Redox behaviour

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... 

An intrinsic requirement in the design of neutral radical conductors is a low disproportionation energy for reaction 11.5. Electrochemical investigations of the redox behaviour of 1,2,3,5-dithia and... 

Because of possible catalytic and biological relevance of metal-sulfur clusters, several such compounds of cobalt have been prepared. The action of H2S or M2S (M = alkali metal) on a non-aqueous solution of a convenient cobalt compound (often containing, or in the presence of, a phosphine) is a typical route. Diamagnetic [Co6Ss(PR3)6] (R = Et, Ph) comprise an octahedral array of metal atoms (Co-Co in the range 281.7 to 289.4pm), all faces capped by atoms,and show facile redox behaviour... 

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. 

The redox behaviour of transition metal complexes with soft ligands. E. Uhlig, Comments Inorg. Chem., 1981,1,169-182 (43). 

Redox behaviour of this type is considered to influence many substitution reactions of Pt(IV) . ... 

Barranco, E.M., Crespo, O., Gimeno, M.C., Jones, P.G., Laguna, A. and Villacampa, M.D. (1999) Synthesis, structure and redox behaviour of gold and silver complexes with 3-ferrocenylpyridine. Journal of Organometallic Chemistry, 592, 258. 

Burke LD, Nugent PF. 1997. The electrochemistry of gold I The redox behaviour of the metal in aqueous media. Gold Bull 30(2) 43-53. 

Uenishi et al. [95] investigated the redox behaviour of palladium at start up in the perovskite-type structure LaFePdOx. An interesting behaviour is reported due to their self regenerative function, which provides high catalytic performances under cycling... 

Dendrimers are taking their space in the tool box of the modern synthetic chemist. Dendritization might offer solutions to problems yet unsolved. Dendritic wedges, i. e. dendryl substituents of well-chosen size and generation allow us to tune molecular properties like solubility, steric accessability of reactive sites, redox behaviour, and other features. Easy-to-make dendrimers and dendrons will thus become extremely helpful for any chemist in the covalent as well as in the supramolecular world . 

A simple example of the redox behaviour of surface-bound species can be seen in Figure 2.17, which shows the behaviour of a bare platinum electrode in N2-saturated aqueous sulphuric acid when a saw tooth potential is applied. There are two clearly resolved redox processes between 0.0 V and 0.4 V, and these are known to correspond to the formation and removal of weakly and strongly bound hydride, respectively (see section on the platinum CV in chapter 3). The peak currents of the cathodic and anodic reactions for these processes occur at the same potential indicating that the processes are not kinetically limited and are behaving in essentially an ideal Nernstian fashion. The weakly bound hydride is thought to be simply H atoms adsorbed on top of the surface Pt atoms, such that they are still exposed to the... 

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 this chapter, for convenience of discussion, the redox behaviour of cyclic systems is divided into two categories. Initially, those reactions for which there is no marked alteration of the unsaturation pattern of the ligand are discussed. Subsequently, systems in which the final product involves an alteration in the ligand s unsaturation are treated. However, it is emphasized that a continuum exists between redox behaviour which is completely metal-centred and that which is solely ligand-based. 

It needs to be pointed out that E values may also be quite sensitive to the nature of the solvent and supporting electrolyte used for an electrochemical study. Apart from solvation effects of the non-specific type, solvent molecules may occupy coordination sites in either the starting complex or the products and hence influence redox behaviour (Fabbrizzi, 1985). Similarly, the nature of the anion present may also strongly influence the redox potential if it has ligating properties (Zeigerson etal., 1982). Because of such effects, caution needs to be exercised in attempting to compare electrochemical data which have not been obtained under similar conditions. 

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... 

In this chapter, the discussion has centred on the redox behaviour of the cyclic systems of a limited range of metal ions. Nevertheless, the examples are of sufficient breadth to illustrate that the redox behaviour of a particular system usually depends upon a fine balance between kinetic, thermodynamic and structural factors in which both the nature of the central metal ion and of the cyclic ligand are major influences. Of course, such considerations are not restricted to macrocyclic systems - however, the latter have provided convenient models for the elucidation of a variety of redox behaviour - much of which is of relevance to other areas and, for example, to many of the natural redox systems. 

Many model systems which mimic both the redox behaviour [for example, ready reduction to Co(i) species] and the alkyl binding ability of vitamin Bu derivatives have been investigated. The most studied of these has involved bis(dimethylgloximato)cobalt systems of type (307), known as the cobaloximes (Bresciani-Pahor et al., 1985). Other closely related... 

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... 

Electrochemical studies indicate that the redox behaviours of the different derivatives are dominated by the nature of the chalcogen at position 2, with the selenium containing cations more readily reduced (by more than 0.1 V) than the sulfur analogues.82 The difference has been ascribed to the extent of delocalisation of the positive charge away from the heterocycle, onto the fused aromatic ring. 

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