Iron hydroxide complexes, formation constants

The similarities between Ga, In and Fe " are manifest in vivo by the binding of all three ions to the serum protein transferrin, Tf, normally used for iron transpQit. The formation constant for the Ga -Tf complex has been found to be and Welch has calculated values for the equilibrium constants for the exchange of trivalent metal ions between EDTA or DTPA and Tf as shown in Table 19. These figures show that only the DTPA complex of Ga is stable with respect to metal exchange with Tf. Table 19 also shows values for the equilibrium exchange reaction between Tf and hydroxide ion. These indicate that, while the indium-Tf complex should be stable to hydrolysis in vivo, in the long term the insoluble Ga(OH)3 should form from the... 

Hexa.cya.no Complexes. Ferrocyanide [13408-63 ] (hexakiscyanoferrate-(4—)), (Fe(CN) ) , is formed by reaction of iron(II) salts with excess aqueous cyanide. The reaction results in the release of 360 kJ/mol (86 kcal/mol) of heat. The thermodynamic stabiUty of the anion accounts for the success of the original method of synthesis, fusing nitrogenous animal residues (blood, horn, hides, etc) with iron and potassium carbonate. Chemical or electrolytic oxidation of the complex ion affords ferricyanide [13408-62-3] (hexakiscyanoferrate(3—)), [Fe(CN)g] , which has a formation constant that is larger by a factor of 10. However, hexakiscyanoferrate(3—) caimot be prepared by direct reaction of iron(III) and cyanide because significant amounts of iron(III) hydroxide also form. Hexacyanoferrate(4—) is quite inert and is nontoxic. In contrast, hexacyanoferrate(3—) is toxic because it is more labile and cyanide dissociates readily. Both complexes Hberate HCN upon addition of acids. 

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. " ... 

Neutral and Polymeric Aluminum and Iron. The association constants and enthalpies of aluminum and iron hydroxides have been evaluated by comparing the critically selected data of Baes and Mesmer (51) with that of R. M. Siebert and C. L. Christ (personal communication, 1976). Differences between the two data sets are negligible and the final selection was from Baes and Mesmer (51) because data on more complexes are found there. Important new species added to tjjie model are the polynuclear complexes Fe2(0H)2 and Fes(OH). Some controversy has arisen over the existence of Fe(0H) and A1(0H)3. Baes and Mesmer (51) have indicated that although the formation constant of A1(0H)3 is only known from one measurement (52) and has a large uncertainty, it is real, with a log K < -15.0 for the reaction... 

Any metal ion that has an EDTA formation constant higher than calcium or magnesium will interfere. Cyanide complexes strongly with copper, cobalt, nickel, zinc, and ferrous iron. Hydroxylamine or ascorbic acid is added to reduce iron to the ferrous state. If the solution is buffered to pH 10 before the indicator is added, then iron will not interfere because it precipitates as the hydroxide before it can react with the indicator or the EDTA. 

FORMATION CONSTANTS OF IRON HYDROXIDE AND CHLORIDE COMPLEXES... 

In an another stndy related to the additivity rule (Alessi and Fein 2010), the sorption of Cd(II) in mixtures of kaolinite. Bacillus subtilis bacterial cells, and iron oxy-hydroxide (HFO) was performed in the absence and presence of an organic ligand, acetate. The resnlts indicate that for systems containing B. subtilis, HFO, and kaolinite, the component additivity approach is a reasonable predictor of metal distribution, with the accuracy limited by the accuracy of the stability constants of the important surface complexes. However, in systems including acetate, the additivity rule predictions significantly nnderestimate the extent of adsorption above pH 5, likely due to the formation of ternary Cd-acetate surface complexes on each surface. 

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