Higher-Valency Metal Ions

Ligand Substitution on Higher-Valency Metal Ions 

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Other semiconductor monomers are formed from A provided by a soluble salt and M resulting from the radiolytic reduction (for instance by e ) of a higher valency metal ion ... 

The opposite situation, a metal-excess or -type scale, is also possible (zinc is an example). In this case, extra metal ions are believed to occupy intermediate positions in the scale. The introduction of a higher valence metal ion will reduce the number of zinc ions in the scale and thereby lower the oxidation rate. A lower valence metal ion will, of course, have the opposite effect, causing the metal-excess scale to respond to the addition of other metal ions in a manner just the reverse of that in metal-deficit scales. 

Oxidation of variable valence metal ions to higher valence state is desirable, for example, in hydrometallurgy, water conditioning, etc. The kinetics of Fe(II) and Ti(III) oxidation by oxygen in acidified water solutions was investigated. An investigation of oxidation process kinetics was carried out in the same equipment as mentioned above. It was established that... 

Moreover, the structure destruction of EAH-USY by metals was found to be related to the valence state of the metal ions. As shown in Figure 8, the higher the valence of metal ions, the more serious the structural effect of these metals. This might be explained either by the repulsive force between metal ions or the difficulty of diffusion of low valence metal ions in zeolite inner chaimels due to their large radius. In commercial RFCC units, it is useful to alleviate metal contamination by controlling the excess oxygen concentration in regenerator in order to keep the metals deposited on catalysts in a low valence state. 

In contrast with their oxide counterparts, CaFj and PbFj can form fluorite-type solid solutions with fluorides of higher-valency metals such as YFj, BiFj, UF4, etc. They are expressed, for example, by Cai xYxF2+x, in which the excess F" ions are accommodated in the interstitial sites, forming various kinds of clusters with Vp, depending on the concentration of F . They are usually good F solid electrolytes, and the conductivity of Pbj.xBixFj+x (x = 0.25) is shown in Figure 6.3 as an example. 

As stated previously, the curing of thiol-terminated liquid polysulfide polymers involves the oxidation of the mercaptan to disulfide using higher valency metal oxides or p-quinonedioxime. Consequently, the cured polymers will contain reduced forms of the metal ions or p-phenylenediamine heterogeneously dispersed in them. 

Higher valence-state metal ions can abstract hydrogen from a hydroperoxide (25) (eq. 35) or from a substrate (eq. 36). 

The diffusion of metal ions in vitreous siUca has not been studied as extensively as that of the gaseous species. The alkaU metals have received the most attention because their behavior is important in electrical appHcations. The diffusion coefficients for various metal ions are Hsted in Table 5. The general trend is for the diffusion coefficient to increase with larger ionic sizes and higher valences. 

Electrolysis. Electrowinning of zirconium has long been considered as an alternative to the KroU process, and at one time zirconium was produced electrolyticaHy in a prototype production cell (70). Electrolysis of an aH-chloride molten-salt system is inefficient because of the stabiUty of lower chlorides in these melts. The presence of fluoride salts in the melt increases the stabiUty of in solution, decreasing the concentration of lower valence zirconium ions, and results in much higher current efficiencies. The chloride—electrolyte systems and electrolysis approaches are reviewed in References 71 and 72. The recovery of zirconium metal by electrolysis of aqueous solutions in not thermodynamically feasible, although efforts in this direction persist. 

Rates of Reaction. The rates of formation and dissociation of displacement reactions are important in the practical appHcations of chelation. Complexation of many metal ions, particulady the divalent ones, is almost instantaneous, but reaction rates of many higher valence ions are slow enough to measure by ordinary kinetic techniques. Rates with some ions, notably Cr(III) and Co (III), maybe very slow. Systems that equiUbrate rapidly are termed kinetically labile, and those that are slow are called kinetically inert. Inertness may give the appearance of stabiUty, but a complex that is apparentiy stable because of kinetic inertness maybe unstable in the thermodynamic equihbrium sense. 

The two elements have similar electronegativity. (Note electronegativity is the power of an element to attract electrons to itself when present in a molecule or in an aggregate of unlike atoms it is a different property from the electrode potential, which depends on the free energy difference between an element in its standard state and a compound or ion in solution (see Section 20.1).) In addition a metal of a lower valency tends to dissolve a metal of a higher valency more readily than vice versa. 

Peroxyl radicals with a strong oxidative effect along with ROOH are continuously generated in oxidized organic compounds. They rapidly react with ion-reducing agents such as transition metal cations. Hydroxyl radicals react with transition metal ions in an aqueous solution extremely rapidly. Alkyl radicals are oxidized by transition metal ions in the higher valence state. The rate constants of these reactions are collected in Table 10.5. 

Most metal oxides are ionic crystals and belong to either the class of semiconductors or insulators, in which the valence band mainly comprises the frontier orbitals of oxide ions and the conduction band contains the frontier orbitals of metal ions. In forming an ionic metal oxide ciTstal from metal ions and oxide ions, as shown in Fig. 2-21, the crystalline field shifts the frontier electron level of metal ions to higher energies to form an antibonding band (the conduction... 

The oxides of low-valency metals (i.e., with cations in oxidation number < -i-4) are typically ionic compounds [76]. They are most frequently easily obtained in crystalline forms. In ionic metal oxides the coordination of the cations (four to eight) is generally higher than their valency (one to four) and this also occurs for the coordination of 0 oxide ions (three to six). The bulk basic nature of the ionic metal oxides is associated with the strong polarization of the metal-oxygen bond, to its tendency to be dissociated by water and to the basic nature of the products of their reaction with water (i.e., the metal hydroxides) [67]. 

In aqueous solutions, metal ions in their higher oxidation states oxidize H2S, forming a lower-valence sulfide and sulfur ... 

It will be noted that with the exception of the organic cations and anions the more mobile hydrogen and hydroxyl ions are most readily adsorbed, whilst in the case of the metallic ions the influence primarily of the valency of the ion and both the position of the metal in the eleotrolytic potential series as well as the ionic mobility is most marked, the higher the valency and the more noble the element the more readily it is adsorbed. 

In the liquid-phase oxidation of acrolein, the metal ion with higher valence coordinates acrolein to produce an acyl radical by hydrogen abstraction. 

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