Oxidation state definition

Five oxidation states of At have been definitely established (-1, 0, +1, V, VII) and one other (III) has been postulated. The standard oxidation potentials connecting these states in 0.1 M acid solution are E°fV) ... 

Other ions which are reduced in the reductor to a definite lower oxidation state are those of titanium to Ti3+, chromium to Cr2+, molybdenum to Mo3+, niobium to Nb3+, and vanadium to V2 +. Uranium is reduced to a mixture of U3 + and U4+, but by bubbling a stream of air through the solution in the filter flask for a few minutes, the dirty dark-green colour changes to the bright apple-green colour characteristic of pure uranium(I V) salts. Tungsten is reduced, but not to any definite lower oxidation state. 

Earlier in this chapter, we learned definitions for the terms oxidation and reduction. We saw that oxidation involves an increase in oxidation state. For example, oxidation of a secondary alcohol will produce a ketone ... 

As a result of strong electronic interactions between the two metalloporphyrin units, there is a substantial uncertainty in assigning oxidation states in mixed-valence group 2 complexes of redox-active metals, such as Co. Thus, although reduced neutral C02 derivatives can be reasonably well described as those of Co the location (metal versus porphyrin) of the electron hole(s) in the singly and doubly oxidized derivatives is not known definitively, and may be very sensitive to the medium [LeMest et al., 1996, 1997]. For example, in benzonitrile, the UV-vis spectmm of [(FTF4)Co2]" ... 

The concept of the oxidation state of an element in a chemical compound has a long and confusing history. In the most pretentious form of the concept the oxidation state or oxidation number is the electrical charge localised on the concerned atom in the compound. Confusion arises when we realise that the definition of the atomic domain is arbitrary and the experimental determination of the electrical charge in the once chosen domain is often problematic. 

According to Nyholm and Tobe (i) The definition of a usual oxidation state refers to oxidation states that are stable in environments made up of those chemical species that were common in classical inorganic compounds, e.g. oxides, water and other simple... 

The concepts of formal oxidation state, spectroscopic oxidation state, oxidation number are often subject to controversial discussion. Regarding the definitions, the reader is referred to Appendix F and [22, 23]. 

Proton electroreduction catalyzed by metal complexes is different from reduction at a metal electrode. It definitely involves the formation of metal hydride species through protonation of electroreduced, low-oxidation-state metal complexes that function as Bronsted base (Equation (5)). From protonated... 

The mentioned method for synthesis of oxide-hydroxide compounds (Ni, Cr, Co) is more controllable and enables with production of electrode films definite amounts of components. Therefore it guarantees the reproducibility of their compositions and properties. Using the above method we were able to produce the following oxide compounds zero valence metal and lowest oxidation state oxide-hydroxide compounds in cathode process and oxide-hydroxide compounds (in anode process the oxide compounds consist of highest oxidation state oxide-hydroxide compounds). Both type compounds possesses electronic and ionic conductivity. 

The report of the first zinc compound with a Zn-Zn core elicited a number of critical comments on the structure and bonding of decamethyldizincocene, and the interpretation of the results.236,237 None of the authors of these commentaries questioned the data or their interpretation. Parkin, however, has pointed out that the formal oxidation state of +1 for zinc in this compound is merely due to the convention that metals are assigned an oxidation state of 0 when they form bonds with like atoms.237 If the conventional definition of valence, namely the capacity of atoms to form bonds to other atoms is used, then the zinc atoms in decamethyldizincocene are not monovalent, but divalent. The synthesis of a paramagnetic organozinc compound in which zinc uses only one of its two 4s electrons will remain an interesting challenge to many synthetic organometallic chemists. 

The model shown in Scheme 2 indicates that a change in the formal oxidation state of the metal is not necessarily required during the catalytic reaction. This raises a fundamental question. Does the metal ion have to possess specific redox properties in order to be an efficient catalyst A definite answer to this question cannot be given. Nevertheless, catalytic autoxidation reactions have been reported almost exclusively with metal ions which are susceptible to redox reactions under ambient conditions. This is a strong indication that intramolecular electron transfer occurs within the MS"+ and/or MS-O2 precursor complexes. Partial oxidation or reduction of the metal center obviously alters the electronic structure of the substrate and/or dioxygen. In a few cases, direct spectroscopic or other evidence was reported to prove such an internal charge transfer process. This electronic distortion is most likely necessary to activate the substrate and/or dioxygen before the actual electron transfer takes place. For a few systems where deviations from this pattern were found, the presence of trace amounts of catalytically active impurities are suspected to be the cause. In other words, the catalytic effect is due to the impurity and not to the bulk metal ion in these cases. 

By definition, an oxidative carbonylation is a process in which carbon monoxide is inserted into an organic substrate under the action of a metal undergoing a reduction of its oxidation state [the reduction Pd(II) -> Pd(0)... 

Comments on some trends and on the Divides in the Periodic Table. It is clear that, on the basis also of the atomic structure of the different elements, the subdivision of the Periodic Table in blocks and the consideration of its groups and periods are fundamental reference tools in the description and classification of the properties and behaviour of the elements and in the definition of typical trends in such characteristics. Well-known chemical examples are the valence-electron numbers, the oxidation states, the general reactivity, etc. As far as the intermetallic reactivity is concerned, these aspects will be examined in detail in the various paragraphs of Chapter 5 where, for the different groups of metals, the alloying behaviour, its trend and periodicity will be discussed. A few more particular trends and classification criteria, which are especially relevant in specific positions of the Periodic Table, will be summarized here. 

In the years since the discovery of nickel and iron in the catalytic centres, numerous different descriptions of the catalytic cycle of hydrogenase have been proposed. These were based on different oxidation states of the metal centres, and different sequences of transfer of electrons and hydrous. Although the reaction cycle has not been definitively resolved, the spectroscopic evidence places constraints on possible models that should be considered. 

Kockerling, M. and Henkel, G. (1993) Mononuclear nickel thiolate complexes containing nickel sites in different oxidation states - molecular definition of [Ni(SCgH40)2] and [Ni(SCgH40)2]-, Chem. Ber., 126, 951-3. 

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