Iron complexes equilibrium constant

Iron, tris(hexafluoroacetylacetone)-structure, 65 Iron, tris(oxalato)-chemical actinometer, 409 Iron, tris(l,10-phenanthroline)-absorptiometry, 549 racemization, 466 solid state, 467 structure, 64 Iron(O) complexes magnetic properties, 274 Iron(II) complexes magnetic behavior, 273 spectra, 253 Iron(III) complexes equilibrium constant solvent effect, 516 liquid-liquid extraction, 539 magnetic behavior, 272 spectra, 253 Iron(IV) complexes magnetic behavior, 272 Isocyanates metal complexes hydrolysis, 429 Isokinetic effect ligand exchange solid state, 469 Isomerism, 179-208 configurational, 180, 188 constitutional, 180,182 coordination, 183 detection, 180 history, 24... 

This means that the sequestration equilibrium reaction will be pH-dependent. The constant K is known as the conditional equilibrium constant. However, for stability comparisons between complexes of the same denticity, it may be more convenient to compare the equilibrium constant for the proton independent reaction between iron and siderophore. This can also be useful in a theoretical sense, as it allows comparison of complex stability where siderophores have different protonation constants. However, this approach does not account for competition between H+ and Fe3+ for binding, which is always present in a real situation in aqueous solution. 

Stability comparisons between siderophore complexes with different binding stoichiometries are complicated by the fact that the units for the concentration equilibrium constants are different. Also, since the Fe3+ binding moieties have different pKa values competition for binding with H+ differs, which will not be reflected in the pH-independent / mlh values. Therefore, it is important to have a scale for iron-siderophore complex... 

It is necessary to consider a number of equilibrium reactions in an analysis of a hydrometallurgical process. These include complexing reactions that occur in solution as well as solubility reactions that define equilibria for the dissolution and precipitation of solid phases. As an example, in analyzing the precipitation of iron compounds from sulfuric acid leach solutions, McAndrew, et al. (11) consider up to 32 hydroxyl and sulfate complexing reactions and 13 precipitation reactions. Within a restricted pH range only a few of these equilibria are relevant and need to be considered. Nevertheless, equilibrium constants for the relevant reactions must be known. Furthermore, since most processes operate at elevated temperatures, it is essential that these parameters be known over a range of temperatures. The availability of this information is discussed below. 

Equilibrium constants for formation of iron(III) complexes of several oxoanions, of phosphorus, arsenic, sulfur, and selenium, have been reported. The kinetics and mechanism of complex formation in the iron(III)-phosphate system in the presence of a large excess of iron(III) involve the formation of a tetranuclear complex, proposed to be [Fc4(P04)(0H)2(H20)i6]. The high stability of iron(III)-phosphate complexes has prompted suggestions that iron-containing mixed hydroxide or hydroxy-carbonate formulations be tested for treatment of hyperphosphatemia. " ... 

Table III also shows the values of the equilibrium constants, KVAp for the conversion of iron nitrosyl complexes into the corresponding nitro derivatives. Keq decreases downwards, meaning that the conversions are obtained at a lower pH for the complexes at the top of the table. Thus, NP can be fully converted into the nitro complex only at pHs greater than 10. The NO+ N02 conversion, together with the release of N02 from the coordination sphere, are key features in some enzymatic reactions leading to oxidation of nitrogen hydrides to nitrite (14). The above conversion and release must occur under physiological conditions with the hydroxylaminoreductase enzyme (HAO), in which the substrate is seemingly oxidized through two electron paths involving HNO and NO+ as intermediates. Evidently, the mechanistic requirements are closely related to the structure of the heme sites in HAO (69). No direct evidence of bound nitrite intermediates has been reported, however, and this was also the case for the reductive nitrosylation processes associated with ferri-heme chemistry (Fig. 4) (25).

Mossbauer spectroscopy of the 57Fe nucleus has been extensively used to investigate aspects of spin equilibria in the solid state and in frozen solutions. A rigid medium is of course required in order to achieve the Mossbauer effect. The dynamics of spin equilibria can be investigated by the Mossbauer experiment because the lifetime of the excited state of the 57Fe nucleus which is involved in the emission and absorption of the y radiation is 1 x 10 7 second. This is just of the order of the lifetimes of the spin states of iron complexes involved in spin equilibria. Furthermore, the Mossbauer spectra of high-spin and low-spin complexes are characterized by different isomer shifts and quad-rupole coupling constants. Consequently, the Mossbauer spectrum can be used to classify the dynamic properties of a spin-equilibrium iron complex. 

The equilibrium constants K and f)2 increase as the ligand pKt increases. The increases in porphyrin basicity and solvent polarity also increase / 2, indicating the importance of the charge neutralization factor in the iron(III) porphyrin coordination chemistry (Table 6).86 For preparative purposes, five-coordinate complexes of the weak ligands are conveniently used to avoid contamination of the mixed ligand species Fe(Por)XL. 

Literally hundreds of complex equilibria like this can be combined to model what happens to metals in aqueous systems. Numerous speciation models exist for this application that include all of the necessary equilibrium constants. Several of these models include surface complexation reactions that take place at the particle-water interface. Unlike the partitioning of hydrophobic organic contaminants into organic carbon, metals actually form ionic and covalent bonds with surface ligands such as sulfhydryl groups on metal sulfides and oxide groups on the hydrous oxides of manganese and iron. Metals also can be biotransformed to more toxic species (e.g., conversion of elemental mercury to methyl-mercury by anaerobic bacteria), less toxic species (oxidation of tributyl tin to elemental tin), or temporarily immobilized (e.g., via microbial reduction of sulfate to sulfide, which then precipitates as an insoluble metal sulfide mineral). 

If the reaction between iron(III) and thiocyanate ions yielded an equilibrium concentration of 0.2 M for each of these ions, what would be the equilibrium concentration of the red iron-thiocyanate complex Hint The equilibrium constant can be found in the Background section. 

Conditional (apparent) equilibrium constants - Equilibrium constants that are determined for experimental conditions that deviate from the standard conditions used by convention in - thermodynamics. Frequently, the conditional equilibrium conditions refer to - concentrations, and not to - activities, and in many cases they also refer to overall concentrations of certain species. Thus, the formal potential, i.e., the conditional equilibrium constant of an electrochemical equilibrium, of iron(II)/iron(III) may refer to the ratio of the overall concentrations of the two redox forms. In the case of complex equilibria, the conditional - stability constant of a metal ion Mm+ with a ligand L" refers to the overall concentration of all complex species of Mm+ other than Conditional equilibrium... 

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