Spectrophotometric determination of iron(III) with EDTA tetrahydrazide

The tetrahydrazide of ethylenediamine tetraacetic acid (NH₂NH)₄-EDTA was synthesized from the EDTA ester and hydrazine hydrate in ethanolic solution, the resulting (NH₂NH)₄-EDTA being recrystallized in 60% ethanol. When the spectrophotometric study of the iron(III) (NH₂NH)₄-EDTA complex in aqueous solution was made two absorption maxima at 530 and 450 nm at pH 4.5 and 11.0, respectively, were found. Beer's law is obeyed in the range 1.0–20.0 μg Fe(III) ml^?1 at 530 nm and pH 4.5 and 0.5–12.0 μg Fe(III) ml^?1 at 450 nm and pH 11.0, the molar absorptivities being 1.95 × 10³ 1 mol^?1 cm^?1 at 530 nm and 3.35 × 10³ 1 mol^?1 cm^?1 at 450 nm, respectively. The Ringbom optimal interval falls between about 3 and 18 μg Fe(III) ml^?1 at 530 nm and about 2–14 μg Fe(III) ml^?1 at 450 nm. The reaction between the metal and the ligand was also investigated. The method has been successfully applied to the determination of iron in talcs.     

Metal complexes of pyrimidine derived ligands – Syntheses,characterization and X-ray crystal structures of Ni(II), Co(III) and Fe(III) complexes of Schiff base ligands derived from S-methyl/S-benzyl dithiocarbazate and 2-S-methylmercapto-6-methylpyrimidine-4-carbaldehyde

Two new pyrimidine based NNS tridentate Schiff base ligands S-methyl-3-((2-S-methyl-6-methyl-4-pyrimidyl)methyl)dithiocarbazate [HL₁] and S-benzyl-3-((2-S-methyl-6-methyl-4-pyrimidyl)methyl)dithiocarbazate [HL₂] have been synthesised by the 1:1 condensation of 2-S-methylmercapto-6-methylpyrimidine-4-carbaldehyde and S-methyl/S-benzyl dithiocarbazate. A Ni(II) complex of HL₁ and Co(III) and Fe(III) complexes of HL₂ have been prepared and characterized by elemental analyses, molar conductivities, magnetic susceptibilities and spectroscopic studies. All the bis-chelate complexes have a distorted octahedral arrangement with an N₄S₂ chromophore around the central metal ion. Each ligand molecule binds the metal ion using the pyrimidyl and azomethine nitrogen and thiolato sulfur atoms (except in the nickel complex, one ligand molecule uses the thione sulfur in lieu of thiolato sulfur atom). In the Ni(II) complex, one of the ligand molecules behaves as a neutral tridentate and the other molecule functions as a uninegative tridentate, whereas in the Co(III) and Fe(III) complexes, the ligand molecules behave as monoanionic tridentate. All the complexes were analyzed by single crystal X-ray diffraction and significant differences concerning the distortion from an octahedral geometry of the coordination environment were observed.     

Spectrophotometric determination of cobalt in iron-, cobalt- and nickel-base alloys

A spectrophotometric method has been developed for the accurate determination of cobalt at milligram level, based on oxidation of the cobalt(II)-EDTA complex with gold(III) chloride at pH 4.0-6.5 and 100 degrees and measurement of the absorbance of the resultant violet cobalt(III)-EDTA complex at 535 nm. The precision is not affected by the presence of several metal ions; including coloured ones such as Cu(II), Ni(II) and Fe(III). However, chromium(III) interferes since it also forms a violet complex with EDTA, but can be removed by separation with pyridine. Practical application of the method is illustrated by the determination of cobalt in alloys based on iron, cobalt and nickel. Over the cobalt range 8-52% the error ranges from 0.1 to 0.3%.     

Bis-chelate Fe(III) complex of an azomethine at the focal point of a branched ester functionalized with cyclohexylbenzoic acid

A Fe(III) complex with Cl counter ion based on a branched Schiff base has been synthesized and studied. The compound was produced by the reaction of the Schiff base with FeCl₃ at room temperature in benzene–ethanol. The complex is symmetric, i.e., bis-chelate, with an octahedral coordination of Fe. The compound revealed phase transitions of the “solid–solid” type. The complex displayed a temperature-induced spin transition (S?=?1/2???5/2) which was detected by EPR.     

Heme Fe?SO2− intermediates in sulfite reduction: Contrasts with Fe?OO2− species from oxygen–oxygen bond activating systems

Sulfite reductase (SiR) catalyzes a six electron and six proton reduction of sulfite to sulfide. Similarly to the cytochrome P450 (cytP450) family, the active site in SiR contains a (partially reduced) heme bound axially to a cysteinate ligand—though with an extra Fe₄S₄ cluster. Fe(III) SO²⁻, Fe(III) SOH⁻, and Fe(III) SO(H₂) intermediates have been proposed for the catalytic cycle of SiR, leading to a formally Fe(V)S species—akin to the widely accepted reaction mechanism in cytP450. Here, density functional theory (DFT) data is reported for of such FeSO(H₂) intermediates. The Fe(III) SO²⁻ models display relatively high energies for homolytic bond breaking compared to their isomeric oxygen‐bound Fe(III) OS²⁻ models, and thus offer a better alternative in terms of avoiding radical side products able to induce enzyme suicide. This could be due to the fact that the (iron‐bound) sulfur is more active from a redox standpoint compared to oxygen, thus permitting the departing oxygen to maintain a redox‐inert state. Di‐protonation of the oxygen is computed to lead to a compound I type Fe(IV)S coupled to a porphyrin radical anion—consistent with an intermediate previously observed by x‐ray crystallography.     

Formation of Tc(III)-EDTA complex

Tc(III)-EDTA complex has been synthesized by the ligand substitution reaction of hexakis-(thiourea) technetium(III) ion with EDTA. The complex exhibits absorption maxima at 368 and 470 nm. The formation reaction proceeds predominantly as follows:

Environmental Mobility of Pu(IV) in the Presence of Ethylenediaminetetraacetic Acid: Myth or Reality?

Ethylenediaminetetracetic acid (EDTA), which was co-disposed with Pu at several US Department of Energy sites, has been reported to enhance the solubility and transport of Pu. It is generally assumed that this enhanced transport of Pu in geologic environments is a result of complexation of Pu(IV) with EDTA. However, the fundamental basis for this assumption has never been fully explored. Whether EDTA can mobilize Pu(IV) in geologic environments is dependent on many factors, chief among them are not only the complexation constants of Pu with EDTA and dominant oxidation state and the nature of Pu solids, but also (1) the complexation constants of environmentally important metal ions (e.g., Fe, Al, Ca, Mg) that compete with Pu for EDTA and (2) EDTA interactions with the geomedia (e.g., adsorption, biodegradation) that reduce effective EDTA concentrations available for complexation. Extensive studies over a large range of pH values (1 to 14) and EDTA concentrations (0.0001 to 0.01 mol⋅L⁻¹) as a function of time were conducted on the solubility of 2-line ferrihydrite (Fe(OH)₃(s)), PuO₂(am) in the presence of different concentrations of Ca ions, and mixtures of PuO₂(am) and Fe(OH)₃(s). The solubility data were interpreted using Pitzer’s ion-interaction approach to determine/validate the solubility product of Fe(OH)₃(s), the complexation constants of Pu(IV)-EDTA and Fe(III)-EDTA, and to determine the effect of EDTA in solubilizing Pu(IV) from PuO₂(am) in the presence of Fe(III) compounds and aqueous Ca concentrations. Predictions based on these extensive fundamental data show that environmental mobility of Pu as a result of Pu(IV)-EDTA complexation as reported/implied in the literature is a myth rather than the reality. The data also show that in geologic environments where Pu(III) and Pu(V) are stable, the EDTA complexes of these oxidation states may play an important role in Pu mobility.     

Sulfur-containing polymers by the reaction of diphenyl sulfide with sulfur chlorides

The electrophilic reaction of sulfur dichloride with diphenyl sulfide proceeds efficiently at room temperature to yield oligo(phenylene sulfide) in the presence of a catalytic amount of Fe powder. Sulfur dichloride shows higher reactivity than sulfur monochloride. The reaction is promoted through the activation of sulfur dichloride by Fe powder. The polymeric product contains a linear structure linked by disulfide and sulfide bonds.     

Indirect Spectrophotometric Method for Determination of Sulfur Dioxide

Abstract

An operationally inexpensive and satisfactory analytical procedure for sulfur dioxide is proposed. The reagent 3-methyl-1,2-cyclopentanodione dithiosemicarbazone has been used to determine trace amounts of sulfur dioxide indirectly using the reduction of Fe(III) to Fe(II) principle. In order to find the optimal conditions for SO₂ determination, properties of 3-Me-CPDT-Fe(II) complex such as its composition, stability and free energy change of formation have been determined. The best conditions for the complex formation such as standing time, pH, wavelength and the effect of interfering ions are described. The complex has been used with success in spectrophotometric determination of SO₂. The procedure can determine down to 0.63 μg and recoveries are better than 97.5%. The method is also suitable for determination of sulfur dioxide in the air provided that interfering gases such as H₂S and NO₂ are removed.     

Structural and spectral studies of an iron(III) complex [Fe(Pranthas)2][FeCl4] derived from 2-acetylpyridine-N(4), N(4)-(butane-1, 4-diyl) thiosemicarbazone (HPranthas)

A novel iron(III) complex of 2-acetylpyridine N(4), N(4)-(butyl-1, 4-diyl) thiosemicarbazone (HPranthas), [Fe(Pranthas)₂]FeCl₄ was synthesized and physico-chemically characterized by means of partial elemental analysis, magnetic measurements (polycrystalline state), UV-Vis and IR spectroscopies. The presence of spin-paired iron(III) cation with ground state is revealed by the EPR and Mössbauer spectral data. Structure of the free ligand HPranthas and the complex [Fe(Pranthas)₂]FeCl₄ were solved by single crystal X-ray diffraction. The framework of iron(III) complex consists of a discrete monomeric cationic entity containing low spin iron(III) in a slightly distorted octahedral environment. The metal ion is bonded to one sulfur and two nitrogens of each thiosemicarbazone molecule. The tetrachloroferrate(III) ion acts as counterion.     

A Molecular Low-Coordinate [Fe-S-Fe] Unit in Three Oxidation States

A [Fe-S-Fe] subunit with a single sulfide bridging two low-coordinate iron ions is the supposed active site of the iron-molybdenum co-factor (FeMoco) of nitrogenase. Here we report a dinuclear monosulfido bridged diiron(II) complex with a similar complex geometry that can be oxidized stepwise to diiron(II/III) and diiron(III/III) complexes while retaining the [Fe-S-Fe] core. The series of complexes has been characterized crystallographically, and electronic structures have been studied using, inter alia, ⁵⁷Fe Mössbauer spectroscopy and SQUID magnetometry. Further, cleavage of the [Fe-S-Fe] unit by CS₂ is presented.     

Rapid Synthesis of Size-controlled Gold Nanoparticles by Complex Intramolecular Photoreduction

A rapid synthesis of size-controlled gold nanoparticles was proposed.The method is based on the sensitive intramolecular photoreduction reaction of Fe(Ⅲ)-EDTA complex in chloroacetic acid-sodium acetate buffer solution,where Fe(Ⅱ)-EDTA complex generated by photo-promotion acts as a reductant of AuCl-4 ions.Gold nanoparticles formed were stabilized by EDTA ligand or other protective agents added.As a result,well-dispersed gold nanoparticles with an average diameter range of 6.7 to 50.9 nm were obtained.According to the characterizations by the UV spectrum and TEM,the intramolecular charge transfer of the excited states of complex Fe(Ⅲ)-EDTA and the mechanism of forming gold nanoparticles were discussed in detail.     

A dinuclear oxygen-bridged Schiff base iron(III) complex derived from <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-bis(4-methoxy-2-hydroxybenzylidene)-2,2-dimethylpropane-1,3-diamine

The μ-oxo-bridged Fe(III) dimer complex [{Fe(4-MeOL1)}₂(μ-O)]?HOCH₃, (H₂-4-MeOL1 = N,N′-bis(4-methoxy-2-hydroxybenzylidene)-2,2-dimethylpropane-1,3-diamine), 1 is synthesized and characterized by single crystal X-ray diffraction. Complex 1 contains a [{Fe(4-MeOL1)}2(μ-O)] dimeric unit with a methanol solvent molecule of crystallization. Each Fe(III) ion has a distorted square-pyramidal coordination geometry. In the basal plane, the Fe(III) atom is coordinated by two N and two O atoms of the Schiff base ligand. The apical position is occupied by a bridging O^2– ion, linking another Fe(III) ion in the complex. There are intermolecular C–H…O and C–H…π interactions among the dinuclear complexes.     

Studies on the effect of non-ionic surfactant micelles on color reactions: III. The effect of micelles on metal ion reactivity in the Fe(III)-PAN-Triton X-100 system

Fe(III) and PAN form Fe(PAN),OH complex in CHCl₃ extract which shows absorption maxima at 550 nm and 775 nm (log ε₅₅₀,= 4.06, log ε₇₇₅ = 4.08). In the Fc(III)-PAN-Triton X-100 system, two complex species Fe(PAN)₂⁺ and/or Fe(PAN)₂OH may be formed. Fe(PAN)₂⁺ possesses a strongly absorbing peak at 550 nm (log ε₅₅₀ = 4.36). In this paper the effect of Triton X-100 micelles on the Fe(III)-PAN color reaction has been investigated in detail. We consider that the high density of ether linkages in Triton X-100 micelles concentrate hydrous Fe(III) ions and change their existing state. Moreover, the micelles not only raise the reactivity of Fe(III), but also enhance the rate of the color reaction.     

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.     

Kinetic study of the Ce(III)‐, Mn(II)‐ or Fe(phen)32+‐catalyzed Belousov–Zhabotinsky reaction with ethyl hydrogen malonate

In a stirred batch reaction, Fe(phen)₃²⁺ ion behaves differently from Ce(III) or Mn(II) ion in catalyzing the bromate‐driven oscillating reaction with ethyl hydrogen malonate [CH₂COOHCOOEt, ethyl hydrogen malonate (EHM)]. The effects of N₂ atmosphere, concentrations of bromate ion, EHM, metal ion catalyst, sulfuric acid, and additive (bromide ion or bromomalonic acid) on the pattern of oscillations were investigated. The kinetic study of the reaction of EHM with Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion indicates that under aerobic or anaerobic conditions the order of reactivity toward reacting with EHM is Mn(III) > Ce(IV) ≫ Fe(phen)₃³⁺, which follows the same trend as that of the malonic acid system. The presence of the ester group in EHM lowers the reactivity of the two methylene hydrogen atoms toward bromination or oxidation by Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion. No good oscillations were observed for the BrO₃₋‐CH₂(COOEt)₂ reaction catalyzed by Ce(III), Mn(II), or Fe(phen)₃²⁺ ion. A discussion of the effects of oxygen on the reactions of malonic acid and its derivatives (RCHCOOHCOOR′) with Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion is also presented. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 52–61, 2000     

Polymer immobilized Fe(III) complex of 2-phenylbenzimidazole: An efficient catalyst for photodegradation of dyes under UV/Visible light irradiation

Fe(III) complex of 2-phenylbenzimidazole has been covalently anchored on polymer and characterized by elemental analysis, FT-IR, far-IR, BET surface area measurements, UV–Vis/DRS spectroscopy, thermo-gravimetric analysis and magnetic moment measurements by VSM which confirmed an octahedral environment around Fe(III) in the bound complex. The photocatalytic performance of this complex was evaluated in the photodegradation of dyes in presence of H₂O₂ as an oxidizing agent. Suitable reaction conditions have been optimized by considering the effects of various reaction parameters such as pH, oxidants, concentration of dye, H₂O₂ and catalyst for the maximum degradation of dye. The photodegradation was found to be 100% with complete mineralization in 150?min. The comparison of photocatalytic efficiency of the catalyst under visible light, sunlight and dark conditions are accomplished. Comparison between catalytic activity of the polymer-supported complex and unbound complex demonstrated that the polymer-supported complex was more active. Photocatalytic performance of PS-Fe(III)PBMZL was also compared with commercial TiO₂ (P25). This heterogeneous complex retained its activity up to 8 runs. A tentative mechanism has been proposed.     

A new dinuclear heme-copper complex derived from functionalized protoporphyrin IX

A new biomimetic model for the heterodinuclear heme/copper center of respiratory oxidases is described. It is derived from iron(III) protoporphyrin IX by covalent attachment of a Gly-L-His-OMe residue to one propionic acid substituent and an amino-bis(benzimidazole) residue to the other propionic acid substituent of the porphyrin ring, yielding the Fe(III) complex 1, and subsequent addition of a copper(II) or copper(I) ion, according to needs. The fully oxidized Fe(III)/Cu(II) complex, 2, binds azide more strongly than 1, and likely contains azide bound as a bridging ligand between Fe(III) and Cu(II). The two metal centers also cooperate in the reaction with hydrogen peroxide, as the peroxide adducts obtained at low temperature for 1 and 2 display different optical features. Support to this interpretation comes from the investigation of the peroxidase activity of the complexes, where the activation of hydrogen peroxide has been studied through the phenol coupling reaction of p-cresol. Here the presence of Cu(II) improves the catalytic performance of complex 2 with respect to 1 at acidic pH, where the positive charge of the Cu(II) ion is useful to promote O-O bond cleavage of the iron-bound hydroperoxide, but it depresses the activity at basic pH because it can stabilize an intramolecular hydroxo bridge between Fe(III) and Cu(II). The reactivity to dioxygen of the reduced complexes has been studied at low temperature starting from the carbonyl adducts of the Fe(II) complex, 3, and Fe(II)/Cu(I) complex, 4. Also in this case the adducts derived from the Fe(II) and Fe(II)/Cu(I) complexes, that we formulate as Fe(III)-superoxo and Fe(III)/Cu(II)-peroxo exhibit slightly different spectral properties, showing that the copper center participates in a weak interaction with the dioxygen moiety.     

Kinetic study of the Ce(III)‐, Mn(II)‐ or Fe(phen)32+‐catalyzed Belousov‐Zhabotinsky reaction with 2‐ketoglutaric acid

The Belousov‐Zhabotinsky (BZ) reaction of bromate ion with 2‐ketoglutaric acid (KGA) in aqueous sulfuric acid catalyzed by Ce(III), Mn(II), or Fe(phen)₃²⁺ ion exhibits sustained barely damped oscillations under aerobic conditions. In general, the reaction oscillates without an induction period. Fe(phen)₃²⁺ ion behaves differently from Ce(III) and Mn(II) ions in catalyzing this oscillating system. The gem‐diol form of KGA exhibits different behavior from that of the keto form of KGA in the BZ reaction. The kinetics and mechanism of the reaction of KGA with Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion was investigated. The order of relative reactivities of metal ions toward reaction with KGA is Mn(III) > Ce(IV) ≫ Fe(phen)₃³⁺. Experimental results are rationalized. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 101–107, 2001