Redox behaviour oxidations

In view of the facile oxidation of 10.13a-c it is not surprising that some metathetical reactions with metal halides result in redox behaviour. Interestingly, lithium halides disrupt the dimeric structures of 10.13a or 10.13c to give distorted cubes of the type 10.14, in which a molecule of the lithium halide is entrapped by a Ei2[E(N Bu)3] monomer. Similar structures are found for the MeEi, EiN3 and EiOCH=CH2 adducts of 10.13a. In the EiN3 adduct, the terminal... 

The redox behaviour of Th, Pa and U is of the kind expected for d-transition elements which is why, prior to the 1940s, these elements were commonly placed respectively in groups 4, 5 and 6 of the periodic table. Behaviour obviously like that of the lanthanides is not evident until the second half of the series. However, even the early actinides resemble the lanthanides in showing close similarities with each other and gradual variations in properties, providing comparisons are restricted to those properties which do not entail a change in oxidation state. The smooth variation with atomic number found for stability constants, for instance, is like that of the lanthanides rather than the d-transition elements, as is the smooth variation in ionic radii noted in Fig. 31.4. This last factor is responsible for the close similarity in the structures of many actinide and lanthanide compounds especially noticeable in the 4-3 oxidation state for which... 

BaAn" 03 (An = Th Am) all have the perovskite strueture and are obtained from the aetinide dioxide. In aeeord with normal redox behaviour, the Pa and U eompounds are only obtainable if O2 is rigorously exeluded, and the Am eompound if O2 is present. Aetinide dioxides also yield an extensive series of nonstoiehiometrie, mixed oxide phases in whieh a seeond oxide is ineorporated into the fluorite lattiee of the An02. The UO2/PUO2 system, for example, is of great importanee in the fuel of fast-breeder reaetors. 

A major concern of this review is the tailoring of the redox behaviour of organic compounds, i.e. the optimization of such systems for electron storage and electron hopping. While the emphasis is on reduction and thus on anion formation, it has been shown on many occasions that oxidative cation formation leads to analogous conclusions (Meerholz and Heinze, 1990 Lewis and Singer, 1965). The structure of this text is thus obvious. 

In the promotion of less-common oxidation states, much attention has been focused on the redox behaviour of transition metal ions such as nickel and copper although many other metal types have also had unusual oxidation states stabilized by macrocyclic ligands. However, within the limitations of a single chapter it is not possible to attempt a wide ranging... 

The ability of thioether macrocyclic complexes (and especially those of [9]aneS3) to support multi-redox behaviour at the coordinated metal centre is particularly notable. This allows a series of reversible stepwise one-electron oxidation and/or reduction processes, and stabilization of highly unusual transition metal oxidation states e.g. mononuclear [Pd([9]aneS3)2]2+/3+/4+,149 [Au([9]aneS3)2]+/2+/3+,150 [Ni([9]aneS3)2]2+/3+,151 and [Rh([9]aneS3)2]+/2+/3+.152 It appears to be the ability of the crown thioethers to readily adjust their... 

Interestingly, the isostructural Co(II) dication [Co(L)2]2+ (Ar = C6H4-p-OMe) displays a rather different redox behaviour. In fact, as illustrated in Figure 59, it undergoes either a one-electron oxidation (E2+/3+ = +0.01 V vs. Fc/Fc+), or two separated one-electron reductions ( 2+/+ = -0.93 V E+jq = —1.92 V), the first of which occurs at notably less negative potential values than the above-mentioned ligand-centred processes.11013... 

Complementary to the redox behaviour of the series [Ru3C18(PR3)4], the extra electron present in [Ru3C16(PR3)6] + causes the occurrence of two reversible one-electron oxidations and a reversible one-electron reduction, Table 5.29... 

For the related compounds, phenothiazine and phenoxazine, the reduced form is stable under ambient conditions and oxidation occurs in two one-electron steps. A comparison between the redox behaviour of the two compounds is best made in an antimony trichloride medium where both the radical-cation and the dication levels are stable (Scheme 6.9) [225]. In perchloric acid, phenothiazine shows reversible... 

Several other organic systems have been stndied as potential electrochromes because of their redox behaviour. These include carbazoles, methoxybiphenyls, fluorenones, benzoquinones, naphthaquinones and anthraqninones, tetracyanoquinodimethane, tetrathiafnlvalene and pyrazolines. ° Of particnlar interest are the 1,4-phenylenedi-amines, which form highly colonred species on oxidation. These, known as Wurster s salts, exemplified by Wnrster s Bine (1.97), are anodically colouring and this type of material has found nse in composite electrochromic systems for car rearview mirrors (see 1.5.4.1). 

To understand these complex catalysts we describe some basic HTSC (high Tc) oxides and the important role played by EM in elucidating the nanostructure and chemistry of these complex oxides. The redox behaviour of Cu in various oxidation states of HTSC may be important in environmental control catalysis. 

Review work for future updates of our data base should focus on iron compounds and complexes. The iron system is thought to be of crucial importance for characterizing the redox behaviour of radioactive waste repositories. Preliminary applications have indicated that the lack of data for the iron system is a source of major uncertainties associated with the definition of an oxidation potential. Hence, there is little use in developing sophisticated redox models for radionuclides as long as the dominant redox processes in a repository are poorly known. 

One oxochromium(V) complex, CrO(TETMC), containing the trinegative anion of a corrole (279), has been characterized as the solid.1266 It is prepared (Table 102) simply by exposure to air of a solution presumably containing a Cr11 complex. Aerial oxidation of Cr (TPP) produces the oxochromium(IV) complex CrO(TPP) so the corrole ligand apparently facilitates autoxida-tion. The redox behaviour of CrO(TETMC) has been examined by cyclic voltametry.1267... 

As the HiPIPred and Fdox forms are experimentally indistinguishable in terms of the cluster, it is clear that their redox behaviour must be controlled by the protein, which prevents further oxidation of Fdox or further reduction of HiPIPred. No single iron-sulfur protein is known which... 

Voltammetric sensors Here, detection is based on the redox behaviour of the analyte on the electrode. However, when the analyte is bound to suspended particles or present in complexes that are chemically inert, direct determination is generally not possible. Therefore, voltammetric sensors provide information on the species that are chemically available (labile). Uniquely, these sensors typically involve a necessary preconcentration step in which the analyte is usually reduced and accumulated for a certain time at the electrode. This process is followed by its oxidation and stripping from the electrode. Whole family of methods has emerged based on the different potential-current profiles for the stripping step, all having common name Stripping Analysis (SA). 

Another way to assess ion channel conductance is to use artificial phospholipid vesicles (liposomes) as cell models. These structures (described in more detail in the next chapter) are commonly used to transport vaccines, drugs, enzymes, or other substances to target cells or organs. The vesicles, which are several hundred nanometres in diameter, do not suffer from interference from residual natural ion channel peptides or ionophores, unlike purified natural cells. A liposome model was used to test the ion transport behaviour of the redox-active hydraphile 12.36. The compound transports Na+ and the process can also be monitored using 23Na NMR spectroscopy.26 The presence of the ferrocene-derived group in the central relay allows the ion transport to be redox-controlled - oxidation to ferrocinium completely prevents Na+ transport for electrostatic reasons. Some representative data from a planar bilayer measurement is shown for hydraphile 12.36 in Figure 12.16. 

Hoang, et a1. (2003), Redox Behaviour of La-Cr Compounds Formed in Cr0x/La203 Mixed Oxides and Cr0x/La203/Zr02 Catalysts , Applied Catalysis A General, 239, 95-110. 

The electrochemistry of a number of such six-coordinate compounds [MnXL]+ and seven-coordinate compounds [MX2L] (with L = (203), R,R = Me and X = halide, water, triphenylphosphine oxide, imidazole, 1-methylimidazole or pyridine) has been investigated.551 The redox behaviour of these compounds was of interest because it was considered that the potentially -acceptor macrocycle (203 R = R = Me) may promote the formation of Mn° or Mn1 species or may yield a metal-stabilized ligand radical with the manganese remaining in its divalent state. For a number of macrocyclic ligand systems, it has been demonstrated that the redox behaviour can be quite dependent on axial ligation it was also of interest to study whether this was the case for the present systems. 

Several studies2206-2210 have been published on the redox behaviour of [Ru(S2CNR2)3], A one electron reversible reduction to [Ru(S2CNR2)3]- is observed but the one electron oxidation is... 

Iron-sulfur chemistry has developed over recent years to become a very rich area. A feature of many complexes is their redox behaviour, with more than one oxidation state being important. This... 

The compounds of Nd, Gd-Er, Lu, and Y are stable to around 100 °C the La, Pr, and Sm compounds decompose at 0, 40 and —30 °C, respectively. The compounds of Ce, Eu, Tm, and Yb could not be isolated. This cannot be explained simply by steric effects or redox behaviour of the metals (i) compounds can be isolated with quite large early metals (Nd, Gd) but not with small ones like Yb (ii) the compounds formally involve metals in the (0) state, so metals like Eu and Yb would have been expected to be successful in supporting low oxidation states. Steric factors may have their place, as the compounds of the earlier lanthanides (La-Pr) are less stable than might be expected, possibly because the ligands may not be bulky enough to stabilize the lanthanide atom against decomposition pathways. 

Fomasiero P., Kaspar J., Graziani M., Redox behaviour of high surface area Rh-loaded Ceo jZro jOj mixed oxide. J. Catal. 167 (1997) pp.576-580. 

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