On the complex formation equilibria between iron (III) and sulfate ions

The equilibria have been investigated at 25 degrees C in 3 M NaClO4 using potentiometry, glass and redox Fe3+/Fe2+ half-cells, and UV optical absorptiometry. The concentration of the reagents was chosen in the intervals: 10(-4) < or = [Fe(III)] < or = 5.10(-3) M, 0.01 < or = [SO4(2-)]tot < or = 0.65 M. The value of [H+] was kept at 0.1 M or more to reduce the hydrolysis of the Fe3+ ion to less than 1%. Auxiliary constants, corresponding to the formation of Fe(II)-sulfate complexes and to the association of H+ with SO4(2-) ions, were taken from previous determinations. The experimental data could be explained with the equilibria [formula: see text] Equilibrium constants at infinite dilution, log beta 101 degrees = 3.82 +/- 0.17, log beta 102 degrees = 5.75 +/- 0.17 and log beta 111 degrees = 3.68 +/- 0.35, have been evaluated by applying the specific interaction theory.     

The leaching kinetics of brannerite ore in sulfate solutions with iron(III)

A kinetic study of the leaching of powdered brannerite ore by sulfuric acid has been investigated. The effects of stirring speed ranging from 100 to 1,000?min^?1, particle size ranging from 20 to 120???m, concentration of Fe(III) ranging from 0.0025 to 0.20?M, acid concentration ranging from 0.1 to 2.0?M and temperature ranging from 15 to 90?°C on uranium dissolution are reported. The dissolution rate was founded to be significantly influenced by the temperature and concentration of the acid in solution. The experimental data for the dissolution rates of uranium have been analyzed with the shrinking-core model for reaction control. The apparent activation energy for the dissolution of uranium has been evaluated using the Arrhenius expression.     

Complex formation equilibria in iron(III)-L-alanine system

Summary Complex formation in iron(III)-L-alanine solutions was studied by emf glass electrode and spectrophotometric measurements, in 0.5 mol dm ^–3 (Na)NO₃ medium, at 25 ° C. In the concentration range 0.5 [Fe]₀ 20.0, 5.0 [Ala]₀ 1000.0 (mmol dm^–3) and 1.0 -log [H⁺] 3.5; {[Ala]/[Fe] = 10:1-100:1| the equilibria in the title system were explained by the model including the species FeHL, FeL, Fe(OH)L, Fe₂(OH)₂L₂ (where HL denotes L-alanine) and several hydrolytic products. The stability constants of complexes are given. The mechanism of formation and structure of complexes in solution is proposed.Abbreviations Ala alaninate ion - HAla alanine (zwitterion) - AlaH alanine (neutral) - H₂Ala⁺ alanine cation     

Catalytic promiscuity of an iron(II)–phenanthroline complex

A mononuclear iron(II) complex, [Fe(phen)₃]Cl₂ ( 1 ) (phen =1,10‐phenanthroline), has been synthesized in crystalline phase and characterized using various spectroscopic techniques including single crystal X‐ray diffraction. Crystal structure analysis revealed that 1 crystallizes in a monoclinic system with C2/m space group. Complex 1 acts as a functional model for a biomimetic catalyst promoting the aerobic oxidation of 3,5‐di‐tert ‐butylcatechol (3,5‐DTBC) through radical pathways with a significant turnover number (k _cat =3.55 × 10³ h⁻¹) and exhibits catechol dioxygenase activity towards the same 3,5‐DTBC substrate at room temperature in oxygen‐saturated ethanol medium. The existence of an isobestic point at 610 nm from spectrophotometric data indicates the presence of Fe³⁺ −3,5‐DTBC adduct favouring an enzyme–substrate binding phenomenon. Upon stoichiometric addition of 3,5‐DTBC pretreated with two equivalents of triethylamine to the iron complex, two catecholate‐to‐iron(III) ligand‐to‐metal charge transfer bands (575 and 721 nm) are observed and the in situ generated catecholate intermediate reacts with dioxygen (k _obs =9.89 × 10⁻⁴ min⁻¹) in ethanol medium to afford exclusively intradiol cleavage products along with a small amount of benzoquinone, and a small amount of extradiol cleavage products, which provide substantial evidence for a substrate activation mechanism. Copyright © 2016 John Wiley & Sons, Ltd.     

Aqua(nitrilo­triacetato)­(1,10‐phenanthroline)iron(III) monohydrate: a seven‐coordinate iron(III) complex

Reaction of 1,10‐phenanthroline (phen) with iron trichloride in the presence of sodium nitrilo­tri­acetate (NTA) resulted in the formation of red crystals of the title complex, [Fe(C₆H₆NO₆)(C₁₂H₈N₂)(H₂O)]·H₂O. The Fe atom has a distorted capped trigonal prismatic coordination comprised of one tetradentate NTA, one bidentate phen molecule and a water mol­ecule. Intermolecular O—H?O hydrogen bonds link the mol­ecules into infinite chains. The chains are crosslinked by hydrogen bonds involving the solvent water mol­ecule, leading to an infinite ladder packing mode.     

5‐n‐Butylpyridine‐2‐carboxylate–copper(II) and –iron(III) complexes

In trans‐bis(5‐n‐butyl­pyridine‐2‐carboxyl­ato‐κ²N,O)­bis­(methanol‐κO)copper(II), [Cu(C₁₀H₁₂NO₂)₂(CH₄O)₂], the Cu atom lies on a centre of symmetry and has a distorted octahedral coordination. The Cu—O(methanol) bond length in the axial direction is 2.596 (3) Å, which is much longer than the Cu—­O(carboxylate) and Cu—N distances in the equatorial plane [1.952 (2) and 1.977 (2) Å, respectively]. In mer‐tris(5‐n‐bu­tyl­pyridine‐2‐carboxyl­ato‐κ²N,O)­iron(III), [Fe(C₁₀H₁₂NO₂)₃], the Fe atom also has a distorted octahedral geometry, with Fe—O and Fe—N bond‐length ranges of 1.949 (4)–1.970 (4) and 2.116 (5)–2.161 (5) Å, respectively. Both crystals are stabilized by stacking interactions of the 5‐n‐butyl­pyridine‐2‐carboxyl­ate ligand, although hydrogen bonds also contribute to the stabilization of the copper(II) complex.     

The decomposition of iron(III) sulfate in air

The decomposition of initially hydrated powders of iron(III) sulfate was carried out in air over the temperature range 823–923 K. The decomposition process, which gave Fe₂O₃ as a solid product, was seen to have zero-order kinetics and an activation energy of 219 kJ·mol^–1. The nature of the product and the kinetics of decomposition were the same for samples decomposed in air and in argon. Sulfate samples with additives of FeS and Fe₂O₃ were also decomposed under similar conditions and the results confirmed the zero-order kinetics (for the case of the Fe₂O₃ additives) and the lack of effect of FeS on the decomposition of iron(III) sulfate.

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Zusammenfassung Anfänglich hydratiertes Eisen(III)-sulfatpulver wurde in Luft im Temperaturbereich 823–923 K zersetzt. Für die Reaktionsordnung des Zersetzungsprozesses, der als Endprodukt festes Fe₂O₃ lieferte, wurde Null und für die Aktivierungsenergie 219 kJ·mol^–1 ermittelt. Die Art des Produktes und der Kinetik der Zersetzung war in Luft und Argon gleich. Unter den gleichen Bedingungen wurden auch Sulfatproben mit Zusätzen von FeS und Fe₂O₃ zersetzt. Die Ergebnisse bekräftigen sowohl die nullte Reaktionsordnung (im Falle von Fe₂O₃ Zusätzen) als auch einen fehlenden Einfluß von FeS auf die Zersetzung von Eisen(III)-sulfat.

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823–923 . , , , 219 · ^–1. . FeS Fe₂O₃ . ( Fe₂O₃) - .

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This work was supported by a grant from the U.S. Department of Energy, Office of Basic Energy Sciences. The authors gratefully acknowledge this support.     

Hydroxo sulfate complexes of iron (III) in solution

The ternary Fe (III)-OH(-)-SO4(2-) complexes have been investigated at 25 degrees C in 3 M NaClO4 by potentiometric titration with glass electrode. The metal and sulfate concentrations ranged from 2.5 x 10(-3) to 0.03 M and from 5.10(-3) to 0.060 M, respectively. [H+] was decreased from 0.05 M to incipient precipitation of basic sulfate which occured at log[H+] between -2.3 and -2.5 depending on the concentration of the metal. For the interpretation of the data stability constants of HSO4(-), of binary hydroxo complexes (FeOH2+, Fe(OH)2+, Fe2(OH)2(4+), Fe3(OH)4(5+), Fe3(OH)5(4+)) and of sulfate complexes (FeSO4+, FeHSO4(2+), Fe(SO4)2-) were assumed from independent sources. The data are consistent with the presence of FeOHSO4, log beta 1-11 = -0.49 +/- 0.03. Equilibrium constants are defined as beta pqr for pFe3+ +qH+ +rSO4(2-) [symbol: see text] FepHq(SO4)r3p+q-2r. No substantial better fit could be found by adding a second mixed complex. Only a slightly smaller agreement factor resulted introducing as minor ternary complex Fe3(OH)6(SO4)3(3-) with log beta 3-63 = -5.8 +/- 0.5. Its evidence, however, cannot be considered conclusive.     

Extraction and complex formation of iron(III) thiocyanates with monooctyl anilinobenzylphosphonate

The extraction of iron (III) from aqueous hydrochloric acid solutions containing an excess of thiocyanate ions with monooctyl anilinobenzylphosphonate (MOABP) dissolved in chloroform or petroleum ether, was studied by radiometric and spectrophotometric methods. Iron forms mixed thiocyanate-MOABP complexes that are soluble in organic solvents. The composition of the iron complexes was studied by Job's method and radiometrically. In addition, several iron complexes were isolated from the organic phase and analyzed. The following complexes have been identified: Fe(SCN)R₂·HR, Fe(SCN)R₂, Fe(SCN)₂R·3HR and Fe(SCN)₂R·HR (HR = MOABP).     

Study of terbium(III)–dextran and terbium(III)–α-methyl glucoside interactions

The interaction of dextran with terbium(III) was studied in aqueous solution, pH 3.0–6.6, by fluorescence and optical rotatory dispersion. The polysaccharide enhances Tb(III) fluorescence intensity when the system is excited at the 290-nm hypersensitive transition (⁷F₆ → ⁵H₄). The dextran rotatory power is decreased in the presence of the metal ion. The results indicate that a 38% maximum of the polymer repeat units are coordinated. Complex formation occurs with displacement of water from the cation coordination sphere by hydroxyl groups at the second and third carbon atoms of the pyranoside ring. As the pH increases, a more asymmetric complex is formed. The α-methyl glucoside, low molecular weight dextran analogue, interacts with Tb(III) less strongly than dextran. Fluorimetric titrations indicated that the order of binding ability to polysaccharide is Tb(III) > Al(III) > Ca (II). © 1993 John Wiley & Sons, Inc.     

A mixed‐valence iron complex of the antitumour drug 6‐mercaptopurine: tris(6‐mercaptopurine)iron(II) tetrachloroferrate(III) chloride

Single crystals of the title complex, tris(1,6‐di­hydro‐9H‐purine‐6‐thione‐N⁷,S)­iron(II) tetra­chloro­ferrate(III) chloride, [Fe(C₅H₄N₄S)₃][FeCl₄]Cl, were grown on the surface of solid 6‐mercaptopurine monohydrate pellets in a solution of iron(III) chloride. The solution of the hexagonal structure required the application of twin refinement techniques. All the component ions lie on threefold rotation axes. The complex contains distorted octahedral [Fe(C₅H₄N₄S)₃]²⁺ cations with three N7/S6‐chelating neutral 6‐mercaptopurine ligands, tetrahedral [FeCl₄]^? anions with a mean Fe—Cl distance of 2.189 (1) Å, and free chloride ions.     

Decomposition kinetics of iron (III)-diclofenac compound

Non-isothermal decomposition of iron (III)-diclofenac anhydrous salt was investigated by thermogravimetry (TG) under different conditions in opened and closed α-alumina pans under nitrogen atmosphere. To estimate the activation energy of decomposition, the Capela and Ribeiro isoconversional method was applied. The results show that due to the lid cover different activation energies were obtained. From these curves a tendency can be seen where the plots maintain the same profile for closed lids and almost run parallel to each other. Independently of the different experimental conditions no remarkably different results have been obtained.     

A solution study of complex formation between iron(III) and oxalate in dimethylsulphoxide

Summary The complex formation between iron(III) and oxalic acid (ethanedioic acid, H₂ox) has been studied by potentiometry in dimethylsulphoxide (dmso) solution. H₂ox behaves as a weak diprotic acid in such a solvent, with overall association constants: log _j1=8.551(3) and log _j2=14.242(3) at 25°C and 0.1 Mn-Bu₄NClO₄. A reliable set of overall stability constants for the iron(III)-oxalato complexes, log ₁₁=13.16(4), log ₁₂=23.66(4) and log ₁₃=30.75(4), have been obtained for the first time under identical conditions. The electrochemical behaviour of such complexes was studied in dmso at a platinum electrode. The coordination ability of oxalate towards iron(III) in dmso and water media is compared and discussed in the light of thermodynamic and structural parameters.     

Cyclotrimerization of acetylene by the tris(acetylacetonato)titanium(III)–diethylaluminum chloride system

Reaction of acetylene with tris(acetylacetonato)titanium(III) and diethylaluminum chloride system leads to formation of benzene, a trace of ethylbenzene, and a small amount of polyacetylene. The isotopic composition of products obtained from cyclotrimerization of acetylene-d₂ and an equimolar mixture of acetylene and acetylene-d₂ is investigated to elucidate the mechanism of the cyclotrimerization. The results suggest a mechanism in which an acetylene inserts into the metal—ethyl bond formed by reaction of Ti(acac)₃ and Al(C₂H₅)₂Cl, followed by insertion of two acetylene molecules and elimination of a hydrogen atom from the first inserted acetylene to yield an ethylbenzene and a metal hydride intermediate. The metal hydride intermediate catalyzes acetylene cyclotrimerization to give benzene. During the reaction, the hydrogen atom in the metal hydride intermediate does not exchange with the hydrogen atom in the inserted acetylene molecules.     

Synthesis and magnetism of the first tetranuclear copper(II)–iron(III) complexes of macrocyclic oxamides

Four novel tetranuclear macrocyclic complexes of the formula [(CuLⁱ)₃Fe](ClO₄)₃·3H₂O (i=1–4, Lⁱ are the dianions of the [14]N₄ and [15]N₄ macrocyclic oxamides, namely 2,3-dioxo-5,6:13,14-dibenzo-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene, 2,3-dioxo-5,6:13,14-dibenzo-9-methyl-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene and 2,3-dioxo-5,6:14,15-dibenzo-7,13-bis(ethoxycarbonyl)-1,4,8,12-tetraazacyclotetradeca-7,12-diene] have been prepared and characterized. These complexes are the first examples of oxamido-bridged Cu(II)–Fe(III) heterometallic species. Cryomagnetic studies on [(CuL¹)₃Fe](ClO₄)₃·3H₂O (1) and [(CuL³)₃Fe](ClO₄)₃·3H₂O (3) (77–300 K) revealed that the Cu(II) and Fe(III) ions interact antiferromagnetically through the oxamido bridge, with the exchange integral J=−30.8 cm⁻¹ for 1 and J=−28.7 cm⁻¹ for 3 based on . The interaction parameters have been compared with that of the related [Cu₃Mn] compound.     

Isolatable Organophosphorus(III)–Tellurium Heterocycles

A new structural arrangement Te₃(RP^III)₃ and the first crystal structures of organophosphorus(III)–tellurium heterocycles are presented. The heterocycles can be stabilized and structurally characterized by the appropriate choice of substituents in Te_m(P^IIIR)_n (m=1: n=2, R=OMes* (Mes*=supermesityl or 2,4,6‐tri‐tert‐butylphenyl); n=3, R=adamantyl (Ad); n=4, R=ferrocene (Fc); m=n=3: R=trityl (Trt), Mesor by the installation of a P^V₂N₂ anchor in RP^III[TeP^V(tBuN)(μ‐NtBu)]₂ (R=Ad, tBu).