Copper complexes cyclic voltammetry

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

The occurrence of the redox-driven reversible assembling-disassembling process involving copper complexes of 16 has been verified through cyclic voltammetry experiments at a platinum electrode in a MeCN solution. Figure 2.17 shows the CV profile obtained with a solution of the double-strand helicate complex [ Cu 21 (16)212 +. 

The results obtained by cyclic voltammetry clearly show that upon oxidation or reduction of the central metal copper, the macrocycle is set in motion. Upon oxidation of 6(4)+, the resulting tetrahedrally coordinated Cu(II) is unstable as Cu(II) forms stable square planar complexes or higher coordination (five or six). Therefore, the macrocycle pirouettes around the axle permitting the restoration of a stable coordination, that is pentacoordination by the 2,2, 6 2"-terpyridine and 2, 2 -bipyridine... 

The redox properties of dinuclear copper(II) complexes have received extensive attention using cyclic voltammetry measurements, and it was recognized in the early literature that the two copper(II) ions could be reduced to copper(I) at the same potential or at different potentials (Section 53.3.7).30,934,1021,1022 In either case the reduction requires a two electron process and if the E° values are well separated may result in the observation, under favourable circumstances, of a two-peaked cyclic voltammogram (Figure 61b), as in... 

At the end of this section on the relationship between the electronic properties and the stereochemistry of complexes of the copper(II) ion, it is worth summarizing the most useful physical techniques which offer a criterion for the presence of a polynuclear copper(II) complex rather than a mononuclear complex. These are (i) magnetic susceptibility measurements down to near absolute zero, for the determination of O or / values (ii) ESR spectra of magnetically dilute systems, in the solid state or in solution, to obtain hyperfine data and (iii) cyclic voltammetry to show evidence for a one-step reduction process in a Cu2 species. 

Tohnan and Lee constructed a type 1-like site linked to a type 2-like site and investigated the potential for intramolecular electron transfer between the two. Their coordination scheme is illustrated in Figme 6(a) the structure of their complex in shown in Figure 6(b). Cyclic voltammetry showed the two Cu(II) atoms to undergo quasi-reversible, independent reduction with 1/2 values consistent with the two copper atoms coordination -0.911 V for the CuSR site, -0.112 V for the CuPyr one. These studies did not address the question of intramolecular electron transfer between the two sites, however. 

As pointed out some time ago, the electrochemistry of the dicopper complex of the series M2(l,3,5-triketonate)2 (140) posed some problems of interpretation. It was at first thought that the copper(II) complexes should display a single two-electron reduction [Cu(II)—Cu(II) Cu(I)—Cu(I)], with features of chemical reversibility in the short reaction times of cyclic voltammetry . Later, it was stated that they undergo a single two-electron reduction only in the presence of alkali metal ions. In the absence of such cations, the Cu2(l,3,5-triketonate)2 derivatives undergo the stepwise sequence Cu(II)—Cu(II) Cu(II)—Cu(I) Cu(I)—Cu(I), the second one-electron reduction being irreversible and located at rather negative potential values " . ... 

The scheme of Mn2+ ion extrusion from corresponding sarcophaginate has been deduced using UV-vis spectrophotometry, EPR and cyclic voltammetry [179]. The extrusion of the copper ion after its reduction to copper(I) ion is too fast to be examined by cyclic voltammetry, and the kinetics of the reduction of [Cu(sar)]2+ cation to copper(II) [Cu(sar)] complex has been followed by pulse radiolysis over a shorter time using the hydrated electron to probe for extrusion of the metal ion. This reduction process has been registered spectrophotometrically to yield a second-order rate constant. The... 

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],... 

The effect of metal ion stereochemical preference in mediating the final structure of a self-assembling helix was examined by Williams and coworkers using the ligand (20) [26]. The formation of a double-hehcal structure is seen from the reaction of two equivalents of copper(I) and two equivalents of (20) (Figure 8). This structure, with pseudotetrahedral geometry around the metal centers, was found to exist in solution by UV-visible spectroscopy, H NMR and cyclic voltammetry. The double helix does not appear to be the only species existing in solution mononuclear [Cu(20)J+ was observed by H NMR spectroscopy. The H NMR spectrum of the complex between copper(I) and... 

The kinetics and mechanism of oxidation of L-ascorbic acid by some cobalt(III) complexes, " manganese(III) complexes and a copper(II) complex have been studied. Direct-current cyclic voltammetry has been used to investigate the suitability of some ferrocene derivatives as mediators for ascorbic acid oxidation in aqueous solution at low pH. ... 

ABSTRACT. After a brief survey of the different types of natural copper proteins, and their metal-centred main functions, the characteristics of "good" synthetic models are outlined. Electrochemical studies, by cyclic voltammetry and/or differential pulse polarography, of some representative models are overviewed. Recent, unpublished, results on several copper complexes intended to mimick the Type I copper sites are described and briefly discussed. 

As mentioned before, a worthwhile model must possess a good accessibility of both the Cu(I) and Cu(II) oxidation states, and retain in solution not only the bimetallic unit but also any bridging group. To detect whether a proposed model of a Type III copper centre satisfies these requirements many studies on the cyclic voltammetry and/or the differential pulse polarography have been carried out and reported [157-210]. In some cases authors started with a di-copper(II) complex, in some other with a di-copper(I) complex and even eventually with a mixed-valence Cu(II)-Cu(I) dinuclear complex. 

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