Synthesis and structure of mono- and dinuclear cyclopentadienyl–indenyl complexes of iron(II) and further reactions to mixed tri- and tetranuclear iron–cobalt complexes

The reaction of a mixture of sodium cyclopentadienide and the monolithium salt or dilithium salt of 2,2-bis(indenyl)propane with FeCl₂ leads to the mononuclear complex [(η⁵-C₅H₅)Fe(η⁵-ind-C(CH₃)₂-ind)] (ind = 1-indenyl) (1) and the dinuclear complex [{(η⁵-C₅H₅)Fe(η⁵-ind)}₂C(CH₃)₂] (2), respectively. [(η⁵-Me₅C₅)Fe(tmeda)Cl] reacts with dilithium 1,1′-biindenyl under formation of [{(η⁵-Me₅C₅)Fe}₂(μ-η⁵:η⁵-1,1′-biind)] (4). Due to the annelated arene rings of the η⁵-indenyl ligands, 2 and 4 may act as 4-electron donor ligands, as exemplified by the reaction with the triple-decker complex [{(η⁵-Me₅C₅)Co}₂(μ-η⁶:η⁶-toluene)], which afforded the tetranuclear dimer of triple-decker complexes [{(η⁵-C₅H₅)Fe(η⁵-Me₅C₅)Co(μ-η⁵:η⁴-1-ind)}₂C(CH₃)₂] (3) and the trinuclear complex [{(η⁵-Me₅C₅)Fe}₂(η⁵-Me₅C₅)Co(μ₃-η⁵:η⁴:η⁵-1,1′-biind)] · Et₂O (5 · Et₂O) by replacement of the central toluene deck, respectively. The [(η⁵-Me₅C₅)Co] fragments of 3 and 5 are bonded via the six-membered rings of the indenyl ligands in a η⁴-fashion. Caused by the coordination to the Co atoms the six-membered rings lose their planarity and adopt a butterfly structure. The coordination geometry of the Fe atoms is similar in all five complexes. Each Fe atom is coordinated by the C atoms of one of the five-membered rings of the indenyl ligands in a slightly distorted η⁵ manner (η³ + η²-coordination) and by a cyclopentadienyl ligand in a regular η⁵-fashion. The structures of 3 and 5 represent the first examples of slipped triple-decker complexes which comprise indenyl ligands in a μ-η⁵:η⁴ coordination mode.     

Iron–cobalt and iron–cobalt–nickel nanowires deposited by means of cyclic voltammetry and pulse-reverse electroplating

Metal nanowires composed of Fe–Co and Fe–Co–Ni alloys were successfully prepared by means of cyclic voltammetry (CV) and pulse-reverse (PR) electroplating techniques from acidic metal chloride solutions. The anodic dissolution process in the CVs or in the reverse electroplating period was found to be the key factor influencing the formation of metal nanowires. The addition of nickel into the Fe–Co alloy was found to extend the diameter of these nanowires. The morphology and crystalline information of these alloy deposits prepared by CV and PR deposition techniques were obtained from the field-emission scanning electron microscopic (FE-SEM) photographs and X-ray diffraction (XRD) patterns, respectively.     

Electrochemical synthesis and properties of iron–titanium dioxide composite coatings

Deposition of Fe/TiO₂ composite coatings from a colloidal methanesulfonate electrolyte containing titanium dioxide hydrosol was studied. The TiO₂ content in the composite increases with increasing the dispersed phase content and decreasing the current density. Incorporation of TiO₂ particles into the iron matrix resilts in an increase in the microhardness of the deposit. The electroplated Fe/TiO₂ composite coating was used as a heterogeneous photocatalyst for the decomposition of an organic dye under the action of UV radiation.     

Synthesis and structural characterization of iron–sulfur complexes with hydrophilic nitrogen–phosphorus ligands

Reaction of the parent complex (μ-PDT)Fe₂-(CO)₆ (A) (PDT = 1,3-SCH₂CH₂CH₂S^2?) with the bidentate N/P ligand [(Ph₂P)₂N(C₆H₄Cl-p)] in the presence of Me₃NO as decarbonylating agent produced an unexpected iron–sulfur complex [(μ-PDT)Fe₂(CO)₅{PPh₂(NHC₆H₄Cl-1,4)}] (1). Extending this chemistry further, two similar complexes [(μ-PDT)Fe₂(CO)₅{PPh₂(NHC₆H₄NO₂-1,4)}] (2) and [(μ-PDT)Fe₂(CO)₅{PPh₂(NHC₆H₄CO₂Et-1,4)}] (3) could be prepared from the simple substitution reactions of the precursor A with the monodentate N/P ligands Ph₂P(NHC₆H₄NO₂-1,4) and Ph₂P(NHC₆H₄CO₂Et-1,4), respectively. These new complexes, which can be considered as active site models of [FeFe] hydrogenases, have been characterized by elemental analysis, FTIR, and NMR (¹H, ¹³C, ³¹P) spectroscopies, as well as by X-ray crystallography for complex 1.     

Binuclear cyanide-bridged cobalt–iron complexes

Three new binuclear complexes: [(NO)(CN)₄FeCN–Co(en)₂] · H₂O (1), [(NO)(CN)₄FeCN–Co(pn)₂] · 2H₂O (2), and [(NO)(CN)₄FeCN–Co(tn)₂] · 3H₂O (3) (en = ethylenediamine, pn = 1,2-diaminopropane; tn = 1,3-diaminopropane) have been prepared and their properties studies by i.r., u.v. spectroscopy, cyclic voltammetry, and by magnetic measurements.     

Electrochemical performance and large positive–negative magnetodielectric coupling in iron chromite spinels

Spinel ferrites with remarkable electrochemical performance and magnetodielectric (MD) coupling are promising candidates for energy storage and spintronic devices. This study focuses on structural phases, dielectric and magnetic polarization along with magnetodielectric (MD) coupling and electrochemical response of Fe-Cr spinels. Low cost sol–gel method is used to synthesize iron chromite nanopowders. Iron to chromium (Fe/Cr) ratio is varied in the range of 0.2–0.65 (with interval of 0.05). XRD patterns confirm the formation of phase pure FeCr₂O₄ at Fe/Cr ratios of 0.45, 0.6 & 0.65. Amorphous behavior is observed at Fe/Cr ratios of 0.2, 0.25, 0.5 & 0.55. Mixed phases are observed at 0.3, 0.35 & 0.4 Fe/Cr ratios. Formation of pure spinel phase at Fe/Cr ratio of 0.45 results in high saturation magnetization of 9.2 emu/g. High grain boundary resistance (189.62kΩ) and high dielectric constant (～83.38 at log f = 5.0) along with low tangent loss (0.00423 at log f = 5) are observed at Fe/Cr ratio of 0.45. Magneto dielectric studies confirm positive magneto dielectric constant (MDC) of synthesized nanopowders at 0.45, 0.6 & 0.65 Fe/Cr ratios. Cyclic voltammetry is performed at constant potential window. Oxidation/reduction process leads to the pseudo-capacitive response of the material. The cyclic voltammetry curves show specific capacitance of 156 Fg^?1, 144 Fg^?1 and 152 Fg^?1 at scan rate of 25 mV/s at Fe/Cr ratios of 0.45, 0.6 & 0.65 of FeCr₂O₄ nanopowders, respectively. The galvanostatic charging/discharging behavior shows capacitive behavior of FeCr₂O₄ nanopowders. The electrochemical results suggest that synthesized nanopowders have potential for energy storage system.     

Freeze-drying assisted sol–gel-derived silica-based particles embedding iron: synthesis and characterization

New silica-based particles embedding iron were synthesized following a freeze-drying-assisted sol–gel route. The samples were preliminary characterized in view of potential applications as theranostic magnetic resonance imaging (MRI) contrast agents and for hyperthermia treatment. The structural changes induced by iron addition were studied by X-ray diffraction, Fourier transform infrared and electron paramagnetic resonance spectroscopies. The addition of Fe₂O₃ impedes the SiO₂ crystallization denoting that iron plays, in this case, the role of a glass network stabilizer. The composition on surface and nearby was analyzed by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy both before and after samples immersion in simulated body fluid. The results suggest the nominal composition with 5?mol% Fe₂O₃ added to 0.7SiO₂?0.3Na₂O matrix of interest for further investigations as potential MRI contrast agent and hyperthermia vector.

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Geometry,electronic structure,and magnetic ordering of iron–carbon nanoparticles

The geometry optimization of Fe _n C _m and Fe _n C _m ⁺ nanoparticles from FeC₄ to Fe₇C₈ was carried out using DMol³ method. The most stable isomers for neutral and charged clusters are found with the use of ‘binomial’ scheme. For each investigated composition, the value of binding energy per atom for the ground isomer was evaluated as well as the number of configurations with binding energies which are close to that of the ground geometry. In almost all compositions, the isomers with ferromagnetic ordering of spins on Fe atoms are found to have the greater dissociation energy than those with any other spin ordering.     

Preparation and characterization of supported bimetallic gold–iron nanoparticles,and its potential for heterogeneous catalysis

Research on Chemical Intermediates - Bimetallic gold–iron catalysts supported on ZrO2 and TiO2 were prepared by under potential deposition. The characterization of the catalysts was performed...     

Core–shell-structured silica-coated magnetic carbonyl iron microbead and its magnetorheology with anti-acidic characteristics

We synthesized silica-coated soft magnetic carbonyl iron (CI) particles through a modified Stöber method, in which the CI particles were pretreated with a grafting agent to enhance the affinity of a precursor of silica. Synthesized magnetic microbeads were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and anti-acid test in HCl solution. Silica-coated CI shows not only improved wettability to silicone oil with a lower off-state shear viscosity as a better magnetorheological fluid under an applied magnetic field but also enhanced anti-acidic property.     

Synthetic and structural studies of dicobalt–iron complexes with intramolecular bridging bidentate ligands

Treatment of (μ₃-S)FeCo₂(CO)₉ (1) with diphenyl-2-pyridylphosphine (2-C₅H₄NPPh₂) or Ph₂PN(CH₂CHMe₂)PPh₂ at reflux in toluene resulted in the formation of dicobalt–iron complexes (μ₃-S)FeCo₂(CO)₇(2-C₅H₄NPPh₂) (2) and (μ₃-S)FeCo₂(CO)₇[Ph₂PN(CH₂CHMe₂)PPh₂] (3) with bridging bidentate ligands via carbonyl substitution in 51 and 53% yields, respectively. The new complexes 2 and 3 were structurally characterized by elemental analysis, IR and NMR spectroscopy, and X-ray crystallography.     

Selective oxidation of aromatic hydrocarbons by potassium and phosphorous-modified iron oxide–silica nanocomposite

Abstract  

Supported iron catalysts are active for hydrocarbon oxidation with H₂O₂, but the hydrogen peroxide dismutation is a shortcoming that may constrain their applications. Herein, we attempted to address this problem using potassium and phosphate-doped iron oxide–silica nanocomposite (KPFeSi) synthesized via sol–gel methods. The promoted silica–iron oxide nanocomposite has been characterized by elemental analyses, FTIR, X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) surface-size determination. The synthesized KPFeSi was an active catalyst in the low-temperature liquid phase oxidation of various alkyl aromatics with hydrogen peroxide in conversions of 31–78%. Furthermore, the direct oxidation of benzene into phenol using hydrogen peroxide has been achieved in the absence of any acid with this KPFeSi compound.     

Sol–gel synthesis of iron oxide–silica composite microstructures

Spherical silica particles doped with iron oxide have been synthesized via base-catalyzed one-pot sol?Cgel process using tetraethoxysilane (TEOS) and iron(III) ethoxide (ITE) as co-precursors. In the modified St?ber process adopted, depending on the concentration of ITE in the starting composition, materials of various morphologies were observed under a scanning electron microscope and an atomic force microscope. The presence of ITE significantly affected the formation process of particulate silica; the spherical particles were formed accompanied by the co-presence of irregular-shaped finer aggregates. The fraction of the aggregates with rough surfaces increased with an increase of the ITE content in the reaction mixture. Both the spherical particles and irregular-shaped aggregates contained iron hydroxide and they exhibited paramagnetic behavior. The chemical composition and physicochemical properties of the materials were determined using various complementary spectroscopic methods.     

Electrodeposition of iron–molybdenum–tungsten coatings from citrate electrolytes

Specific features of the electrodeposition of iron–molybdenum–tungsten coatings from citrate electrolytes based on iron(III) sulfate in the dc mode and with a unipolar pulsed current were studied. It was shown that varying the relative concentrations of salts of alloy-forming metals and the solution pH makes it possible to obtain lustrous compact coatings with low porosity and various contents of high-melting components. The effect of temperature on the coating composition and current efficiency was examined. The current density ranges providing high electrolysis efficiency were found and it was demonstrated that using a pulsed current favors formation of more compositionally homogeneous surface layers at a smaller amount of adsorbed nonmetallic impurities in the coatings. The iron–molybdenum–tungsten coatings are X-ray-amorphous and have better physicomechanical properties and corrosion resistance as compared with the base, which makes it possible to recommend these coatings for application in techniques for surface reinforcement and restoration of worn-out articles.     

Electrodeposition and characterization of zinc–nickel–iron alloy from sulfate bath: influence of plating bath temperature

The electrodeposition of ternary zinc–nickel–iron alloy was studied in acidic sulfate bath. The comparison between Zn, Ni, and Fe deposition and Zn–Ni and Zn–Ni–Fe co-deposition revealed that the remarkable inhibition of Ni and Fe deposition takes place due to the presence of Zn²⁺ in the plating bath. The increase in corrosion resistance of ternary deposits is not only attributed to the formation of γ-Ni₂Zn₁₁ phase but also to iron co-deposition and formation of iron phase. It was also found that the bath temperature has a great effect on the surface appearance and the deposit composition. The investigation was carried out using cyclic voltammetry and galvanostatic techniques for electrodeposition, while linear polarization resistance and anodic linear sweeping voltammetry techniques were used for corrosion study. Morphology and chemical composition of the deposits were characterized by means of scanning electron microscopy and atomic absorption spectroscopy.     

Enantioselective water-soluble iron–porphyrin-catalyzed epoxidation with aqueous hydrogen peroxide and hydroxylation with iodobenzene diacetate

The asymmetric epoxidation of styrene derivatives by H₂O₂ (or UHP) to give optically active epoxides (ee up to 81%) and hydroxylation of alkanes to give optically active secondary alcohols (ee up to 78%) were carried out in methanol and water using chiral water-soluble iron porphyrins as catalysts.     

Novel structural behaviour of iron in alkali–alkaline-earth–silica glasses

The combined effect of alkali and alkaline-earth ions on the redox, distribution, co-ordination and environment of Fe ions in alkali–alkaline-earth–silica glasses has been studied using a multi-technique approach. Wet chemical analysis and Mössbauer, electron spin resonance (ESR), optical absorption and photoluminescence spectroscopies were utilised. Behaviour generally falls into two categories, which we have termed ‘collective’ and ‘selective’. Collective behaviour occurs when alkali and alkaline-earth ions have similar effects on a property and the overall effect is cumulative. This is characterised by a linear relationship with optical basicity of the glass. Some parameters associated with the environment of Fe²⁺ ions fall into this category. Selective behaviour occurs when alkali and alkaline-earth ions have opposing effects on a property, suggesting competition or selectivity. This is characterised by a linear relationship with the alkali/alkaline-earth ionic radius ratio, cation field-strength ratio or oxide-basicity ratio. The Fe²⁺/ΣFe ratio and several parameters associated with the distribution, coordination and environment of Fe³⁺ ions fall into this category. These results have implications for the local structure surrounding Fe species. A relationship has been suggested linking coordination and distribution of Fe³⁺ ions.     

Solid-state electrochemical,X-ray and spectroscopic characterization of substitutional solid solutions of iron–copper hexacyanoferrates

Copper and iron hexacyanoferrate form a continuous series of substitutional solid solutions, which have been studied by solid-state electrochemistry, X-ray powder diffraction, IR and ESR spectroscopy. All methods unambiguously prove the formation of solid solutions. The results show the different capabilities of these techniques to study such systems. Especially in the case of poor crystallinity and strongly magnetically interacting metal ions, voltammetry of immobilized microparticles offers a powerful tool for the determination of the composition and properties of solid solutions.     

Effect of the structural change of an iron–iron oxide mixture on the decomposition of trichloroethylene

The effect of the structure of a mixture of industrially produced iron and iron oxide on the decomposition of trichloroethylene (TCE) was investigated by gas chromatography, scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray analysis, X-ray diffractometry, and ⁵⁷Fe-Mössbauer spectroscopy. The concentration of 10 mg L^?1 TCE aqueous solution decreased to 0.41, 0.52, 0.26, and 0.09 mg L^?1 when stirred for 7 days with iron–iron oxide mixtures having mass ratios of 2:8, 3:7, 4:6, and 5:5, respectively. The Mössbauer spectra of the mixtures after leaching were composed of two sextets with respective isomer shifts (δ) and internal magnetic fields (H) of 0.29_±0.01 mm s^?1 and 48.8_±0.1 T, and 0.64_±0.01 mm s^?1 and 45.5_±0.1 T, attributed to the Fe³⁺ species in tetrahedral (T _d) and the Fe²⁺ and Fe³⁺ mixed species (Fe^2.5+) in octahedral (O _h) sites, respectively. Mössbauer spectra of a 3:7 mass ratio iron–iron oxide mixture showed a gradual decrease in the absorption area (A) of zero valent iron (Fe⁰) from 40.6. to 12.6, 13.2, 3.8 2.8, and 1.0_±0.5 % and an increase in A of Fe₃O₄ from 31.8 to 59.4, 71.4, 93.2, 95.6, and 98.0_±0.5 % after leaching with 10 mg L^?1 TCE aqueous solution for 1, 2, 3, 7, and 10 days, respectively. Consistent values of the first-order rate constant were calculated as 0.32 day^?1 for Fe⁰ oxidation, 0.34 day^?1 for Fe₃O₄ production, and 0.30 day^?1 for TCE decomposition, which indicates that the oxidation of Fe⁰ was the rate-controlling factor for Fe₃O₄ production and TCE decomposition. It is concluded from the experimental results that an iron–iron oxide mixture is very effective for the decomposition of TCE.