Oxidation states dependencies

Oxidation can also occur at the central metal atom of the phthalocyanine system (2). Mn phthalocyanine, for example, can be produced ia these different oxidation states, depending on the solvent (2,31,32). The carbon atom of the ring system and the central metal atom can be reduced (33), some reversibly, eg, ia vattiag (34—41). Phthalocyanine compounds exhibit favorable catalytic properties which makes them interesting for appHcations ia dehydrogenation, oxidation, electrocatalysis, gas-phase reactions, and fuel cells (qv) (1,2,42—49). 

The redox potential and the reactivity of this oxidation state depend strongly upon the anion (Table 11). Strong complexes are formed with SO ". Even in perchloric acid, hydrolysis and polymerisation greatly complicate kinetics. The co-ordination number of Ce(lV) in solution is not established . 

Figure 3.8 shows a variety of materials. This, of course, is not surprising. In principle, the composition of a solid material will depend on several factors, including the reaction conditions. For example, when an oxidation is carried out a metal like Co will be in the metallic state or the oxidized. state depending on the reaction conditions. When used in chlorination many systems will be present as chlorides. 

The complex Ni[(S2C2(CF3)2)]2 (392) is able to bind light olefins selectively and reversibly.1081 According to Scheme 4, the reaction of olefins with (392) can be controlled electrochemically, where the oxidation state-dependent binding and release of olefins is fast on the electrochemical timescale. Olefin binding is supposed to occur via the ligand S-donors. 

In addition, the determination of metal-ligand bond distances in solution and their oxidation state dependence is critical to the application of electron transfer theories since such changes can contribute significantly to the energy of activation through the so-called inner-sphere reorganizational energy term. 

A. L. Terthienyl and Poly-terthienyl Ligands as Redox-Switchable Hemilabile Ligands for Oxidation-State-Dependent Molecular Uptake and Release. J. Am. Chem. Soc. 2001, 123, 2503-2516. 

Scheme 9.14 Oxidation state-dependent stereoselectivity in a-insertions into a Rh vinylidene.

Most transition-metal cations can adopt several different oxidation states depending on the method of preparation and the compound in which they find themselves, but which oxidation state they adopt in a particular compound is not always clear from the chemical formula or from the nature of the bonding environment. Providing that the oxidation state is not zero, the bond valence model can help because the metal ligand bond can usually be described as an... 

Furukawa Y, Ishimori K, Morishima I. Oxidation-state-dependent protein docking between cytochrome c and cytochrome bs high-pressure laser flash photolysis study. Biochemistry 2002 41 9824-32. 

Uranium can be dissolved in dilute acids, when uranium(IV) ions, U4+, and hydrogen gas are formed. Uranium(IV) ions can easily be oxidized to the hexavalent state, which is the most stable oxidation state of uranium. At this oxidation state, depending on the pH of the solution, two ions can be formed the uranyl cation, UO +, is stable in acid solutions, while the diuranate anion, u2or, in alkaline media. The two ions are in equilibrium with each other ... 

Iron and manganese can have different oxidation states, depending on the redox conditions of the environment. Iron(II) compounds, however, are only stable under anaerobic conditions they transform iron(III) compounds on the effect of air and groundwaters (pH = 6-8), therefore, the interfacial processes of iron(II) oxides and hydroxide can play a smaller role under environmental conditions. (Note The iron(II) of silicates can also transform into iron(III) during weathering.)... 

Crabtree and coworkers found a similar oxidation state dependent coordination behaviour for related iridium(I) and iridium(III) bis-carbene complexes [336]. 

Complexes containing vanadium in low oxidation states, apart from organometallic compounds, are known with ligands such as bipy, phen, nitric oxide, and tertiary phosphines, which stabihze such oxidation states. Depending on their electronic structure, V and V complexes may be diamagnetic, which permits study by NMR spectroscopy, and EPR spectroscopy has been used to study paramagnetic V complexes. 

Some accounts on the redox-induced switching of hyperpolarisabilities utilised penta-ammine ruthenium complexes bearing substituted 4,4 -bipyri-dinium coligands. The intense bipyridinium Ru LMCT band at 580 to 636 nm bleaches upon reduction of the metal centre, thus switching off their quadratic NLO response. The oxidation of the ferrocene donor in an ethenyl-linked ferrocene-nitrothiophene dyad likewise results in a decrease of the quadratic NLO response by about one order in magnitude. Oxidation-state-dependent quadratic NLO performance has also been noted by Lapinte and coworkers who compared the complexes Cp (dppe)Fe—C=CPh, Cp (dppe)Fe-C=C- 2(p-C6H4-l,4), Cp (dppe)Fe-C=C- 2(g-C6H4-l,3),... 

By far the most common oxidation state among the lanthanides is + 3, although some + 2 ions have also been found. - For all the + 3 cations of the lanthanides, the electron configuration is identical, namely, 4f 5d 6s . First-row transition-metal ions, on the other hand, have variable oxidation states, dependent on their propensity to attain stable, orbital configurations, ranging from + 1 to +7 oxidation states. 

---