FC Redox Processes

The 2+/3+ transition in the Marcus model or its successors involves only small Inner Sphere changes in solvation molecule coordinates in the radial direction to and from the ion. Electron transfer under FC or Born-Oppenheimer conditions demands that an activation energy in the outer Continuum should resist one-electron transfer via a continuum inertial term X = (e2/2r )(l/n2 - l/e0) where r is an effective intermediate reactant-product radius. To avoid error, X can be 

Marcus (Appendix to Ref. 44) suggested substituting a mean differential dielectric constant 3 a/3Aa for Ec(or Ea) as dielectric saturation is approached. 

Because of the small activation energy, the Tafel plots will show considerable curvature. An obvious problem is that the anharmonicity 

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Reactivity ofFc with the IL components generally observed when the anodic potential window of the IL is close to the formal redox potential of Fc° [58,63]. The Em of Fc° redox process differs from the E this effect is related to the inequality in the diffusion coefficients of Fc and Fc in almost all known ILs [25, 46]. 

In contrast to the relative ease of reduction, oxidation of fullerenes requires more severe conditions [113, 114]. Not only does the resonance stabilization raise the level of the corresponding oxidation potential (1.26 V versus Fc/Fc ), but also the reversibility of the underlying redox process is affected [115]. 

Table 6 Formal electrode potentials ( V vs. Fc/Fc+) for the redox processes exhibited by complexes [Co3(dpa)4X2] in CH2Cl2 solution...

An isomeric mixture of the C2v and D3 isomers in TCE displays only two one-electron reduction waves by OSWV. The waves correspond to the 0/—1 and —1/—2 redox processes and overlap at —0.77 and — 1.08 V vs. Fc/Fc+ [60]. The anodic scan, however, shows four oxidation waves, consisting of two pairs of consecutive small and large waves. Each pair has been assigned, on the basis of their currentdntensity ratio, to the two isomers in the mixture, which exist in a 1 5 ratio of C2v D3-C7g (see Table 9) [62]. The assignment of D3-C78 as the easier to oxidize isomer is in agreement with the previously calculated HOMO energies for the two isomers [63]. 

Table 7-28. Formal electrode potentials (vs. SCE) for the redox processes exhibited by the nickel(il) complexes shown in Scheme 7-29 (Fc = (C5H5)Fe(CsH4)]...

Although the mobility of MePc complexes should be strongly reduced in the intracrystalline faujasite supercages, truly site-isolated metal centers can be obtained this way. Moreover, Fc and Mn (salts or exchanged zeolites) which arc active for one-elcctron redox processes as in Fenton free radical H2O2 decomposition (see reaction),... 

This redox process is used as a convenient internal, secondary reference electrode and, therefore, E° is defined as OV for reference purposes. (Relative to the standard hydrogen electrode, °fc+/fc= + 0.40 V.)... 

Many other compounds also have similar solubility properties to Fc and exhibit a reaction scheme analogous to the Fc " case in ionic liquids (see schematic diagram in Fig. 14.5), which allows voltammograms from adhered microparticles to be essentially indistinguishable from that obtained with the dissolved material. Notable examples include Fc derivatives [12, 24, 25, 40], l,3,5-tris(3-((ferrocenylmethyl) amino)pyridiniumyl)-2,4,6-triethylbenzene hexafluorophosphate ([PD] [Pp6]3) [12, 41] and trans-Mn [23]. Thus, voltammetric studies using arrays of adhered solid microparticles are frequently able to provide an efficient method for obtaining the formal potentials of redox processes in ionic liquids. 

Irving-Williams stability order. Supporting data indicated a 2 2 (host/guest) complex stoichiometry in solution with a 1 2 stoichiomefiy in the presence of excess Cu ". Recently, rhodamine-based ferrocene derivatives have been used for cation sensing, for example, system 13 that responds to Cr +, which is an ion involved in various biochemical processes at the cellular level.An unusual anodic shift of —140 mV was observed in the Fc/Fc" " redox potential upon complexation of this cation in ethanol. 

Cyclic voltammetry shows two different redox processes which correspond to the reduction/oxidation of the polypyrrole backbone and the ferrocene moiety, respectively. It also confirms that the concentration of ferrocene in the film can be controlled by varying the composition of the feed. There is less efficient film formation with a higher relative concentration of P-6-Fc because of parasitic current for the oxidation of ferrocene. 

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