Copper complexes cyclic voltammograms

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... 

Fig. 10.3. General electrochemical performance of MPA-Gly-Gly-His modified electrodes for the detection of Cu2+ ions. Cu2+ ions are complexed to Gly-Gly-His in the accumulation process and are electrochemically reduced to Cu(0) to give UPD Cu. (a) Cyclic voltammograms of MPA-Gly-Gly-His modified electrodes in 50 mM ammonium acetate (pH 7.0) and 50 mM NaCl at 25°C at a scan rate of lOOrnVs-1 (i) before accumulation of metal ions and (ii) after accumulation in 46 nM Cu2+ in 50 mM ammonium acetate (pH 7.0) for 10 min. Multiple cycles in the copper voltammogram illustrate stable electrochemistry, (b) Cathodic Osteryoung square wave voltammograms of MPA-Gly-Gly-His modified gold electrodes in 50 mM ammonium acetate (pH 7.0) and 50 mM NaCl (i) before accumulation of metal ions and (ii) after accumulation in 46 nM Cu2+ in 50 mM ammonium acetate (pH 7.0) for 10 min. Reprinted from Ref. [12]. Copyright (2005) with permission from Elsevier.

Figure 3. Cyclic voltammograms of bis-chelate copper complexes (a) [Cu(phen)2] and (b) [Cu(dmbp)2] in CH3CN- n-C4H9)4NC104 (0.1 M), and (c) of copper-catenate Cu.5 in CH3CN for oxidation, in DMF for reduction. Oxidation on Pt, reduction on the hanging mereury electrode.

Thus, the cyclic voltammograms of these complexes demonstrated both oxidation and reduction waves and indicated the formation of uncommon species such as copper(III), nickel(III), nickel(IV), and low-spin iron(III) complexes. The data for manganese(III)- and manganese(IV)-capped complexes showed that it is possible to stabilize the tris-dioximatometalate(II) tetraanions with the different ttnMn or ttnMn caps. 

The electrochemical behaviour in MeCN of the dicopper(I) complex, [Cu(bddh)J CBF ) ) deserves some comments. Since the solid is white and the solution is colourless, the degree of solvation could not be assessed by spectrophotometry. By cyclic voltammetry some signs of slow decomposition were detected changes in peak potentials within a few hours at any scan rate. The cyclic voltammograms of this complex show sharp cathodic and broad anodic peaks, the broadness of which increases with scan rate. This suggests the possible formation of two copper(II) species, by oxidation at close potentials, with subsequent reduction to the same copper(I) species. Whether this is true or not, whether the dinuclear... 

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