Oxidation state of transition metals

The performance of many metal-ion catalysts can be enhanced by doping with cesium compounds. This is a result both of the low ionization potential of cesium and its abiUty to stabilize high oxidation states of transition-metal oxo anions (50). Catalyst doping is one of the principal commercial uses of cesium. Cesium is a more powerflil oxidant than potassium, which it can replace. The amount of replacement is often a matter of economic benefit. Cesium-doped catalysts are used for the production of styrene monomer from ethyl benzene at metal oxide contacts or from toluene and methanol as Cs-exchanged zeofltes ethylene oxide ammonoxidation, acrolein (methacrolein) acryflc acid (methacrylic acid) methyl methacrylate monomer methanol phthahc anhydride anthraquinone various olefins chlorinations in low pressure ammonia synthesis and in the conversion of SO2 to SO in sulfuric acid production. 

ELECTRONIC CONFIGURATIONS AND OXIDATION STATES OF TRANSITION METALS... 

Inorganic and physical chemistry Electronic configurations and oxidation states of transition metals... 

Among electrode processes with at least one charge transfer step, several different types of reaction can be found. The simplest interfacial electrochemical reactions are the exchange of electrons across the electrochemical interface by flipping oxidation states of transition metal ions in the electrolyte adjacent to the electrode surface. The electrode in this case is merely the source or sink of electrons, uptaking electrons from the reduced species and releasing them to the oxidized redox species in solution. Examples of simple electron transfer reactions are... 

If most of the research on crown and cage thioethers has concerned their synthesis and exploratory work on their coordination chemistry, their complexing properties and capacity to stabilize low oxidation states of transition metals should be expected to lead to new applications, as for their oxygen and nitrogen analogues. 

D. Formal Oxidation States of Transition Metal Atoms. 71... 

Being paramagnetic 0 can be detected by EPR at low temperatures (20.22). At the same time 0 states are potent oxidation agents they interact with transition metal cations in low oxidation states causing their oxidation/ e.g. Fe2+ + 0 = Fe3+ + 02 . Thus/ one way to follow the peroxy dissociation is to study the concomitant changes in the oxidation states of transition metal impurities by EPR (23.). At the surface the chemical expression of 0" states is one of peroxide and/or superoxide functionality. A superoxide may be viewed as an 0 trimer or as 0 trapped by a surface peroxy ... 

In the previous chapter it was shown how measurements of polarized absorption spectra in the visible to near-infrared region can provide information on such crystal chemical problems as oxidation states of transition metal ions, coordination site symmetries and distortions, cation ordering and the origins of colour and pleochroism of minerals. Much attention was focused in chapter 4 on energies of intervalence charge transfer transitions appearing in electronic absorption spectra of mixed-valence minerals. 

As it was demonstrated by staining the oxidized polypropylene and its observation by UV microscope, a high degree of inhomogeneity at the micron level was observed even for the most thoroughly annealed samples. In most cases this is clearly associated with the catalyst residues. An observation of microdomains in the oxidized polymer in which the degree of oxidation is by far pronounced than in the rest of polymer may be explained by the effect of higher oxidation state of transition metal ions M which interact directly with polymer ... 

Equilibria involving reductive dissolution reactions add to the complexity of mineral solubility phenomena in just the way that pE-pH diagrams are more complicated than ordinary predominance diagrams, like that in Fig. 3.7. The electron activity or pE value becomes one of the master variables whose influence on dissolution reactions must be evaluated in tandem with other intensive master variables, like pH or p(H4Si04). Moreover, the status of microbial catalysis under the suboxic conditions that facilitate changes in the oxidation states of transition metals has to be considered in formulating a thermodynamic description of reductive dissolution. This consideration is connected closely to the existence of labile organic matter and, in some cases, to the availability of photons.26... 

The determination of oxidation states of transition metals such as vanadium, chromium, or molybdenum in supported oxides is difficult, because many of the reduced phases are weak Raman scatterers. In such cases, the combination of UV—vis DRS and Raman spectroscopy is essential for identifying the reduced oxidation states and the extent of reduction. UV—vis DRS provides information about the changes in oxidation state (Weckhuysen, 2003) and the extent of reduction (Gao et al., 1999), and it permits determination of the specific wavelengths at which it is possible to resonantly enhance the Raman signal. 

A considerable collection of data exists that describe the state of catalysts under reaction conditions. The cases presented here show that typical processes observed under reaction conditions include changes of the oxidation states (of transition metals), changes of particle size and shape (of metal clusters), or formation of coke. However, without the corresponding catalytic performance, relevant and spectator species cannot be distinguished. 

Explain why high oxidation states of transition metals are stabilized by complexing the metal ions with NH3, whereas low oxidation states are stabilized by complexing with CO. 

Although normally PF3 stabilizes low oxidation states of transition metals it has been possible in some cases to directly oxidize a low-valent complex with chlorine (method F). 

Ans. (a) Co + and Co + (the oxidation states of transition metals very in steps of one.) (b) TP and T1+ (the maximum oxidation state of a group III element and the state 2 less than the maximum.) (c) Sn" + and Sn + (the maximum oxidation state of a group IV element and the state 2 less than the maximum.) (d) Cu+ and Cu + (the maximum oxidation state for the coinage metals is greater than the group number.)... 

The oxidation state of transition metals can be controlled by using appropriate oxidants or reductants see Formal Oxidation State and Oxidation Number). 

It is alloyed with about 4% A1 and 0.02% Mg. The aluminum strengthens the zinc and also prevents the molten alloy from attacking the steel pressure casting dies. Zinc readily reacts with mercury or will displace mercury from a mercury(II) salt to form an amalgam that is usefril for reductions, as in the preparation of compounds of the lower oxidation states of transition metals and lanthanides (e.g. Cr , V , Eu°, dimeric Mo ) and in analytical chemistry (e.g. in the Jones reductor see Analytical Chemistry of the Transition Elements). 

Chemistry of the Various Oxidation States of Transition Metals 580 The Chemistry of Elements Potassium-Zinc Comparison by Electron Configuration 582... 

Chemistry o( the Various Oxidation States of Transition Metals... 

The NASICON structure was chosen because it can be readily synthesized, is thermally very stable, and can accommodate a large fraction of vacancies and cation substitutions [9-12], In addition, this structure possesses two features which should be important for the catalyst design as envisioned above. First, it is a phosphate and hence expected, owing to its acidic nature, to stabilize the lower oxidation states of transition metals, e.g., V second, owing to its structure, layered octahedral metal centers with variable valence are separated from each other by redox inactive tetrahedral phosphate groups, i.e., the structure provides for isolation of descrete layers. 

Oxides are the most common materials in our environment because of the oxygen partial pressure in air and pressurized oxygen has been developed as a reactive medium to prepare new phases containing unusual oxidation states of transition metals. Figure 7.10 shows a three-stage compression equipment built in Bordeaux to develop high oxygen pressures (up to 500 MPa at room temperature). ... 

This chapter illustrates the complementarity of photochemical and radiation chemical techniques to elucidate elementary pathways in mechanistically rich systems. Some of the mechanistic conclusions that have resulted from these studies in aqueous media are presented. Extreme (both high and low) oxidation states of transition-metal complexes are included. Reactivity with respect to electron transfer reactions and small-molecule activation are addressed. 

Novel rathenium complexes with carborane ligands were employed as efficient catalysts for controlled polymer synthesis via Atom Transfer Radical Polymerization (ATRP) mechanism. The ability of carborane ligands to stabihze high oxidation states of transition metals allows the proposed catalysts to be more active than their cyclopentadienyl counterparts. The proposed catalysts do not reqnire additives such as aluminium alkoxides. It was shown that introdnction of amine additives into the polymerization mixture leads to a dramatic increase of polymerization rate leaving polymerization controlled. The living nature of polymerization was proved via post-polymerization and synthesis of block copolymers. 

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