Subject oxidation states

Like mthenium, amines coordinated to osmium in higher oxidation states such as Os(IV) ate readily deprotonated, as in [Os(en) (NHCH2CH2NH2)] [111614-75-6], This complex is subject to oxidative dehydrogenation to form an imine complex (105). An unusual Os(IV) hydride, [OsH2(en)2] [57345-94-5] has been isolated and characterized. The complexes of aromatic heterocycHc amines such as pyridine, bipytidine, phenanthroline, and terpyridine ate similar to those of mthenium. Examples include [Os(bipy )3 [23648-06-8], [Os(bipy)2acac] [47691-08-7],... 

Chromium Exposure Levels and U.S. Government Regulations. The level of exposure to chromium compounds for employees in industry and for the general population via waste disposal and industrial emissions is the subject of much regulation, research, and controversy. Some U.S. Government regulations, such as the Comprehensive Environmental Response, Compensation, and LiabiUty Act (CERCLA), also known as the Superfund Act, make no distinction as to the oxidation state of chromium (144). However, there is valence distinction in other regulations. 

Lower oxidation states are rather sparsely represented for Zr and Hf. Even for Ti they are readily oxidized to +4 but they are undoubtedly well defined and, whatever arguments may be advanced against applying the description to Sc, there is no doubt that Ti is a transition metal . In aqueous solution Ti can be prepared by reduction of Ti, either with Zn and dilute acid or electrolytically, and it exists in dilute acids as the violet, octahedral [Ti(H20)6] + ion (p. 970). Although this is subject to a certain amount of hydrolysis, normal salts such as halides and sulfates can be separated. Zr and are known mainly as the trihalides or their derivatives and have no aqueous chemistry since they reduce water. Table 21.2 (p. 960) gives the oxidation states and stereochemistries found in the complexes of Ti, Zr and Hf along with illustrative examples. (See also pp. 1281-2.)... 

The mechanism by which this low oxidation state is stabilized for this triad has been the subject of some debate. That it is not straightforward is clear from the fact that, in contrast to nickel, palladium and platinum require the presence of phosphines for the formation of stable carbonyls. For most transition metals the TT-acceptor properties of the ligand are thought to be of considerable importance and there is... 

In a different set of experiments solutions of Pu(III) or Pu(VI) in H2O (Ar saturated, pH adjusted to 7, 2 x 10-5 M in Pu) were irradiated in the ANL 60Co-y source at a position where the dose was 1 megarad/hr (Jj) 1 mM H2O2 produced/hr. Cation exchange column behavior was used in an attempt to identify Pu oxidation states, see Table III. The results obtained after an irradiation of 1 hr. were indistinguishable from the "blank", i.e. a solution not subjected to irradiation. The irradiation for a 24 hr. period failed to demonstrate a marked increase in the amount of Pu(IV) produced that could be ascribed to the effects of radiolysis. 

When a solution of Pu(VI) is subjected to the 24 hr. irradiation the bulk of the Pu has been reduced to the Pu(III) oxidation state. There exists the ambiguity that residence on the column may cause some reduction of Pu(VI) Pu(V) and... 

One problem that should be of particular interest for separation processes is the identification and kinetic characterization of the reactive radicals that occur when strong nitric acid solutions are subject to ionizing radiation. The important reducing radical in such solutions is the H atom. There are presently no direct measurements of the rate of reduction of H atoms with any Pu oxidation state. 

The possible application of aqueous plutonium photochemistry to nuclear fuel reprocessing probably has been the best-received justification for investigating this subject. The necessary controls of and changes in Pu oxidation states could possibly be improved by plutonium photochemical reactions that were comparable to the uranyl photochemistry. 

The sulfur-rich oxides S 0 and S 02 belong to the group of so-called lower oxides of sulfur named after the low oxidation state of the sulfur atom(s) compared to the best known oxide SO2 in which the sulfur is in the oxidation state +4. Sulfur monoxide SO is also a member of this class but is not subject of this review. The blue-green material of composition S2O3 described in the older literature has long been shown to be a mixture of salts with the cations S4 and Ss and polysulfate anions rather than a sulfur oxide [1,2]. Reliable reviews on the complex chemistry of the lower sulfur oxides have been published before [1, 3-6]. The present review deals with those sulfur oxides which contain at least one sulfur-sulfur bond and not more than two oxygen atoms. These species are important intermediates in a number of redox reactions of elemental sulfur and other sulfur compounds. 

The reaction between Co(III) and Ce(III) has been the subject of a detailed study in a series of papers by Sutcliffe and Weber . Of particular value is the thorough investigation of the influence of anions on the rate in perchlorate media. The reaction was followed by measuring the disappearance of Co(IIl) at its absorption maximum of 650 m/i, a wavelength where both oxidation states of cerium are transparent and Co(II) absorbs only slightly. Changes in temperature and ionic strength affect the spectrum of Ce(III) at the 296 m/i maximum, but the... 

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]. 

Earlier studies demonstrated a rich variety of oxidation states, geometries and compositions of the intermediates and products formed in the autoxidation reactions of cysteine (RSH). Owing to the complexity of these systems, only a limited number of detailed kinetic papers were published on this subject and, not surprisingly, some of the results are... 

It would be hardly possible to do full justice to the kinetic behavior of cobalt even in a book devoted to that subject. Only some important features will be emphasized. The stable oxidation states in aqueous solution are Co(II) and Co(III). 

Selenium has a complex chemistry in the environment because of its multiple oxidation states and variable surface adsorption properties. Qualitatively it is analogous to sulfur occurring in the oxidation states +6 (selenate, Se04 ), +4 (selenite, SeOs "), 0 (elemental selenium) and —2 (Se, selenide) The Se anion closely resembles S (radii 0.20 and 0.185nm, respectively) and is often associated with sulfide minerals. Also, like S, Se is subject to volatilization through biological methylation. 

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