Extraction equilibrium between primary amine primene 81R and iron(III) sulphate

The extraction equilibrium between aqueous iron (III) sulphate solutions and amine Primene 81R was studied. The results show that the free amine extracts iron(III) from these solutions. The extracted complex has been isolated and can be represented by the stoichiometric formula 4RNH₂·Fe₂(SO₄)₃. The extraction reaction is almost independent of temperature and change in the diluent of the organic phase. On the basis spectral studies a structure for the extracted complex is suggested.     

Thermal analysis of iron(II) sulphate heptahydrate in air

Iron(II) sulphate hydrates (hexa- through mono-) have been prepared and their thermal decomposition behaviours have been studied in air by isothermal and dynamic thermal analysis methods. The results show that their behaviours are similar to that of the heptahydrate. The stepwise loss of water molecules is accompanied by oxidation. Under a restricted supply of oxygen, the anhydrous sulphate is oxidized directly to Fe₂O(SO₄)₂ without the formation of Fe(OH)SO₄. When free exchange with oxygen is allowed, Fe(OH)SO₄ is formed, which in turn decomposes to Fe₂O(SO₄)₂. The decomposition of Fe₂(SO₄)₂ to iron(III) oxide and sulphur oxides appears to occur via two independent paths — one direct and other through iron(III) sulphate.     

The extraction of iron(III) by dioctylarsinic acid in chloroform

Dioctylarsinic acid, HDOAA, in chloroform solution has been investigated as a reagent for the extraction of iron(III) chloride. The extraction coefficient reaches two maxima, one of 1.5 at 8.5 M hydrochloric acid and another of 7 at pH 2.3. Experiments in the range 4–8 M for sulfuric, nitric and perchloric acids showed no extraction of iron(III) from these solutions for extraction times of 6 h. Evidence for the extraction of H₃FeCl₆ from 4–9 M hydrochloric acid solutions as [(H₂DOAA)⁺]₃FeCl₆^3- is presented. The species extracted from aqueous solutions of pH 1–2.3 is probably a hydroxy complex of the composition [Fe₂(DOAA)₂(HDOAA)X₄(H₂0)₂ ](X = OH and/or Cl).     

Solvent extraction of metal ions from aqueous solutions containing N,N,N′,N′-ethylenediaminetetraacetic and related acids—II. La(III) and diethylenetriaminepentaacetic acid

In the absence of a competing anion, [La(DTPA)]²⁻ was extracted from aqueous phases in the pH ranges 1–3 by the perchlorate salt of the primary amine Primene JM-T. The addition of small amounts of SO²⁻₄ to the aqueous phases depressed the extraction of La to near zero. As the SO²⁻₄ concentration was increased further, D_La increased to values greater than that found in the absence of SO²⁻₄; this was caused by a change in the mechanism of extraction and [La(SO₄)₂]⁻ became the extracted species.     

Synthesis and properties of a monomeric and a μ-oxo-bridged dimeric iron(III) complex with a tetradentate pyridine amide in-plane ligand. X-ray structure of [Fe(bpc)Cl(DMF)] [H2bpc=4,5-dichloro-1,2-bis(pyridine-2-carboxamido)benzene]

The controlled nucleophilic halide displacement reaction of [NEt₄][Fe(bpc)Cl₂] [H₂bpc=4,5-dichloro-1,2-bis(pyridine-2-carboxamido) benzene] with AgClO₄ in MeCN afforded a crystalline iron(III) complex Fe(bpc)Cl·H₂O 1. The mixed chloro-dimethylformamide (DMF) axially ligated complex [Fe(bpc)Cl(DMF)] (obtained during recrystallization of 1 from DMF; however, it loses DMF quite readily to revert back to 1) has been structurally characterized. It belongs to only a handful of mononuclear high-spin iron(III) complexes having deprotonated picolinamide ligand. The iron(III) centre is co-ordinated in the equatorial plane by two pyridine nitrogens and two deprotonated amide nitrogens of the ligand, and two axial sites are co-ordinated by a chloride ion and a DMF molecule. The metal atom has a distorted octahedral geometry. Reaction of 1 with [ⁿBu₄N][OH] in MeOH afforded a μ-oxo-bridged diiron(III) complex, [Fe(bpc)]₂O·DMF·2H₂O, 2. The spin state and the co-ordination environment of the iron(III) centres in 1 and 2 have been determined by temperature-dependent (25–300 K) magnetic susceptibility measurements in the solid state (Faraday method) and Mössbauer spectral studies at 300 K. Complex 1 behaves as a perfect S=5/2 system, in the solid-state as well as in DMF solution. The two iron(III) centres in 2 are antiferromagnetically coupled (J=−117.8 cm⁻¹) and the bridged dimeric structure is retained in DMF solution. Bridge-cleavage reactions of 2 have been demonstrated by its ready reaction with mineral acids such as HCl and MeCO₂H to generate authentic S=5/2 complexes, [Fe(bpc)Cl₂]⁻ and [Fe(bpc)(O₂CMe)₂]⁻, respectively.     

The Effect of Concentration Parameters on Complexation in the Iron(0)–Iron(II)–Glycine–Water System

The processes of formation of iron(II) complexes in aqueous glycine solutions in the pH range of 1.0–8.0 at 298 K and ionic strength of 1 mol/L (NaClO₄) are studied using Clark and Nikolskii’s oxidation potential method. The type and number of coordinated ligands, the nuclearity, and the total composition of the resulting complexes are determined. The following complex species are formed in the investigated system: [Fe(OH)(H₂O)₅]⁺, [FeHL(H₂O)₅]²⁺, [Fe(HL)(OH)(H₂O)₄]⁺, [Fe(OH)₂(H₂O)₄]⁰, [Fe₂(HL)₂(OH)₂(H₂O)₈]²⁺, and [Fe(HL)₂(H₂O)₄]²⁺. Their formation constants are calculated by the successive iterations method using Yusupov’s theoretical and experimental oxidation function. The model parameters of the resulting coordination compounds are determined.     

Mechanistic study of cerium(IV) oxidation of antimony(III) in aqueous sulphuric acid in the presence of micro amounts of manganese(II) by stopped flow technique

The oxidation of antimony(III) by cerium(IV) has been studied spectrometrically (stopped flow technique) in aqueous sulphuric acid medium. A minute amount of manganese(II) (10⁻⁵ mol dm⁻³) is sufficient to enhance the slow reaction between antimony(III) and cerium(IV). The stoichiometry is 1:2, i.e. one mole of antimony(III) requires two moles of cerium(IV). The reaction is first order in both cerium(IV) and manganese(II) concentrations. The order with respect to antimony(III) concentration is less than unity (ca 0.3). Increase in sulphuric acid concentration decreases the reaction rate. The added sulphate and bisulphate decreases the rate of reaction. The added products cerium(III) and antimony(V) did not have any significant effect on the reaction rate. The active species of oxidant, substrate and catalyst are Ce(SO₄)₂, [Sb(OH)(HSO₄)]⁺ and [Mn(H₂O)₄]²⁺, respectively. The activation parameters were determined with respect to the slow step. Possible mechanisms are proposed and reaction constants involved have been determined.     

Synthesis, infrared spectra, thermal analyses and structural studies of half-sandwich Fe(III)/Fe(II) complex containing pyridine-2,6-dicarboxylate and 1,10-phenanthroline

A new pyridine-2,6-dicarboxylate iron(III)/iron(II) complex [Fe(phen)₃][Fe₂(PDC)₄]·3CH₃OH was synthesized and characterized (where PDC = pyridine-2,6-dicarboxylate, phen = 1,10-phenanthroline) by using elemental analysis, IR spectroscopy and thermal analyses (TGA and DTA). The molecular structure of the complex has been determined by single-crystal X-ray diffraction. The complex is mixed-ligands and the IR spectra display bands characteristic of coordinated mixed-ligand bases. All the IR results are in agreement with the X-ray crystal result. The bond lengths indicate that this complex has [Fe(phen)₃]²⁺ cation where Fe(II) ion is in typical low-spin state, and in counter ions, [Fe(PDC)₂]⁻ are both in high-spin state.     

Extraction studies on iron

The extraction of Fe(III) and Fe(II) from various aqueous acidic solutions, with nitrobenzene, Amberlite LA-2, TBP and HDEHP is described. Conditions are given for the separation of Fe(III) from Fe(II). The extraction and separation of Fe(III) and Fe(II) is most adequate from HCl solutions, using the four solvents. The extraction of iron halides from H₂SO₄ solutions has been studied. The effect of water-miscible alcohols on the distribution of Fe(III) and Fe(II) was also studied. Extraction equilibria and mechanisms were proposed on the basis of the obtained results.     

Reactivity of Ammonium Halides: Action of Ammonium Chloride and Bromide on Iron and Iron(III) Chloride and Bromide

Ammonium chloride and bromide, (NH₄)Cl and (NH₄)Br, act on elemental iron producing divalent iron in [Fe(NH₃)₂]Cl₂ and [Fe(NH₃)₂]Br₂, respectively, as single crystals at temperatures around 450 °C. Iron(III) chloride and bromide, FeCl₃ and FeBr₃, react with (NH₄)Cl and (NH₄)Br producing the erythrosiderites (NH₄)₂[Fe(NH₃)Cl₅] and (NH₄)₂[Fe(NH₃)Br₅], respectively, at fairly low temperatures (350 °C). At higher temperatures, 400 °C, iron(III) in (NH₄)₂[Fe(NH₃)Cl₅] is reduced to iron(II) forming (NH₄)FeCl₃ and, further, [Fe(NH₃)₂]Cl₂ in an ammonia atmosphere. The reaction (NH₄)Br + Fe (4:1) leads at 500 °C to the unexpected hitherto unknown [Fe(NH₃)₆]₃[Fe₈Br₁₄], a mixed‐valent Fe^II/Fe^I compound. Thermal analysis under ammonia and the conditions of DTA/TG and powder X‐ray diffractometry shows that, for example, FeCl₂ reacts with ammonia yielding in a strongly exothermic reaction [Fe(NH₃)₆]Cl₂ that at higher temperatures produces [Fe(NH₃)]Cl₂, FeCl₂ and, finally, Fe₃N.     

IR spectra and thermal decomposition/dehydration of double complex salts of lanthanum(III) sulphate complex anions with several cobalt(III) ammine complex cations

Double complex salts of lanthanum(III) sulphate complex anions with several cobalt(III) ammine complex cations, [Co(NH₃)₆][La(SO₄)₃]·H₂O (1), (NH₄)₃[Co(NH₃)₅ H₂O]-[La(SO₄)₃]₂·2H₂O (2), and (NH₄)₃[Co(NH₃)₄(H₂O)₂][La(SO₄)₃]₂·2H₂O (3), were prepared by the addition of hexaamminecobalt(III), pentaammineaquacobalt(III), and cis- tetra-amminediaquacobalt(III) complexes to the solution containing lanthanum(III) ion and excess ammonium sulphate. The IR spectra of sulphate groups of these double complex salts were much more complicated than those of the almost free sulphate groups such as (NH₄)₂SO₄ and [Co(NH₃)₆]₂(SO₄)₃·5H₂O. Furthermore, values of activation energy in the dehydration process of 1, 2 and 3 were estimated using modified Doyle's and Wiedemann's method. They were 95.6 ± 4.3, 157.1 ± 15.5 and 163.2 ± 20.8 kJ mol^?1, respectively. Here, one molecule water is released per molecule of 1, 2 and 3.     

Extraction,complex formation and spectrophotometric determination of iron(III) with 2-carbethoxy-5-hydroxy-1-(4-tolyl)-4-pyridone

Summary The extraction of iron(III) from aqueous HCl, H₂SO₄, HClO₄, HNO₃ solutions by 2-carbethoxy-5-hydroxy-1-(4-tolyl)-4-pyridone (HA) dissolved in CHCl₃ has been studied. Quantitative extraction of iron(III) is achieved if the concentration of the acids does not exceed 1N. The composition of the iron (III)—HA complex formed in the organic phase was investigated spectrophotometrically, radiometrically and by analysis of the isolated species. In the aqueous phase iron (III) and HA form three different complexes, depending on the initial iron: HA concentration ratio and the pH of the solution. They are the violet FeA²⁺, the orange-red FeA₂ ⁺ and the orange-yellow FeA₃. The latter is identical with the complex found in the organic phase, which was isolated as a solid crystalline material and characterized by elemental analysis and infrared spectroscopy. A spectrophotometric method for the determination of iron(III) in the aqueous phase and in the chloroform solution, by extraction with HA, is described.

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Zusammenfassung Die Extraktion von Fe(III) aus wäßrigen Lösungen von HCl, H₂SO₄, HClO₄ oder HNO₃ mit 2-Carbäthoxy-5-hydroxy-1-(4-tolyl)-4-pyridon (HA) in chloroformischer Lösung wurde untersucht. Sie verläuft quantitativ, wenn die Konzentration der Säure nicht größer ist als 1-n. Die Zusammensetzung des Fe(III)-HA-Komplexes in der organischen Phase wurde spektrophotometrisch, radiometrisch und durch Analyse der isolierten Substanz untersucht. In wäßrigem Milieu bilden Eisen(III) und HA drei verschiedene Komplexe je nach dem anfänglichen Konzentrationsverhältnis Fe(III): HA und je nach dem pH der Lösung. FeA²⁺ ist violett, FeA₂ ⁺ ist orange-rot und FeA₃ orangegelb. Diese Verbindung ist mit dem in der organischen Phase gefundenen Komplex identisch, der in kristallisierter Form isoliert und durch Elementaranalyse und IR-Spektrometrie charakterisiert wurde. Eine spektrophotometrische Methode zur Eisen(III)-Bestimmung in wäßriger Phase und in chloroformischer Lösung durch Extraktion mit HA wurde beschrieben.

     

Mechanism for the radiolytic conversion of sulphur dioxide to sulphuric acid

The present paper describes the radiolytic oxidation of 10^-4M K₄[Fe(CN)₆] aqueous aerated solution in the presence of different concentrations of SO₂. In the absence of SO₂, ferrocyanide is oxidized to ferricyanide with a G value of 7.2. In this solution two O₂^- react to form H₂O₂. Ferrocyanide is oxidized by OH and H₂O₂ both. At low concentration of SO₂, O₂^- reacts with SO₂ forming first SO₄^._, which leads to chain oxidation of SO₂. The G [Fe(CN)₆^3-) decrease from 7.2 to 4.5. At higher concentrations of SO₂, H₂O₂ also reacts with SO₂ and the G(Fe(CN)₆^3-] further reduces to 2.7. In the presence of chloride ions, SO₄^._ converts them to chloride atoms which react with H₂O₂ and ferrocyanide and the G[Fe(CN)₆^3-] is again increased to 4.3. The reaction of OH with SO₂ was observed only at high concentrations of SO₂ since the reaction of OH with ferrocyanide is very fast. The importance of water and ammonia in the conversion of sulphur dioxide to sulphuric acid probably lies in their reaction with SO₄^2- to form H₂SO₄ or (NH₄)₂SO₄.     

Solvatochromism and solvation of ternary iron-diimine-cyanide complexes

Summary The solvatochromic behaviour of several complexes [Fe(LL)₂(CN)₂] with LL=Schiff base diimine has been established in a series of non-aqueous solvents, as has that of two analogues containing diazabutadiene ligands. Transfer chemical potentials have been derived from appropriate solubility measurements for several iron(II)-and iron(III)-diimine-cyanide complexes into aqueous methanol, and for [Fe(bipy)₂(CN)₂] into several binary aqueous solvent series. The usefulness of solvatochromic shifts and transfer chemical potentials as indicators of selective solvation is discussed. Kinetics of oxidation of catechol and of 4-t-butyl catechol by [Fe(bipy)(CN)₄]^– in aqueous solution are described.     

Solvent extraction of zinc by 2-hexylpyridine in benzene from aqueous mineral acid — Thiocyanate media

Solvent extraction of Zn(II) by 2-hexylpyridine (HPy) in benzene has been studied from aqueous mineral acid—thiocyanate media. The extraction, though dependent on the acidity of the aqueous phase, is poor from mineral acids (HCl, HNO₃ or H₂SO₄). Addition of 0.02M KSCN to the aqueous phase enhances the distribution ratio by a factor of almost one thousand. The stoichiometry of the extracted complex established by the usual slope analysis method indicates that an ionic type complex, e.g. Zn(SCN)₄·(HPyH)₂, is responsible for extraction. Complexing anions like acetate, oxalate or citrate at 1 M concentration mask the extraction of Zn(II) almost completely. Separation factors determined at optimal conditions (0.1M HPy in benzene −0.05M H₂SO₄+0.2M SCN⁻) indicate that Zn(II), along with Hg(II), can be separated in a single extraction from a number of metals, e.g. Cs(I), Sr(II), Ln(III), Y(III), Cr(III) and (VI). Other metals of interest like Cu(II), Co(II), Fe(III), Mo(VI), U(VI) and Tc(VII) are coextracted but the separation factors are large enough to allow separation in a multistage extraction process.     

Solution Properties of Azidokojatoiron(III) Complexes

The formation of iron(III) complexes with chelating azidokojate anions L⁻ was investigated in aqueous solutions as a function of the pH and the c(Fe³⁺):c(HL) molar ratio. Based on the stability constants, the distribution among the above complexes, [Fe(H₂O)₆]³⁺, and [Fe(H₂O)₅(OH)]²⁺ were calculated in solutions of various compositions. The complexes are redox stable in aqueous solutions both in the dark and in visible laboratory light. Properties of the investigated azidokojic acid and its iron(III) complexes are compared with those required for therapeutic applications as alternative iron chelators.     

Solvent extraction studies of plutonium(IV) and americium(III) in room temperature ionic liquid (RTIL) by di-2-ethyl hexyl phosphoric acid (HDEHP) as extractant

Solvent extraction of Pu(IV) and Am(III) from aqueous nitric acid into room temperature ionic liquid (RTIL) by an acidic extractant HDEHP (di-2-ethyl hexyl phosphoric acid) was carried out. The D values indicated substantial extraction for Pu(IV) and poor extraction for Am(III) at 1M aqueous nitric acid concentration. However at lower aqueous nitric acid concentrations (pH 3), the Am(III) extraction was found to be quantitative. The least squares analysis of the extraction data for both the actinides ascertained the stoichiometry of the extracted species in the RTIL phase for Pu(IV) and Am(III) as [PuH(DEHP)₂]³⁺, AmH(DEHP)²⁺. From the D values at two temperatures, the thermodynamic parameters of the extraction reaction for Pu(IV) was calculated.     

Iron(III) activation hits a [4 + 4] macrocycle

The tetranuclear complex [Fe(III)2(L')(OH)(CH3O)]2, 1, has been synthesised from the reaction of either ferrous [in excess as 4:1 or stoichiometric 2:1 iron(II) : H4L] or ferric ions [4:1 iron(III) : H4L] with the large macrocycle, H4L, using aerobic conditions in methanol in the presence of triethylamine. The structure of 1 was determined by single-crystal X-ray diffraction. These reaction conditions lead to the modification of the original macrocycle through the incorporation of a methylene group between two amine groups to give an imidazolidine ring in (L')4-. The controlled addition of formaldehyde into the reaction system results in a significantly improved yield of 1, suggesting that it is involved in the reaction mechanism. The (L')4- macrocycle binds to two, well-separated, iron(III) centres [Fe(1)...Fe(1a) > 8 A]. Each iron(III) centre is further linked via hydroxy and methoxy bridges to equivalent iron(iii) centres contained in a second macrocycle. Overall this gives a structure containing two {Fe(OH)(CH(3)O)Fe} dimers [Fe(1)...Fe(2)ca. 3.2 A] sandwiched by two (L')4- macrocycles. The complex was further characterised by SQUID magnetic measurements and can be interpreted in terms of two isolated antiferromagnetically coupled Fe(III) dimers (J=-23.75 K).     

Reduction Dehydration of Iron Oxide Hydroxide by iron metal in aqueous medium

The reductive dehydration of iron hydroxide (FeOOH) by iron metal in aqueous solutions of ferrous sulphate was found to occur. These reactions of α, β, γ FeOOH and Fe(OH)₃ · nH₂O respectively were carried out in 0.01–1 mol iron(II) sulphate solutions and over the temperature range of 80–100°C to produce Fe₃O₄ in all cases. The reaction rate decreases with increasing Fe²⁺ concentration and depends on the total concentration of sulphate anion. The presence of iron(II) chloride has an inhibiting effect.     

Electronic structure and spectra of [Fe(CN)6SO3]4−

The complex ion [Fe(CN)₆SO₃]⁴⁻ has been prepared in aqueous solution and as the zinc salt in the solid state. The electronic and IR spectra of the complex ion (I) have been recorded. MO calculations have been performed to understand the electronic structure of complex I. The electronic spectra of I and hexacyanoferrate(II) [HCF(II)] have been calculated and compared with the experimental results for I, HCF(II) and HCF(III). The experimental and theoretical results suggest that the oxidation state of Fe in I is + 3 and not +2 and the SO₃ moiety is bonded to one of the nitrogen atoms of the cyano group.