Three-electron reduction processes

Obtained in MeCN solution containing 0.2 mol dm-3 B114NBF4 as supporting electrolyte. Solutions were 2 x 10-3 mol dm 3 in ligand, and potentials were determined with reference to SCE. Three-electron reduction process as determined by coulometric experiments. Cathodic shift in reduction potential produced by the presence of anions (4 equiv) added as their ammonium of butylammonium salts. Values obtained in DMSO solution. 

The triply branched compound 56+ shows a reversible three-electron reduction process and, at more negative potential, a process strongly affected by electrode adsorption. A comparison with the behavior of dumbbell 34+ enables to assign these processes to the simultaneous first and second reduction of its three bipyridinium units. 

Three-electron reduction process as determined by coulometric experiments. 

The first attempt to construct a dendrimer with an electroactive Ru-polypyridi-ne core was based on the reaction of Ru(bpy)2Cl2 with a branched polyether-substituted phenanthroline ligand (11) [27]. In the potential window +2/-2V, this compound shows a one-electron oxidation process and three distinct one-electron reduction processes that, by comparison with the behavior of the... 

While the first electrochemical reduction potential provides an estimate for Ac (assuming it is a reversible process), the second and higher reduction potentials do not provide the spectrum of single electron affinity levels. Rather, they provide information about two-electron, three-electron, and higher electron reduction processes, and, therefore, depend on electron pairing energy. Thus, the utility of solution-phase reduction potentials for estimating solid-state affinity levels is... 

Unlike in CV, pairs of current measurements are made on each period of the square wave. These are at time forward late in the forward pulse, named /forward, and frevere in the reverse pulse, named Iteveix- Both tformad and Reverse are much greater than the time for fully charging the electrode capacitance, so that only the Faradaic current is recorded. With calculation of /net, the difference between /forward and /reverse, SWV presents three types of peak-shaped I-E relations. Figure 65 displays the SWV of a reversible one-electron reduction process. 

As expected on the basis of the presence of an Fe3S4 and an Fe4S4 cluster the response displays multiple redox processes. As a matter of fact there are three consecutive reduction processes, namely A, B and C, with characteristics of chemical reversibility. The processes A and B involve one-electron additions, whereas process C is a two-electron step. Processes A and C are assigned to the Fe3S4-centred reductions [3Fe-4S]+/0 and [3Fe-4S]0/2-, whereas the central system B is assigned to the Fe4S4-centred reduction [4Fe-4S]2+/+. The redox potentials (vs. NHE) for these processes are ... 

U(III) species and a second three-electron reduction to give U(0) metal. The first reduction, U(IV)/U(III) couple, is elec-trochemically and chemically irreversible except in hexamethylphosphoramide at 298 K where the authors report full chemical reversibility on the voltammetric timescale. The second reduction process is electrochemically irreversible in all solvents and only in dimethylsulfone at 400 K was an anodic return wave associated with uranium metal stripping noted. Electrodeposition of uranium metal as small dendrites from CS2UCI6 starting material was achieved from molten dimethylsulfone at 400 K with 0.1 M LiCl as supporting electrolyte at a platinum cathode. The deposits of uranium and the absence of U CI3, UCI4, UO2, and UO3 were determined by X-ray diffraction. Faradaic yield was low at 17.8%, but the yield can be increased (55.7%) through use of a mercury pool cathode. 

The [Co(mnt)2f ( = 1, 2, 3) redox series was reexamined with the aid of ESR by Vlcek and Vlcek.101 Upon chemical or electrochemical oxidation of [Co(mnt)2]2-, an initial spin-triplet monomer [Co(mnt)2] formed. Slow dimerization led to the final oxidation product [Co(mnt)2]2 , which in the solid state or in noncoordinating solvents was diamagnetic. Solution spectra in DMSO showed an ESR signal due to [Co(mnt)2] THF solution spectra were identical but indicated three times less monomer concentration. A THF solution of [Co(mnt)2]2- underwent a reversible one-electron reduction process localized on the metal to yield a green solution of a Co1 complex, [Co(mnt)2]3-, with no ESR signal. 

The analogous uranium(III) compounds also show unusual reactivity patterns. For example, addition of COT to (Cp )3U yields a mixed metallocene dimer (18) bridged by a COT ligand in this reaction, the (Cp )3U complex has effectively acted as a formal three-electron reductant (equation 3)." A variety of substituted (Cp )3U complexes form adducts with CO and CNR (isocyanides) - these are rare examples of actinide metals with r-acidic ligands." Paramagnetic uranium alkyl complexes are active in a range of catalytic processes." ... 

Fe to Fe is a three-electron reduction the standard reduction potential for the process is found from the corresponding value of AG° ... 

There are 32 microscopic formal potentials for the redox process of the tetra-heme protein, cytochrome C3, and the deconvolution of these microscopic states distributed over 110 mV is impossible using electrochemical techniques. Many heme-methyl signals are observed separately, e.g. each heme of cytochrome C3 has four methyl groups so that 80 three-proton intensity signals originating from the 16 heme-methyl groups would be expected in the course of a four-electron reduction process. The microscopic formal potentials of the 32 redox processes can be calculated from the chemical shifts of each heme-methyl group at the five macroscopic oxidation states [125, 127]. The results are shown in Table 6 and the macroscopic formal potential can be deduced from these results. 

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