Electrochemical wave splitting

As stated above, electrochemical wave splitting in itself cannot be actually considered as a manifestation of wire-like properties. However, some spectacular or intriguing examples deserve to be quoted. 

The apparent character of many-electron processes, and thus the experimental possibility to observe the one-electron electrochemical steps, depends on the stabilities of the LVls, either thermodynamically or kinetically defined. A process should appear as raie-stage many-electron one at low stabilities of LVls and will split into sequential reactions at higher stabilities. The intermediate region exists where the overall process is represented by one distorted electrochemical wave in an electrochemical curve. Thus, the discussion on one- or many-electron electrochemical steps is becoming of quantitative rather than qualitative nature. 

There is another characteristic value of the stability where the apparent process splits into a series of sequential one-electron steps. Between these thresholds, a rather wide range of stability lies where a process manifests itself as an electrochemical wave with specific distortions. 

The electrochemical features of the next higher fullerene, namely, [70]fullerene, resemble the prediction of a doubly degenerate LUMO and a LUMO + 1 which are separated by a small energy gap. Specifically, six reversible one-electron reduction steps are noticed with, however, a larger splitting between the fourth and fifth reduction waves. It is important to note that the first reduction potential is less negative than that of [60]fullerene [31]. 

The electrochemical behavior of the C70 solvent-cast films was similar to that of the C60 films, in that four reduction waves were observed, but some significant differences were also evident. The peak splitting for the first reduction/oxidation cycle was larger, and only abont 25% of the C70 was rednced on the first cycle. The prolate spheroidal shape of C70 is manifested in the II-A isotherm of C70 monolayers. Two transitions were observed that gave limiting radii consistent with a transition upon compression from a state with the long molecnlar axes parallel to the water snrface to a state with the long molecnlar axes per-pendicnlar to the water surface. 

Thin-film ideal or Nemstian behavior is the starting point to explain the voltammetric behavior of polyelectrolyte-modified electrodes. This condition is fulfilled when (i) the timescale of the experiment is slower than the characteristic timescale for charge transport (fjD pp, with Ithe film thickness) in the film, that is all redox within the film are in electrochemical equibbrium at any time, (ii) the activity of redox sites is equal to their concentration and (iii) all couples have the same redox potential. For these conditions, anodic and cathodic current-potential waves are mirror images (zero peak splitting) and current is proportional to the scan rate [121]. Under this regime, there exists an analytical expression for the current-potential curve ... 

Cyclic voltammetry of 5 and 6, in a 0.1 M tetrabutylammonium hexa-fluorophosphate solution in methylene chloride V5. the ferrocene/ferrocenium reference, reveals two two-electron oxidations ( 1/2 = 200 mV, 1000 mV) and two one-electron reductions ( 1/2 = —H60mV, —ISOOmV). The splitting in the reduction waves, A , is 340 mV, and corresponds to a comproportionation equilibrium constant of 5.6 x 10. The total electrochemical splitting reflects both the electronic interactions typical of a strongly electronically coupled... 

The Cu-+ to Cu reduction, however, appears as a relatively complicated process, as denoted by peak splitting observed in square-wave voltammetric experiments, as shown in Figure 5.7. Here, peak splitting features are significantly sensitive to variations in the square-wave frequency (i.e., in the timescale) of the voltammetric experiment, thus denoting that different electrochemical pathways are probably involved. 

Optical spectroscopic studies on the species [Ru(12S3)2] (Table 3) yield a value of A, the ligand field splitting, 29570 cm S little different from that of the 9S3 analogue (30760 cm ). Despite the close similarity in electronic spectra, the two complexes differ appreciably in their electrochemical behavior. Cyclic voltammetry shows a quasi-reversible one-electron wave for the [Ru(12S3)2] couple [121], at a potential 230 mV less oxidizing than in [Ru(9S3)2] (Eq. 18b Table 2). 

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