Nickel complexes electrochemistry

The IR bands in a number of nickel complexes of triaryl formazans have been assigned by Arnold and Schiele.415 A similar assignment of the electronic bands has been carried out.414 LCAO-MO calculations correlate well with these assignments417 and have been extended to include both inner ligand transitions as well as charge transfer bands and d—d transitions.418 EPR spectra have been used to study the nature of bonding in copper complexes of heterocyclic-containing formazans.419 Metal formazan complexes have also been studied by electrochemistry.283,398 420-422... 

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. 

Gosden, G., Kerr, J.B., Fletcher, D. and Rosas, R. (1981) The electrochemistry of square planar macrocychc nickel complexes and the reaction of Ni(I) with alkyl bromides. Journal of Electrvanalytical Chemistry, 117, 101-108. 

A second type of mechanism would be the reductive or oxidative demetallation of Intermediate metalloporphyrlns, allowing nickel and vanadium to complex. From the electrochemistry of porphyrins, and solution studies Involving oxidizing and reducing... 

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). 

The -diketone ttfs-acac-H 131 has been prepared and the electrochemistry of the nickel(II) complex tran5-Ni(ttfs-acac)2(py)2 has been studied in CH2CI2 solntion . It shows two, almost overlapping, one-electron oxidations at about -1-0.4 V, vs. SCE, followed by a single two-electron oxidation at -1-0.72 V. All the processes have featnres of chemical reversibility and are considered as ttf centred. In particular, the first two electrons should be removed stepwisely from the two ttf units. 

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. 

Although the electrochemistry and the electrocatalytic properties of nickel macrocyclic complexes, phthalocyanines and porphyrins have been well studied in various solvents, few data exist on their special and typical behaviour when electropolymerized films in aqueous alkaline solution. During the last decade, it has been shown that nickel tetraazamacrocyclic complexes (examples shown in Figure 8.20) can be easily deposited onto an electrode surface in alkaline solutions... 

DeLaet DL, Del Rosario R, Fanwick PE, Kubiak CP (1987) Carbon dioxide chemistry and electrochemistry of a binuclear cradle complex of nickel(O), Ni2(.mu-CNMe) (CNMe)2(PPh2CH2PPh2)2. J Am Chem Soc 109 754-758... 

The electrochemistry of the charge and discharge of the positive electrode is quite complex and not well understood, especially, the role that cobalt plays in the active material. For simplicity, lets consider the role of nickel hydroxide in the charge-discharge reaction. 

Thus, on the basis of the spectral data alone we cannot draw a conclusion concerning the preferable dissolution order of the above mentioned elements. However, the absence of absorption peaks of MoClg , NiCl4 , TiCls " complex ions indicates that these elements do not transfer to the electrolyte during the anodic dissolution of steel. This was also confirmed by the results of the chemical analysis of melt samples. From the electrochemistry point of view, the fact that electropositive nickel [30] and molybdenum [31] remain in the anode material points to the electrochemical nature of the corrosion process. The results of the spectroscopy measurements and chemical analysis were confirmed by X-ray microanalysis - the electrode surface after 2 h of anodic dissolution was slightly depleted in iron and chromium and was enriched in nickel. 

Using a stoichiometric amount of 22, i.e. six equivalents, afforded a mixture of mono- to hexa-alkylated species from which the ligand 23 was isolated by crystallization. The hexa-alkylation process could be enhanced reacting a twofold excess of 22 with the hexaphenol. The ligand CTV(bipy)6 was then isolated in 71 % yield. Again, the H-NMR provided evidence for the hexasubstitution and the Cat, symmetry of the isolated ligand. The compound obtained can accommodate either three square planar (copper(II)) or tetrahedral (copper(I)) transition metals, or, two octahedral transition metals (nickel(II)). The corresponding complexes are of interest in order to study, metal-metal interactions either by electrochemistry, EPR or photochemistry [39]. 

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