Cobalt cyclic voltammetry

Porphyrin, octaethyl-, cobalt complex cyclic voltammetry, 4, 399 <73JA5140)... 

Cobalt, p-pe roxobis(pentaammine)-cyclic voltammetry, 1, 482 Cobalt, tetraammine-structure, 1, 8... 

Two aspects of porphyrin electrosynthesis will be discussed in this paper. The first is the use of controlled potential electroreduction to produce metal-carbon a-bonded porphyrins of rhodium and cobalt. This electrosynthetic method is more selective than conventional chemical synthetic methods for rhodium and cobalt metal-carbon complexes and, when coupled with cyclic voltammetry, can be used to determine the various reaction pathways involved in the synthesis. The electrosynthetic method can also lead to a simultaneous or stepwise formation of different products and several examples of this will be presented. 

Cyclic silylphosphanes, see Silylphosphanes, phosphorus-rich, cyclic Cyclic sulfur-nitrogen compounds, see Sulfur-nitrogen compounds, cyclic Cyclic trithiolate ligand, 38 8-9 Cyclic voltammetry A. chroococcum Fd 1, 38 130-131 fullerene adducts, 44 19 nickel(ll) macrocyclic complexes, 44 112 Rieske proteins, 47 138, 139 Cyclidenes, as cobalt complex ligands, 44 282-284... 

Table 1 lists some of the binding constants and rate constants measured for the reaction of CO2 with redox-active molecules. Various techniques have been used to measure these constants including cyclic voltammetry, pulsed radiolysis, and bulk electrolysis followed by UV-visible spectral measurements. The binding constants span an enormous range from less than 1 to 10 M [13-17]. Co(I) and Ni(I) macrocyclic complexes have been studied in some detail [13-16]. For the cobalt complexes, the CO2 binding constants K) and second-order rate constants for CO2 binding (kf) are largely determined by the Co(II/I) reduction potentials... 

According to [96], electrochemical methods, especially the application of cyclic voltammetry, could be a powerful tool to find suitable catalysts for NO removal from combustion products. Investigation of electrocatalytic properties of vitamin B12 toward oxidation and reduction of nitric oxide was reported in [97]. The catalytic activity of meso-tetraphenyl-porphyrin cobalt for nitric oxide oxidation in methanolic solution and in Nafion film was reported in [98]. 

Later reports (58) have questioned whether the earlier report (55) was correct in concluding that the planar cobalt(II) complex of salen was formed in zeolite Y. The characteristics of the supposedly zeolite-entrapped [Con(salen)] are apparently not as similar to the same species in solution as previously reported. For example, planar [Con(salen)] and its adducts with axially disposed bases are generally ESR-detect-able low-spin complexes (59), and cyclic voltammetry of the entrapped complex revealed a Co3+/Co2+ redox transition that is absent in solution (60). These data, and more recent work (58), indicate that, in the zeolite Y environment, [Con(salen)] is probably not a planar system. Further, the role of pyridine in the observed reactivity with dioxygen is unclear, since, once the pyridine ligand is bound to the cobalt center, it is doubtful that the complex could actually even fit in the zeolite Y cage. The lack of planarity may account for the differences in properties between [Con(salen)] entrapped in zeolite Y and its properties in solution. 

In contrast to the stepwise reduction of [Fe4S4(NO)4], [Fe4Se4(N0)4], and the heterometallic cubanes 19 and 21, cyclic voltammetry of the diiron complex [Fe2(TePh)2(NO)4] showed (52) a single reversible two-electron wave corresponding to reduction to [Fe2(TePh)2(NO)4]2, salts of which were subsequently isolated by chemical reduction. This dianion is a 36-electron species, and hence is isoelectronic with the neutral cobalt complexes [Co2(SR)2(NO)4] (26) it thus lacks an Fe-Fe bond. 

The classical dc polarography of vitamins A, B, B2, B6, BI2, and C, nicotinamide, tocopherols, and naphthoquinones has been reviewed [55]. Other studies have examined in detail the cyclic voltammetry of vitamin B12 employing rapid-scan voltammetry at the DME [90] and the HMDE [91]. Vitamin B12 is complexed with trivalent cobalt ion at the heterocyclic nitrogen atoms. As a result of the complexation, a catalytic hydrogen wave is formed for the compound. In addition to the catalytic wave, a wave corresponding to the reduction of the trivalent cobalt to the monovalent state is observed. 

Reduction potentials for /z-superoxo//z-peroxo-cobalt(III) couples have recently been obtained by cyclic voltammetry.739,740 Decomposition or dissociation of one or the other of the components of the couple, which frustrated measurements by other techniques, may be overcome by the use of fast scan rates. Protonation of the /r-peroxo group stabilizes the complex and EB values are pH dependent below pH 3. A similar stabilization on protonation of the peroxo bridge has been noted in the Ct2+-, V2+- and Eu2+-promoted reduction705 of the [(NHj)5Co(02)Co(NH3)5]4+ ion. The protonated species has Kh 10 dm3 mol-1 at 25 °C.705... 

The complex [Co3(/A3-CPh)2Cp3] (76) (E = E = CPh) is reduced by potassium metal to a radical anion whose ESR spectrum suggests a symmetrical structure with a half-filled orbital constructed from cobalt 3d atomic orbitals. The cation [76]" (E = E = CPh), detected by cyclic voltammetry ( = 0.34 V) and prepared by electrolytic oxidation, has the unpaired electron in a degenerate orbital, and a structural Jahn-Teller distortion is again expected 189). 

The electrochemical behaviour of the macrobicyclic boron-, germanium-, antimony-, and tin-capped iron, cobalt, and ruthenium dioximates has been studied by cyclic voltammetry, polarography, and electrolytic experiments [41, 52, 64, 65, 68, 73, 74, 77, 78, 328-330]. For every metal ion, the dependence of the redox potentials on the electronic characteristics of the substituents in the dioximate... 

When immobilized on polymer surfaces, cage complexes may be utilized for modifications of electrodes. The increase in the electron-transfer rate on such surfaces is governed by two factors a high rate of electron transfer in cobalt clathrochelates and the regular disposition of these complexes on the surface. The properties of immobilized macrobicyclic complexes have been considered in Refs. 94, 410, and 411. Cyclic voltammetry has been used to characterize the incorporation of a range of structurally different d-metal sarcophaginates and sepulchrates into Nafion polymer [412]. 

Due to high biocompability and large surface are of cobalt oxide nanoparticles it can be used for immobilization of other biomolecules. Flavin adenine FAD is a flavoprotein coenzyme that plays an important biological role in many oxidoreductase processes and biochemical reactions. The immobilized FAD onto different electrode surfaces provides a basis for fabrication of sensors, biosensors, enzymatic reactors and biomedical devices. The electrocatalytic oxidation of NADH on the surface of graphite electrode modified with immobilization of FAD was investigated [276], Recently we used cyclic voltammetry as simple technique for cobalt-oxide nanoparticles formation and immobilization flavin adenine dinucleotide (FAD) [277], Repeated cyclic voltammograms of GC/ CoOx nanoparticles modified electrode in buffer solution containing FAD is shown in Fig.37A. 

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. 

FABMS) with a double-helical conformation was formed (Figure 4). Each copper atom possesses a distorted tetrahedral geometry, and the complex was shown to persist in solution by H NMR and cyclic voltammetry. In contrast, when hgand (11) was treated with cobalt(II), a 1 1 complex was formed. The crystal structure reveals that the aggregate is not a double helix, and the cobalt possesses a distorted octahedral geometry [23],... 

One merit of this polymer preparation method is that it allows creation of heterometal polymer chains with the intended sequence.93 The stepwise formation of a heterometal double-layer film [IColFe] was monitored by cyclic voltammetry during film construction (Figure 9.16a). When the bis(tpy)iron complex units were connected to the already prepared bis(tpy)cobalt complex layer, the redox activity of the Fenl/Fen couple appeared without... 

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