Cobalt complexes electrochemistry

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... 

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. 

The correlations are relatively successful for complexes where the charge is delocalized within the molecule and where there are no steric constraints. Even more encouraging are the relatively good correlations observed for cobalt complexes in water where more ligand substitution chemistry occurs However, these measurements were made at the dropping mercury electrode. The purpose of this paper is to excu ine further the effects of solution pH and electrode material upon the electrochemistry of these complexes. 

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. 

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... 

Costa G., Tavagnacco C., Mahajan R. Electrocatalytic dioxygen reduction in the presents of cobalt and rhodium-oximes complexes. Bulletin of electrochemistry 1998 14(2) 78-85. 

The electrochemistry of the polymeric and isomorphous cobalt(II) and nickel(II) methylsquarates was also studied by Iwuoha et al. In aqueous solutions, they found evidence that both the nickel(II) methylsquarate and its cobalt analog were dissociated without any reversible redox processes occurring for the metal ions. However, the cyclic and Osteryoung square wave voltammograms, obtained using a Pt electrode for solutions of these complexes in dimethylformamide and dimethylsulfoxide, contained signals attributable to both ligand-based and metal-based redox processes 142). 

Another cobalt-ferrocenyl complex, whose electrochemistry has been studied, is shown in Scheme 7-20 [119]. 

There have been numerous publications concerning electron transfer processes with the participation of macrobicyclic complexes. Moreover, cobalt(II) and cobalt(III) complexes have received the most attention, presumably due to their availability. Several papers deal with electrochemistry of chromium, ruthenium, rhodium, manganese, nickel, iron, and copper complexes. 

Using electrochemistry in this experiment, you will determine the percentage by mass of ionic halide (X-) in your coordination compound, and calculate which possible cobalt(III) complex has a percentage X- closest to this value. 

In this experiment, the electrochemistry of both [Co(en)3]3+/2+ and [Co(ox)3]3+/2+ will be investigated using cyclic voltammetry, and the standard reduction potential (E°, V) for the [Co(en)3]3+/2+ couple will be measured. For metal complex stability reasons discussed below, it is not possible to use this technique to obtain reduction potentials for the mixed ligand cobalt systems an exercise at the end of this experiment helps to estimate these. The E° values obtained will be important for experiment 5.6, in which outer-sphere electron transfer rate constants between [Co(en)3)]2+ and [Co(en)2)(ox)]+ will be mathematically modeled using Marcus theory. 

F. Bedioui, E. De Boysson, J. Devynck, and K.J. Balkus, Jr, Electrochemistry of Zeolite Encapsulated Cobalt SALEN Complexes in Acetonitrile and DMSO Solutions. J. Chem. Soc., Faraday Trans., 1991, 87, 3831-3834. 

From the electrochemical point of view, an important class of materials is that constituted by aluminosilicates incorporating cobalt, iron, etc., centers. In the case of Fe-based zeolites with Mobil Five structure (FeZSM-5) materials, different forms of iron can coexist. These include isolated ions either in framework positions (isomorphously substituting silicon centers), isolated ions in cationic positions in zeolite channels, binuclear and oligonuclear iron complexes in extra-framework positions, iron oxide nanoparticles (size <2 nm), and large iron oxide particles (FcjOj) in a wide distribution (up to 25 nm in size) located in the surface of the zeolite crystal (Perez-Ramirez et al., 2002). The electrochemistry of such materials will be reviewed in Chapter 8. 

Although there has been a great deal of research concerning how plahnum(II) complexes bind to biological molecules and the hkely mechanism of antitumor activity of these platinum-containing species, far less attention has been paid to the properties of other metal complexes in this arena. Recent attention has fallen on cobalt(II)-Schiff base complexes, as several have been discovered to have promise as antiviral agents. A review of recent work has appeared elsewhere [64], so the topic will not be covered here however, in addition to focusing on recent developments, emphasis is placed on the introduction of the new head unit, 3,6-diformylpyridazine (13), into Schiff-base macrocyclic electrochemistry. 

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