Relative Stabilities of Oxidation States

In Fig. 30, the cyclic voltammograms of two clusters are compared in Mc2SO solutions. Cluster 59, containing a conventional monodentate uninegative substituent at the singular site, reduces at = -0.97 V ([Fe4S4] ) and shows an irreversible oxidation. On the other hand. 

Redox Potentials of Five-Coordinate [4Fe-4S] Clusters in Me2SO 

Potentials of the [4Fe-4S] and [4Fe-4S] couples could be increased by one or more of these factors (a) reduction of cluster net charge  

None of the preceding factors has yet been examined for the [4Fe-4S] couple, which has not been established in proteins, and, for synthetic clusters, occurs at very negative potentials and is frequently irreversible. It is one of the two candidates for the p /pox couple of nitrogenase (Fig. 

Conceivably, the [4Fe-4S] potential could be shifted in the negative direction by effects of the type operative in the clusters in Table IV. In a study of the oxidation of the dithionite-reduced FeMo protein of K. pneumoniae, however, the first EPR-observable event is removal of electrons from P-clusters to afford a spectrum typical of the [4Fe-4S] (5 = 

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Apart from its own susceptibility to oxidation or reduction, a solvent can affect redox equilibria by modifying the relative stabilities of oxidation states of solutes. Thus Cu+ is unstable in aqueous solution to disproportionation (Section 5.4) but it is quite stable in acetonitrile. This arises from the relative magnitudes of the solvation energies and entropies of Cu+ and Cu2+ in the different solvents. In ammonia, cobalt(III) is much more stable relative to cobalt(II) than in water. The... 

The knowledge of the relative stability of oxidation states, i.e., redox potentials, is very important for a chemical application. Trends in the stability of various oxidation states of the very heavy elements were predicted earlier on the basis of atomic relativistic DF and DS calculations in combination with some models based on a Born-Haber cycle (see [12]). The conclusions were, however, not always unanimous and varied depending on the model. Later, this topic received a more detailed consideration... 

With iron the trends already noted in the relative stabilities of oxidation states continue, except that there is now no compound or chemically important circumstance in which the oxidation state is equal to the total number of valence shell electrons, which in this case is eight. The highest oxidation state known is VI, and it is rare. The only oxidation states of importance in the ordinary aqueous and related chemistry of iron are II and III. The oxidation states and stereochemistries are given in Table 17-E-l. 

The complexing tendencies decrease, on the whole, in the same order as the hydrolytic tendencies. The formation of complexes shifts the oxidation potentials, sometimes influencing the relative stabilities of oxidation states thus the formation of sulfate complexes of Np4+ and Np02+ is strong enough to cause disproportionation of Np02. 

Smith, D. W. Stability Index Diagrams Pictorial Representations of the Relative Stabilities of Oxidation States for Metallic Elements, J. Chem. Educ. 1996, 73, 1099-1102. 

Equation (3) can be used to calculate the standard electrode potentials. Calculations based on the Bom-Haber cycle to obtain the relative stabilities of oxidation states are known as Oxidation State Diagrams . These diagrams have been found useful in clarifying inorganic chemistry (69), even though their accuracy is sometimes low. 

Knowledge of the stable oxidation states of an element is very important since many other properties depend on these states. It is also important to know about the relative stability of oxidation states, i.e. redox potentials, for a chemical application. Trends in their values can also provide information about similarities or differences between the transactinides and their lighter homologues. Thus, for example, the stability of the maximum oxidation state is known to increase within transition element groups. It is therefore of great interest to investigate whether transactinides fall within this trend those at the beginning of the 6d row were expected to be stabilized in lower oxidation... 

It is difficult to discuss satisfactorily the relative stabilities of oxidation states (Table 19.3). The situation is complicated by the fact that low oxidation states for the heavier metals are stabilized in organometallic complexes, while in non-organometallic species, the stability of higher oxidation states tends to increase down a group. Consider group 6. 

Complexes. Iron(n) forms a number of complexes, most of them octahedral. Ferrous complexes can normally be oxidized to ferric complexes and the Fe Fe111 aqueous system provides a good example of the effect of complexing ligands on the relative stabilities of oxidation states ... 

One result of this work is the conclusion that in chromia-alumina, and in other supported oxides, there must be local concentration of the supported oxide. This conclusion is reached because the Weiss constant shows definite indication of exchange interaction at concentrations of the paramagnetic ion too low to cover the surface of the support with even a monolayer. Another conclusion is that the support is sometimes able to modify the relative stabilities of oxidation states in the supported oxide. For instance, manganese oxide supported on gamma-alumina tends to be stabilized in the tripositive state, while on high-area titania it reverts to the tetrapositive state. 

Liquid chemistry experiments. Relative stabilities of oxidation states, i.e. standard redox potentials E°, and influence of relativistic effects on them, can be established by reduction experiments. The E° can then be used to define heats of formation in the liquid phase by electrochemical methods through temperature variation of the standard reduction potential. 

The stability of oxidation states of the heaviest elements, and the influence of relativistic effects, can be investigated by reduction experiments. For that purpose, knowledge of relative stabilities of oxidation states, redox potentials E°, is of crucial importance E° is needed to decide which reducing or oxidizing agent should be chosen to reach the desired state. 

The pattern with the early transition metals—in the 3d series up to Mn, and for the 4d, 5d metals up to Ru and Os—is that the maximum oxidation state corresponds to the number of outer shell electrons. There is no trace of this behavior for lanthanides. The highest oxidation states of the 3d metals may depend upon complex formation (e.g., the stabilization of Co + by ammonia) or upon the pH (thus Mn04 (aq) is prone to disproportionation in acidic solution). Within the 3d series, there is considerable variation in relative stability of oxidation states, sometimes on moving from one metal to a neighbor thus, for iron, Fe + is more stable than Fe +, especially in alkaline conditions, while the reverse is true for cobalt. 

Knowledge of the relative stability of oxidation states of elements, i.e., redox potentials, E°, is very important for a chemical application. Trends in the stability of various oxidation states of the heaviest elements were predicted earlier on the... 

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