher oxidation states [78]. In addition, cobalt-containing corrole dimers were studied [79], cobalt biscorroles were investigated ]80, 81], the influence of various alkyl and aryl substituents on the electrochemical behavior of cobalt corroles was probed ]82], and the effects of solvents on the electrochemistry of these compounds was examined [83]. 

Finally, some aspects of the electrochemistry of cobalt(II) porphycenes (17) have been discussed in two relatively recent articles ]84, 85]. 

Fig. 8 Scheme of the electrochemical and photochemical conversions involved in the electrochemistry of cobalt hexacyanoferrate films according to Ref 55. 

Cobalt(II) hexacyanoferrate, formally similar to Prussian blue, exhibits a far more complex electrochemistry. Only recently, Lezna etal. [65] succeeded in elucidating this system by a combination of in situ infrared spectroscopy and electrochemistry, and ex situ X-ray photoelectron spectroscopy. Figure 8 shows the pathways of the three different phases involved in the electrochemistry, and their interconversion by electrochemical redox reactions and photochemical reactions. 

Despite some small spectral differences, the similarities have been sufficient to confirm the slow step in the electrochemistry of immobilized cobalt porphyrin mediators (113) and to identify the intermediates involved in a tetrathiafulvalene polymer coated electrode (7). A polyxylylviologen -polystyrenesulfonate co-polymer coated electrode, on the other hand, showed no changes in the position of the peaks in the absorption spectra upon immobilization (111). Presumably this indicated an absence of interactions between neighboring viologen moieties. Similar spectral results have been obtained using photoacoustic spectroscopy (PAS). Heptyl viologen adsorbed on Pt exhibited an unshifted spectrum which correlated with the electrochemical results (115). 

In summary, the electrochemistry of organometallic and metalloporphyrins is dominated by synergistic electron transfer of extramolecular solution components (H20, 02, electrophiles, and nucleophiles). This provides a convenient means for evaluation of the molecular activation (catalytic) properties of these important metal-centered systems. Only in the case of iron (II)- and cobalt(II)-... 

Ozoemena K I, Nyokong T Westbroek P (2003) Self-assembled monolayers of cobalt and iron phthalocyanine complexes on gold electrodes Comparative surface electrochemistry and electrocatalytic interaction with thiols and thiocyanate. Electroanalysis 15(22) 1762-1770... 

Ozoemena KI, Nyokong T (2006) Comparative electrochemistry and electrocatalytic activities of cobalt, iron and manganese phthalocyanine complexes axially co-ordinated to mercaptopyridine self-assembled monolayer at gold electrodes. Electrochim Acta 51(13) 2669-2677... 

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