NMR and EPR investigations of iron corrolates: iron(III) corrolate pi cation radicals or iron(IV) corrolates?

The chloroiron corrolates of 2,3,7,8,12,13,17,18-octamethyl- and 7,13-dimethyl-2,3,8,12,17,18-hexaethylcorrole ([(Me8C)FeCl] and [(7,13-Me2Et6C)FeCl], respectively) and their bisimidazole complexes have been investigated by NMR spectroscopy as a function of temperature, and by EPR spectroscopy at 4.2 K. Magnetic susceptibilities were measured by the modified Evans method. It is found that the electron configuration of the chloroiron corrolates is that of a S = 3/2 Fe(III) center coupled to a corrolate pi radical, where one electron has been removed from the pi system of the corrolate. This pi radical is antiferromagnetically coupled to the unpaired electrons of the iron to yield an overall S = 1 complex, as evidenced by the very large positive shifts of the meso-H resonances (183 and 172 ppm). That this antiferromagnetic coupling is very strong is supported by the near-Curie behavior of the 1H chemical shifts. For the chloroiron corrolates in the presence of imidazole, imidazole-d4, and N-methylimidazole at temperatures of -50 degrees C and below, the mono- and bisligand complexes are formed. The NMR spectra can be assigned on the basis of chemical exchange between the chloroiron(III) parent complex and the bisligand complex at -30 degrees C, and between the bisligand complex and the monoligand complex at -50 degrees C. The bisimidazole complexes show pyrrole CH2 and CH3 resonances characteristic of low-spin Fe(III) centers (S = 1/2), but with strongly upfield-shifted meso-H resonances (delta values of -95 and -82.5 ppm for the octamethyl complex and -188 and -161 ppm for the dimethylhexaethyl complex at 203 K) characteristic of the presence of a macrocycle-centered unpaired electron. The magnetic moments of these bisligand complexes are somewhat lower than expected for overall S = 1 systems, and decrease as the temperature is lowered. The lower apparent magnetic moments (2.0-1.8 mu B between -50 and -90 degrees C) are believed to be caused by a combination of weak or no magnetic coupling between the metal and macrocycle electrons and decreasing solubility of the complex as the temperature is lowered. The non-Curie behavior of the 1H chemical shifts observed in the low-temperature (-50 to -90 degrees C) NMR spectra likely arises from a combination of the effects of weak antiferromagnetic coupling of metal and macrocycle spins, a low-lying electronic excited state, and ligand binding/loss equilibria at the highest temperatures studied (-50 degrees C).     

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.     

β-Nitro derivatives of iron corrolates

Two different methods for the regioselective nitration of different meso-triarylcorroles leading to the corresponding β-substituted nitrocorrole iron complexes have been developed. A two-step procedure affords three Fe(III) nitrosyl products-the unsubstituted corrole, the 3-nitrocorrole, and the 3,17-dinitrocorrole. In contrast, a one-pot synthetic approach drives the reaction almost exclusively to formation of the iron nitrosyl 3,17-dinitrocorrole. Electron-releasing substituents on the meso-aryl groups of the triarylcorroles induce higher yields and longer reaction times than what is observed for the synthesis of similar triarylcorroles with electron-withdrawing functionalities, and these results can be confidently attributed to the facile formation and stabilization of an intermediate iron corrole π-cation radical. Electron-withdrawing substituents on the meso-aryl groups of triarylcorrole also seem to labilize the axial nitrosyl group which, in the case of the pentafluorophenylcorrole derivative, results in the direct formation of a disubstituted iron μ-oxo dimer complex. The influence of meso-aryl substituents on the progress and products of the nitration reaction was investigated. In addition, to elucidate the most important factors which influence the redox reactivity of these different iron nitrosyl complexes, selected compounds were examined by cyclic voltammetry and thin-layer UV-visible or FTIR spectroelectrochemistry in CH(2)Cl(2).     

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.     

Preparation of iron—polysiloxane vertically ordered microneedles from a suspension of iron microparticles in liquid silicone rubber

Russian Chemical Bulletin - A simple method for the preparation of the vertically located flexible iron—polysiloxane magnetic needles up to 12 mm long by the self-organization of iron...     

Reactions of chelated η-pentadienyl iron complexes with nucleophiles

Ferracyclic (1-3-η³)pentadienyl complexes with electronically decoupled allyl and vinyl moieties were reacted with various heteroatom and carbon nucleophiles. Primary amines selectively attacked neutral (4-6-η³-pentadienyl)ferralactones 2 on the end of the allyl ligand to give 3-(endo-vinyl)-(4-6-η³-allyl)ferralactams 4 and by a similar reaction of the latter eventually 6-(exo-vinyl)-(4-6-η³-allyl)ferralactams 5. -like attack on the conjugated coplanar vinyl residue of 2 was not observed. The cationic η³-allyl complex 3 was attacked by nucleophiles either on the allylic terminus furnishing free (1Z, 3E)-dienes 8, or on the vinyl residue which is part of an activated Michael system to give η⁴-1,3-diene complexes 9. η⁴-1,3,5-Triene complex 10 was obtained with basic nucleophiles.     

Mössbauer study of Japanese ancient iron slag

Mössbauer spectroscopy was applied to an investigation of ancient iron slags, excavated at the ancient ruins for iron manufacturing in order to deduce the raw materials and operative conditions of the furnace. From the Mössbauer spectra, it was found that the slags consisted of fayalite, wüstite, ulvöspinel and magnetite.     

Mössbauer study of the effect of boron and iron contents on the dynamic behavior of iron in sodium phosphate glass system

Mössbauer measurements were performed at different temperatures in order to examine the dynamic behavior of iron in the glass system: 42.5% P₂O₅, 42.5% Na₂O, 15% Fe₂O₃. Variation of the dynamic behavior was traced by substituting B₂O₃ for P₂O₅ [30 P₂O₅, 12.5 B₂O₃, 42.5 Na₂O, 15 Fe₂O₃] and by increasing the amount of iron at the expense of Na₂O [42.5 P₂O₃, 15 Na₂O, 42.5 Fe₂O₃]. The Mössbauer measurements gave the values of Debye temperature (_D), mean square displacement <²>, mean square velocity <v ² > of oscillation, the lattice time () and the strength parameter (B) for each glass. These values were discussed with the results of DTA, density, hardness and D. C. conductivity.     

Liquid-liquid extraction of α-activation products of iron with HDEHP

The carrier-free radiotracers,^52,56Mn,^55,56,58Co and^56,57Ni were produced simultaneously by accelerated -particle activation of iron. They were subsequently studied through LLX using the liquid cation exchanger, HDEHP, as an extractant. A considerable enrichment of individual carrier free radionuclides of manganese, cobalt and nickel was achieved. Production and verification of purity of the carrier-free radiotracers at different stages of their extraction were carried out by -ray spectroscopic studies.     

Phase state of iron system colloidal catalyst in butadiene polymerization

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Fischer–Tropsch synthesis over iron catalysts with corncob-derived promoters

A sustainable strategy for Fischer–Tropsch iron catalysts is successfully achieved by embedding of synergistic promoters from a renewable resource, corncob. The iron-based catalysts, named as "corncob-driven"catalysts, are composed of iron species supported on carbon as primary active components and various minerals(K, Mg, Ca, and Si, etc.) as promoters. The corncob-driven catalysts are facilely synthesized by a one-pot hydrothermal treatment under mild conditions. The characterization results indicate that the formation of iron carbides from humboldtine is clearly enhanced and the morphology of catalyst particles tends to be more regular microspheres after adding corncob. It is observed that the optimized corncob-driven catalyst exhibits a higher conversion than without promoters' catalyst in Fischer–Tropsch synthesis(ca. 73% vs. ca. 49%). More importantly, a synergistic effect exists in multiple promoters from corncob that can enhance heavy hydrocarbons selectivity and lower CO_2 selectivity, obviously different from the catalyst with promoters from chemicals. The proposed synthesis route of corncob-driven catalysts provides new strategies for the utilization of renewable resources and elimination of environmental pollutants from chemical promoters.     

Transesterification catalyzed by iron(III) β-diketonate species

A practical and clean protocol for transesterification catalyzed by a 5 mol % cheap, non-toxic and moisture stable Fe(acac)₃ or other iron(III) β-diketonate species in solvent, such as heptane under azeotropic condition is developed. A remarkable rate enhancement was observed upon the addition of 5 mol % of an inorganic base, such as Na₂CO₃, which suggests that faster formation of a dimeric μ-alkoxy-bridged iron(III) species under alkaline conditions facilitates catalytic turnover. This system provides smooth transesterification over a wide range of structurally diverse esters and alcohols without disturbing functional groups. In addition, the use of iron β-diketonate complexes as catalysts is more environmentally friendly, safer, and economical than other transition-metal catalysts. Preliminary mechanistic studies indicate that the active catalyst is likely a dimeric μ-alkoxy-bridged iron(III) species, as determined by X-ray crystallography of [Fe(dbm)₂(O-n-Bu)]₂ derived from the alcoholysis of Fe(dbm)₃ under alkaline conditions.     

Stereocontrolled acylation of (η4-cycloheptatriene)iron tricarbonyl

The anion derived by deprotonating (cycloheptatriene)Fe(CO)₃ reacts with acid chlorides to give exo C-7 substitution. The acyl group is readily isomerized to C-5 on treatment with base. The C-7 acylated products can be deprotonated; the resulting anions react at oxygen with acyl chlorides and Me₃SiCl, and at carbon with MeI.     

Oxygen reduction on an iron–carbonized aerogel nanocomposite electrocatalyst

Iron–carbonized aerogel nanocomposite was prepared from highly porous polyacrylonitrile microcellular foams containing a salt of iron, followed by carbonization. The electrochemical reduction of oxygen at this material was studied by using the rotating disk electrode method. In common with Pt/C, iron–carbonized aerogel nanocomposite presented excellent electrocatalytic activity for the oxygen reduction under experimental conditions close to those of a fuel cell cathode, that is, at the catalyst/Nafion interface in acidic solutions.     

Minerals associated with artists’ paintings and archaeological iron objects

This article provides a short review of mineral-based pigments used in paintings with examples drawn from technical studies of selected historic paintings. Pigments such as azurite, natural ultramarine, orpiment, and clay earth pigments have been identified. Some examples will also be given of particular case studies which describe the alteration of selected pigments and consequences of these interactions. The second theme shows how use has been made of such interactions in evaluating the effects of environmental impact on paintings and reference is made to previous studies and the application of paint films as dosimeters. Accelerated ageing and site exposure studies are reported, and results provide information on pigment binder interactions. Dynamic mechanical analysis (DMA) and thermogravimetric analysis (TG) have been used to characterise the behaviour of pigments in binding media and to assist in characterising samples from wall paintings. Reference is also made to the occurrence of iron-oxide based minerals present as corrosion products in archaeological iron objects. Examples are given of objects from two archaeological sites in England, the Anglo-Saxon burial site Sutton Hoo in Suffolk, and the burial site in Wetwang, East Yorkshire. It will be shown that post excavation changes occur in the objects and this information is used to inform preventive conservation of these objects, in storage and in display.     

Redox potentials of iron—nitrosyl complexes: DFT calculations

Quantum chemical calculations of the structure and solvation energies of mono- and dianions of Roussin’s red salt esters [Fe₂(μ-RS)₂(NO)₄] (R = Me, Et, Prⁱ, Bu^t) in solutions in THF and acetonitrile were carried out. In monoanions, an additional electron is localized on one Fe(NO)₂ fragment, which leads to significant structural distortion of the anion compared to neutral molecule. The second electron is localized on the other Fe(NO)₂ fragment; this causes symmetrization of the dianion geometry. There are good linear correlations between the calculated and experimental redox potentials of these systems. A relationship was proposed for estimation of the redox potentials of related iron—nitrosyl complexes. The standard redox potentials of the complex with R = Ph in water, DMSO, and acetonitrile evaluated using this expression lie between −0.5 and −0.6 V.     

Can electrospray ionization help the characterization of iron gall inks? Investigation on the interactions of gallic acid with iron ions in aqueous solutions

In the present work, an investigation has been conducted by electrospray ionization (ESI) experiments to characterize the structures of iron gall ink complexes in solution. Simple mono and polyphenolic acid molecules added to iron sulfate salts were chosen to model the recipes of ink composition. Theoretical calculations have been used (1) to determine the stability of the ionic complexes generated in the gas phase, (2) to explain which structures are more likely generated in the electrospray ion source, and (3) to determine which mechanisms are likely involved in their formation. Fragmentation pathways of the derived structures have also been investigated and rationalized to facilitate the interpretation of the data obtained under collisionally induced dissociation (CID) conditions.The present study confirms the assumption that ESI experiments with ions that are preformed in solution must be considered carefully. As a matter of fact, the study of ion formation mechanisms in the ion source is necessary to establish relationships between the ion structures in the condensed phase and the gas phase.