Oxidation states oxide complexes

The Table shows a great spread in Kd-values even at the same location. This is due to the fact that the environmental conditions influence the partition of plutonium species between different valency states and complexes. For the different actinides, it is found that the Kd-values under otherwise identical conditions (e.g. for the uptake of plutonium on geologic materials or in organisms) decrease in the order Pu>Am>U>Np (15). Because neptunium is usually pentavalent, uranium hexavalent and americium trivalent, while plutonium in natural systems is mainly tetravalent, it is clear from the actinide homologue properties that the oxidation state of plutonium will affect the observed Kd-value. The oxidation state of plutonium depends on the redox potential (Eh-value) of the ground water and its content of oxidants or reductants. It is also found that natural ligands like C032- and fulvic acids, which complex plutonium (see next section), also influence the Kd-value. 

Similar effects are observed in the iron complexes of Eqs. (9.13) and (9.14). The charge on the negatively charged ligands dominates the redox potential, and we observe stabilization of the iron(iii) state. The complexes are high-spin in both the oxidation states. The importance of the low-spin configuration (as in our discussion of the cobalt complexes) is seen with the complex ions [Fe(CN)6] and [Fe(CN)6] (Fq. 9.15), both of which are low-spin. 

The reaction between Fe(IlI) and Sn(Il) in dilute perchloric acid in the presence of chloride ions is first-order in Fe(lll) concentration . The order is maintained when bromide or iodide is present. The kinetic data seem to point to a fourth-order dependence on chloride ion. A minimum of three Cl ions in the activated complex seems necessary for the reaction to proceed at a measurable rate. Bromide and iodide show third-order dependences. The reaction is retarded by Sn(II) (first-order dependence) due to removal of halide ions from solution by complex formation. Estimates are given for the formation constants of the monochloro and monobromo Sn(II) complexes. In terms of catalytic power 1 > Br > Cl and this is also the order of decreasing ease of oxidation of the halide ion by Fe(IlI). However, the state of complexing of Sn(ll)and Fe(III)is given by Cl > Br > I". Apparently, electrostatic effects are not effective in deciding the rate. For the case of chloride ions, the chief activated complex is likely to have the composition (FeSnC ). The kinetic data cannot resolve the way in which the Cl ions are distributed between Fe(IlI) and Sn(ll). 

Halide addition to a cationic carbyne complex, [L M=CR]+, or halogen oxidation of a low oxidation state carbyne complex are both potential routes to monohalocarbene species. Examples of the first process are well known for carbyne complexes from Groups 6 and 7 of the periodic table (120), e.g.,... 

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... 

In the Cp2M(dithiolene) series, d° complexes were investigated essentially with Ti, and to a lesser extent with Zr and Hf, in their IV oxidation state. These complexes can be reversibly reduced to the d1, Tim anionic species but they were never isolated in the solid state. Attempts to oxidize these d° complexes were also unsuccessful, as electrochemical oxidation leads to their decomposition [23, 24]. The essential structural characteristic of these d° complexes is the strong folding of... 

In the determination of cadmium in seawater, for both operational reasons and ease of interpretation of the results it is necessary to separate particulate material from the sample immediately after collection. The dissolved trace metal remaining will usually exist in a variety of states of complexation and possibly also of oxidation. These may respond differently in the method, except where direct analysis is possible with a technique using high-energy excitation, such that there is no discrimination between different states of the metal. The only technique of this type with sufficiently low detection limits is carbon furnace atomic absorption spectrometry, which is subject to interference effects from the large and varying content of dissolved salts. 

High oxidation state alkylidene complexes in which a heteroatom is bound to the alkylidene carbon atom are extremely rare [41]. Since the approach shown in Eq. 43 failed, the related approach shown in Eq. 44 was taken to prepare the medium-sized ring subunits [222]. The latter product was formed in good yield when n=2, R H, R2=Et, but only poor yield when n=2, R =Et, R2=H, possibly due to unfavorable interactions between the ethyl substituent and transannular groups in the transition state for cyclization of the allyl ether [222]. Ruthenium catalysts either failed or gave low yields, presumably because of the steric hindrance associated with ring-closing dienes of this type. 

Europium and ytterbium di-valence. The oxidation state II for Eu and Yb has already been considered when discussing the properties of a number of divalent metals (Ca, Sr, Ba in 5.4). This topic was put forward again here in order to give a more complete presentation of the lanthanide properties. The sum of the first three ionization enthalpies is relatively small the lanthanide metals are highly electropositive elements. They generally and easily form in solid oxides, complexes, etc., Ln+3 ions. Different ions may be formed by a few lanthanides such as Ce+4, Sm+2, Eu+2, Yb+2. According to Cotton and Wilkinson (1988) the existence of different oxidation states should be interpreted by considering the ionization... 

Upon passing from the Ni(II) to the Ni(IV) oxidation states, the complex maintains the octahedral geometry, but important Ni-N bond shortenings occur (by about 0.1 A in the equatorial plane and by about 0.15 A in the axial positions). 

Fig. 24. Plot of out-of-plane shifts vs. oxidation state for complexes [(( ArO)3tacn)U(Lax)].

Fig. 8-33. Energy diagram showing a shift of redox electron level due to complexation of reductant and oxidant particles (1) afSnity for complexation is greater with oxidants than with reductants, (2) affinity for complexation is greater with reductants than with oxidants. COMPLEX z ligand-coordinated complex redox particles HYDRATE = simply hydrated redox particles W = probability density of electron states e., ) - standard Fermi level of hydrated redox particles - standard Fermi level of ligand-coordinated...

As a general guideline it can be stated that a-deprotonation of transition metal alkyl complexes will be easy when the metal is in a high oxidation state, the complex is positively charged, and the additional ligands are poor 7t-donors. 

Rogers MM, Stahl SS (2006) N-Heterocyclic Carbenes as Ligands for High-Oxidation-State Metal Complexes and Oxidation Catalysis. 21 21-46 Roland S, Mangeney P (2005) Chiral Diaminocarbene Complexes, Synthesis and Application in Asymmetric Catalysis. 15 191-229 Roll R, see Behr A (2008) 23 19-52... 

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