Iron hydroxide complexes, formation

In the wetlands of Idaho, the formation of an Fe(III) precipitate (plaque) on the surface of aquatic plant roots (Typha latifolia, cat tail and Phalaris arundinacea, reed canary grass) may provide a means of attenuation and external exclusion of metals and trace elements (Hansel et al, 2002). Iron oxides were predominantly ferrihydrite with lesser amounts of goethite and minor levels of siderite and lepidocrocite. Both spatial and temporal correlations between As and Fe on the root surfaces were observed and arsenic existed as arsenate-iron hydroxide complexes (82%). 

Iron(II) formate dihydrate, 14 537 Iron(II) fumarate, 14 537 Iron gelbs, 19 399, 400 Irondl) gluconate dihydrate, 14 541 Iron group carbides, 4 690-692 Iron halides, 14 537-540 Iron hydroxide, water exchange rates and activation parameters of hexaaqua complexes, 7 589t Iron(II) hydroxide, 14 542 Iron(III) hydroxide, 14 542 Iron hydroxides, 14 541—542 Iron(II) iodide, 14 540 Iron(III) iodide, 14 540 Iron/iron alloy plating, 9 813—814. See also Fe entries... 

A review of iron(III) in aqueous solution covers hydrolysis and polymerization, the formation and dissociation of binuclear species, and kinetics and mechanisms of water exchange and complex formation. " Kinetic and equilibrium data for hydrolytic reactions of iron(III) have been conveniently assembled. Reviews of hydrolysis of Fe aq, and subsequent precipitation of hydrated oxide-hydroxide species, cover a very wide range of media, from geochemistry to biology to human metabolism. Added anions or pH variation can affect which form... 

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. " ... 

The formation of -butyldiazoate by reaction of [Fe(CN)5(NO)]2 with lithium -butyl amide contrasts with the formation of dibutylamine as the main product in the reaction of the same complex with -butylamine (85). This can be explained if the diazoic/diazoate equilibrium shown in Fig. 18 is shifted to the left far enough to form of a diazenido by loss of hydroxide. Attack of -butylamine on the a-carbon of the diazenido species, produces dibutylamine. DFT computed results suggest that the stabilization by complexation of the intermediate diazonium ion (see Fig. 18) is large for the iron-pentacyano complex, in agreement with the fact that no rearrangement products were observed in the reaction of this species with -butylamine (86). The reaction has been proposed as a good route for the preparation of symmetrical, unsymmetrical, and cyclic secondary amines (85). 

A final example concerns the formation of heteropolynuclear hydroxide complexes.116 The complexes [(OH)Fe(OH)2Cr]3+, [(OH)Fe(OH)2Cr(OH)]2+ and [(OH)2Fe(OH)2Cr(OH)]+, or polymers such as Fe(OH)2M "+ (M = V, Cr, Mn, Co, Ni, Cu n = 2-4) have been studied with a view to an understanding of the inclusion of transition metals in iron ores as mixed oxides rather than their occurrence as discrete mineral phases. Many other examples might have been chosen in this section. Reference should be made to the general reviews given above. However it should be clear that simple inorganic coordination complexes play a major role in the chemistry of natural aqueous systems at low temperatures. 

Virtually all microorganisms—with the exception of certain lactobacilli— require iron as cofactor of many metabolic enzymes and regulatory proteins because of its ability to exist in two stable oxidation states. Although iron is one of the most abundant elements in the environment, it is often a limiting factor for bacterial growth. This is so because of the formation of insoluble ferric hydroxide complexes under aerobic conditions at neutral pH, which impose severe restrictions on the availability of the element. Consequently, bacteria have evolved specialized high-affinity transport systems in order to acquire sufficient amounts of this essential element. 

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... 

Ferric Compounds. The hydrated ferric ion, Fe(H20)g+ + +, is pale violet in color. The ion loses protons very readily, however, and ferric salts in solution usually are yellow or brown, because of the formation of hydroxide complexes. Ferric nitrate, Fe(N03)3 6H20, exists as pale violet deliquescent crystals. Anhydrous ferric sulfate, Fe2(S04)g, is obtained as a white powder by evaporation of a ferric sulfate solution. A well-crystallized ferric sulfate is iron alum, KFe(S04)2 12H20, which forms pale violet octahedral crystals. 

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... 

The second-order term in the rate laws for reactions of low-spin iron(II) diimine complexes with such nucleophiles as hydroxide and cyanide ions has been established as arising from a bimolecular reaction between complex and nucleophile.182 Activation volumes that were obtained for reactions of CN and OH with Fc(phcn)2 1 and Fe(bpy)3 + were in the range of +19.7 to +21.5cm3mol-1.183 Because these observations were not readily accounted for by an associative mechanism, a mechanism analogous to the Eigen-Wilkins mechanism of complex formation was introduced in which dissociative activation dominates in determining the observed activation volumes. However, subsequently it was shown that solvation... 

FORMATION CONSTANTS OF IRON HYDROXIDE AND CHLORIDE COMPLEXES... 

Bonneviot L, Clause O, Che M, Manceau A, Dexpert H (1989b) EXAFS characterization of the adsorption sites of nickel ammine and ethyldiamine complexes on a silica surface. Catalysis Today 6 39-46 Bomebusch H, Clausen BS, Steffensen G, Liitzenkirchen-Hecht D, Frahm R (1999) A new approach for QEXAFS data acquisition. J Synchrotron Rad 6 209-211 Bostick BC, Fendorf S, Barnett MO, Jardine PM, Brooks SC (2002) Uranyl surface complexes formed on subsurface media from DOE facilities. Soil Sci Soc Am J (2002) 66 99-108 Bottero JY, Manceau A, Villieras F, Tchoubar D (1994) Structure and mechanisms of formation of iron oxide hydroxide (chloride) polymers. Langmuir 10 316-319 Bourg ACM, Joss S, Schindler PW, (1979) Ternary surface complexes 2. Complex formation in the system silica-Cu(II)-2,2 bipyridyl . Chimia 33 19-21... 

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