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Proportional gas counters are commonly used in the 57Fe Mossbauer spectroscopy for their good energy resolution and insensitivity to magnetic field. However, their counting rate is usually limited by relatively long dead time. This paper demonstrates a detection performance improving technique by registration Kα escape peaks coupled together with main full energy peaks. The validity of using both peaks was verified by transmission and conversion X-rays Mossbauer spectra recording, while using proportional gas counters filled with pure krypton and a mixture of argon and methane. The influence of this method on the resulted α-Fe Mossbauer spectra was studied in a view of resonance effect, energy resolution, spectra baseline, and statistical quality. The presented technique showed that the counting rate of Mossbauer spectra accumulation was increased by 95% while using pure krypton, whereas by using a mixture of argon and methane, the counting rate reached an increase of 27%.

In this work, a green self-magnetization roasting technology for producing magnetite was proposed without adding additional. The regulatory mechanisms of the main factors (siderite dosage, roasting temperature, and roasting time) on the self-magnetization roasting process were investigated. In-situ kinetic of the self-magnetization roasting process was analyzed by the infrared gas analyzer, and the phase transformation was investigated by in-situ X-ray diffraction and Mossbauer. Under the optimal roasting conditions of 30% siderite dosage, 730 °C, and 7.5 min, the iron concentrate with Fe grade 68.82% and Fe recovery 99.48% was obtained. The kinetic and phase transformation results indicated that the self-magnetization roasting process was divided into two stages: siderite pyrolysis in the prophase stage, and hematite reduced to magnetite by reductant (FeO and CO) from siderite pyrolysis in the anaphase stage. The SEM analyses showed that the newborn magnetite crystals were mainly coarse-grained and needles, which fitted the kinetics characteristics for the Nucleation model. Using self-magnetization roasting technology, siderite and hematite would promote mutual reduction to improve product magnetism and roasting efficiency without adding reductant. Also, self-magnetization roasting will enhance the utilization rate of siderite, and it contributes to energy conservation and CO2 emission reduction.

Metal–ligand cooperation is an important aspect in earth-abundant metal catalysis. Utilizing ligands as electron reservoirs to supplement the redox chemistry of the metal has resulted in many new exciting discoveries. Here, we demonstrate that iron bipyridine-diimine (BDI) complexes exhibit an extensive electron-transfer series that spans a total of five oxidation states, ranging from the trication [Fe(BDI)]3+ to the monoanion [Fe(BDI]−1. Structural characterization by X-ray crystallography revealed the multifaceted redox noninnocence of the BDI ligand, while spectroscopic (e.g., 57Fe Mössbauer and EPR spectroscopy) and computational studies were employed to elucidate the electronic structure of the isolated complexes, which are further discussed in this report., In this study, the multifaceted electrochemistry of a bis(imino)bipyridine iron(II) complex is described. Spectroscopic studies demonstrate that throughout the various reduction processes, the oxidation state on the metal center remains constant (Fe(II); S = 1), whereas the ligand accesses four distinct oxidation states: [BDI]0 ⇄ [BDI]3−. The observed redox noninnocence of the ligand was investigated by computational methods, which is further discussed in this report.

Cobalt ferrite nanoparticles were obtained by the green synthesis method using extracts of grape peel and grape pulp. The obtained samples have been investigated by means of X-ray diffraction (XRD) analysis, scanning electron microscope (SEM), and Mossbauer spectroscopy. All samples contain pure CoFe2O4 with the cubic spinel structure of the space group Fd3m. XRD analysis indicates that cobalt ferrite nanoparticles synthesized using grape peel extract and grape pulp extract have crystallite sizes of ~ 5 and ~ 25 nm, respectively. Cation distribution and crystalline structure parameters of the samples were calculated on the basis of Mossbauer spectroscopy data. After annealing, the CoFe2O4 sample obtained with grape pulp extract has a higher degree of inversion than that obtained with grape peel extract. The decrease in the degree of inversion is related to a decrease in the average size of crystallites. The CoFe2O4 sample synthesized using grape peel extract is a more active catalyst for the decomposition of hydrogen peroxide. The first-order rate constants are 1.11·10−4 s−1 and 3.43·10−4 s−1 for the CoFe2O4-pulp and CoFe2O4-peel samples, respectively. A 100 mM H2O2 solution was decomposed to 97.4%. The surface morphology of the cobalt ferrites remains unchanged after the catalytic decomposition of H2O2. The synthesized cobalt ferrites can be used in Fenton processes as stable magnetic catalysts.

The thermal decomposition of PbC2O4-FeC2O4.2H2O mixture (1:2 mole ratio) in air, prepared using impregnation method, aiming at the production of mixed oxides; PbO-Fe2O3 (1:1 mole ratio) system have been followed using differential thermal analysis-thermogravimetry (DTA-TG). The decomposition products as well as the phases` transformations up to the ferrites production were characterized using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Mossbauer spectroscopic techniques. DTA-TG showed the formation of mixed oxides at 400oC through three well-defined steps due to dehydration and oxalates` decomposition step. XRD, FT-IR and Mossbauer measurements at different calcination temperatures indicated the formation of paramagnetic fine grained Fe2O3 particles at early decomposition stages up to 250oC followed by their transformation into magnetically ordered one by increasing calcination to 400oC. The precursor calcined at 650oC showed the initiation of PbFe4O7 ferrite formation besides the presence of unreacted PbO and Fe2O3 oxides. At 750oC, only PbFe4O7 and PbFe2O5 ferrites can be detected. Kinetic analysis of TG steps using different computational methods, in the view of different solid-state reaction kinetic models, revealed the occurrence of the decomposition up to PbO-Fe2O3 through the random nucleation growth mechanism (A2). The activation parameters calculation indicated that the fine grained Fe2O3 particles formed at early stages increasing the interfaces between lead oxalate grains and thus facilitating the decomposition.

The hexadecafluorophthalocyanine-iron complex FePcF16 was recently shown to convert olefins into ketones in the presence of stoichiometric amounts of triethylsilane in ethanol at room temperature under an oxygen atmosphere. Herein, we describe an extensive mechanistic investigation for the conversion of 2-vinylnaphthalene into 2-acetylnaphthalene as model reaction. A variety of studies including deuterium- and 18 O2 -labeling experiments, ESI-MS, and 57 Fe Mossbauer spectroscopy were performed to identify the intermediates involved in the catalytic cycle of the oxidation process. Finally, a detailed and well-supported reaction mechanism for the FePcF16 -catalyzed Wacker-type oxidation is proposed.

Carbonyl and iminyl based radical anions are reactive intermediates in a variety of transformations in organic synthesis. Herein, the isolation of ketyl, and more importantly unprecedented ketiminyl and aldiminyl radical anions coordinated to cobalt and iron complexes is presented. Insights into the electronic structure of these unusual metal bound radical anions is provided by X-Ray diffraction analysis, NMR, IR, UV/Vis and Mössbauer spectroscopy, solid and solution state magnetometry, as well as a by a detailed computational analysis. The metal bound radical anions are very reactive and facilitate the activation of intra- and intermolecular C-H bonds.

Iron (Fe) phases are tightly linked to the preservation rather than the loss of organic carbon (OC) in soil; however, during redox fluctuations, OC may be lost due to Fe phase-mediated abiotic processes. This study examined the role of Fe phases in driving hydroxyl radical (•OH) formation and OC transformation during redox cycles in paddy soils. Chemical probes, sequential extraction, and Mossbauer analyses showed that the active Fe species, such as exchangeable and surface-bound Fe and Fe in low-crystalline minerals (e.g., green rust-like Fe phases), predominantly regulated •OH formation during redox cycles. The •OH oxidation strongly induced the oxidative transformation of OC, which accounted for 15.1-30.8% of CO2 production during oxygenation. Microbial processes contributed 7.3-12.1% of CO2 production, as estimated by chemical quenching and γ-irradiation experiments. After five redox cycles, 30.1-71.9% of the OC associated with active Fe species was released, whereas 5.2-7.1% was stabilized by high-crystalline Fe phases due to the irreversible transformation of these active Fe species during redox cycles. Collectively, our findings might unveil the under-appreciated role of active Fe phases in driving more loss than conservation of OC in soil redox fluctuation events.

The chemical and mineral compositions of bauxite recovered from the Severoonezhsk Bauxite Mine (Arkhangelsk region, Russia) were studied by XRD, ICP-OES, TG/DSC, SEM, TEM, and Mössbauer spectroscopy. The iron-containing minerals of the bauxites were found to comprise alumogoethite (α-Fe1–xAlxOOH), alumohematite (α-(Fe1–xAlx)2O3), alumoakaganeite (β-Fe1–xAlxO(OH,Cl)), and chromite (FeCr2O4). The efficiency of Fe extraction from the bauxite by HCl leaching was 82.5% at 100 °C, HCl concentration of 10%, solid/liquid ratio of 1:10, and the process duration of 60 min, with aluminum loss from the bauxites below 4.5% of the total Al contents in the bauxite. Analysis of the kinetics of the iron leaching process proved diffusion to be the limiting stage of the process at 90–100 °C. Bauxite residue after leaching presented traces of α-Fe1–xAlxOOH and β-Fe1–xAlxO(OH,Cl), and most of the iron content was in the FeCr2O4. In bauxite residue after HCl leaching, in addition to iron oxide, the contents of chromium and calcium oxides significantly decreased. The iron chloride liquor after leaching contained the rare earth elements (REE) of 6.8 mg/L Sc, 4.1 mg/L Ce and 2.3 mg/L Ga. © 2021 The Nonferrous Metals Society of China. This research was funded by a Ministry of Science and Higher Education of the Russian Federation (scientific topic No. 0137-2019-0023). The authors would like to appreciate the assists from The Center for Collective Use Testing Analytical Center of the JSC “Scientific-Research Institute of Chemical Technology” and personally to Natalya Ognevskaya for chemical analysis of solid and liquid samples.

This study is focused on a simple and fast synthesis of nonstoichiometric magnetite nanoparticles with the chemical formula Fe3−XO4 and magnesium ferrite nanoparticles (Mg1−XFe2+XO4). The nanoparticles were prepared with Fe2+ ions (FeSO4 · H2O) alkalised by KOH under oxidative conditions and in a microwave field. X-ray powder diffraction (XRD) and 57Fe transmission Mössbauer spectroscopy were used to determine the phase composition and crystal structure in detail. The presence of synthetic magnetite, maghemite, goethite, and magnesium ferrite was observed. Room temperature Mössbauer spectroscopy revealed the existence of ferromagnetic sublattices and superparamagnetic fraction. The superparamagnetic component corresponds to magnesium ferrite nanoparticles. Low temperature Mössbauer spectroscopy was used to locate the blocking temperature of superparamagnetic nanoparticles and to separate the sublattices. The presumed spherical morphology of nanoparticles and their size under 100 nm have been confirmed by transmission electron microscopy (TEM). The obtained results were used to provide possible reaction scheme, which serves to tailor the synthesis to a desired application.

The facile synthesis of the first bis‐N‐heterocyclic imine‐stabilized chlorosilyliumylidene 1 is reported. Remarkably, consecutive reaction of 1 with PPh3AuCl and K2Fe(CO)4 gives rise to the unique heterobimetallic complex 1,2‐(MesNHI)2‐C2H4‐ClSiAuFe(CO)4 (4). The overall neutral complex 4 bears an unusual linear Si−Au−Fe structure and a rare anagostic interaction between the d 10‐configured gold atom and a CH bond of the mesityl ligand. According to the computational analysis and 57Fe Mössbauer spectroscopy, the formal Fe‐oxidation state remains at −II. Thus, the electronic structure of 4 is best described as an overall neutral—yet zwitterionic—heterobimetallic “Si(II)+‐Au(I)+‐Fe(‐II)2−”‐silyliumylidene complex, derived from double anion exchange. The computational analysis indicates strong hyperconjugative back donation from the gold(I) atom to the silyliumylidene ligand., The selective synthesis of a silyliumylidene‐stabilized mononuclear Au−Fe complex, by a convenient one‐pot reaction starting from bis‐NHI silyliumylidene chloride, is reported. X‐ray crystallography, IR and 57Fe Mössbauer spectroscopy, as well as computations suggest a zwitterionic Si(II)+−Au(I)+−Fe(‐II)2− bonding motif with rare anagostic CH⋅⋅⋅Au contacts and considerable backbonding capabilities of the silyliumylidene.

The [4Fe-4S] cluster containing scaffold complex HypCD is the central construction site for the assembly of the [Fe](CN)2CO cofactor precursor of [NiFe]-hydrogenase. While the importance of the HypCD complex is well established, not much is known about the mechanism by which the CN– and CO ligands are transferred and attached to the iron ion. We developed an efficient protocol for the production and isolation of the functional HypCD complex that facilitated detailed spectroscopic investigations. The results obtained by UV/Vis-, electron paramagnetic Resonance (EPR)-, Resonance Raman-, Fourier-transform infrared (FTIR), and Mössbauer spectroscopy provide comprehensive evidence for an electron inventory fit to drive multi-electron redox reactions. We demonstrate the redox activity of the HypCD complex reporting the interconversion of the [4Fe-4S]2+/+ couple. Additionally, we observed a reversible redox conversion between the [4Fe-4S]2+ and a [3Fe-4S]+ cluster. MicroScale thermophoresis indicated preferable binding between the HypCD complex and its interaction partner HypEF under reducing conditions. Together, these results suggest a redox cascade involving the [4Fe-4S] cluster and a conserved disulfide bond of HypD that may facilitate the synthesis of the [Fe](CN)2CO cofactor precursor on the HypCD scaffold complex.

This review paper summarizes early Mossbauer and DTA studies of different oxide glasses containing small amounts of iron (III) or tin (IV) as the probe. A lot of valuable information of the atomic level has been obtained about the role of nonbridging oxygen (NBO), network former (NWF), network modifier (NWM), local network structure, glass transition, structural relaxation, crystallization, etc. Introduction of alkali oxide into iron (III)-containing oxide glass causes a marked decrease in glass transition temperature (Tg) amounting to 100 °C and a concordant decrease in quadrupole splitting (Δ) of FeIII, which reflects decreased distortion of NWF–oxygen polyhedra and formation of NBO. By contrast, introduction of non-alkali oxide into oxide glass causes an increase in Tg amounting to more than 100 °C and a concordant increase in Δ, reflecting increased distortion of NWF–oxygen polyhedra in highly cross-linked network. These experimental results led to a discovery of “Tg-Δ rule”, which was consistent with the “conformer model” proposed for polymers by Matsuoka and Quan. Debye temperatures (θD) obtained by low-temperature Mossbauer measurements proved to be useful to determine short- and long-range structures of glass and glass ceramics. Isothermal annealing of vanadate glasses at temperatures higher than Tg or crystallization temperature (Tc) causes a “tunable” decrease in DC-resistivity from the order of MΩ cm to Ω cm. Introduction of metal oxide with a narrow bandgap (Eg) is highly effective to increase the conductivity after the annealing. It was proved that “structural relaxation” of NWF–oxygen polyhedra and resultant decrease in the activation energy (Ea) for conduction are responsible for the improved conductivity. Heat treatment of IR-transmitting aluminate, gallate, and tellurite glasses at temperatures higher than Tg or Tc revealed that crystallization was triggered by the cleavage of NWF–oxygen bonds. These findings will contribute to the development of functional glass and glass ceramics such as smart glass and eco-friendly glass.

The results of a Mossbauer study of amorphous CuI–AgI–As2Se3 and CuI–PbI2–SbI3–As2Se3 films are presented, applied from glass solutions in n-butylamine. By Mossbauer spectroscopy with the use of probes 57Fe and 129I, a correlation is established between the transformation of the rigidity and conservatism of the vitreous matrix on the content of copper and silver iodides in CuI–AgI–As2Se3 and CuI–PbI2–SbI3–As2Se3 films.

Pure and Sn-doped goethite (α-FeOOH) nanoparticles with good uniformity were synthesized by a facile precipitation method. The effects of Sn doping on the particle size and shape, structural, thermal, vibrational, optical and photocatalytic properties of prepared goethite nanoparticles were investigated. The Sn4+-for-Fe3+ substitution in the crystal structure of goethite was proved by determination of a significant unit cell expansion (the effect of larger Sn4+ ions) and a substantial reduction of the hyperfine magnetic field (the effect of magnetic dilution by non-magnetic Sn4+ ions). Sn doping induced a decrease in length and an increase in thickness of goethite nanocrystallites and nanoparticles, i.e., the change in particle shape from thin goethite nanorods to shorter and thicker Sn-doped goethite nanoellipsoids and nanocuboids. Thermal dehydroxylation of goethite was shifted to significantly higher temperatures by the Sn4+-for- Fe3+ substitution. The optical band gap of goethite nanoparticles narrowed with the increased Sn4+-for- Fe3+ substitution. The visible light photocatalytic efficiency for rhodamine B (RhB) degradation by a heterogeneous photo-Fenton process was gradually enhanced by Sn doping from 38% for pure goethite nanorods to 55% for Sn-doped nanoellipsoids and 70% for Sn-doped goethite nanocuboids.

A facile, gram-scale and sustainable approach has been established for the synthesis of single-atomic-site iron on N-doped carbon (FeSA@NC-20A) via the pyrolysis of aniline modified FeZn-ZIFs, in which the synthesis of zeolitic imidazolate frameworks (ZIFs) can be accomplished in water at room temperature, and no acid etching is required. The as-synthesized catalyst exhibits better performance on the chemoselective hydrogenation of nitroarenes with a broad substrate scope (turnover frequency (TOF) up to 1,727 h−1, 23 examples) than most of previously reported works. Based on high-angle annular dark field scanning transmission microscopy (HAADF-STEM) images in combination with X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), electron spin resonance (ESR), and Mossbauer spectroscopy, Fe is dispersed as single atoms via forming FeNx (x = 4–6). This work not only determines the active sites of FeSA@NC-20A for hydrogenation (FeN4), but also proposes tentative pathways for both N-H activation of hydrazine and the reduction of nitroarene on FeN4 site, both of which are the key steps for the hydrogenation of nitroarenes. In addition, this catalyst shows excellent stability, and no significant activity degradation is observed when recycling for 10 times or restoring in air for 2 months.

Egyptian granite was used in preparing some glass samples including different contents of sodium carbonate as a fluksing agent and to study the effect of different Na+ ions on some of their properties. The prepared glass samples have the chemical composition [100 -x granite .xNa2CO3, Where x = 11, 12, 13, 14 and 15 mol%]. The mixture of each sample was mixed well and prepared in a platinum crucible at 1430 °C for one hour, then quenched in air between two copper plates. The as prepared glass samples were investigated by XRD, FTIR, Mossbauer spectrometer, d.c. and a.c. conductivities. XRD results showed that the prepared samples have the glassy nature. FTIR results showed approximately similar de-convoluted bands. The identification of these bands revealed that the present vibration modes in these samples were Si-O-Si bending vibration, Si-O-Al stretching and Si-O-Si symmetric, Si-O− and Si-O-Si asymmetric stretching. Mossbauer results revealed that the granite spectrum showed two magnetic sites [Fe3O4 (Fe III) A site and Fe3O4 (Fe II, III) B site]. And also another two doublets represented Fe (II) and Fe (III). The glass samples spectra showed two doublets represented Fe2+ and Fe3+ (Oh). The a.c. conductivity at low temperature for the glass samples showed week temperature dependence and strong frequency dependence. At high temperature the behavior reversed. The a.c. behavior showed also that the relation of ln(σ) and 1/T of each glass sample exhibited one line with two slopes. This reflects that the electric conduction is due to ionic and electronic conduction. The behavior of the relation between Na+ content and ln(σ) showed the behavior of the extrinsic semiconductor at low temperature range where the pentavalent or trivalent ions of silicon matrix changed their electrical features producing p-type and n-type semiconductors respectively. The dielectric constant (e’) showed fixed values up to a certain temperature, then e’ started to increase gradually with inversely proportional to frequency.

The series M0.5(1+x)FexZr2−x(PO4)3 (M—Ni, Cu, Mn) with Sc2(WO4)3-related structure (SW) were prepared using Pechini technique and characterized by powder X-ray diffraction analysis, SEM, EDX, IR, and Mossbauer spectroscopy. The concentration and temperature limits of solid solution formation were determined, lattice parameters were calculated, and their dependencies on the phosphate’s composition were studied. The crystal structure of the phosphate Mn0.65Fe0.3Zr1.7(PO4)3 (x = 0.3) was refined by the Rietveld method basing on the powder X-ray diffraction data. The compound crystallizes in monoclinic symmetry (space group P21/n) with lattice parameters: a = 8.7941(12), b = 8.9379(16), c = 12.4353(21) A, β = 90.126(24)°, V = 977.49(27) A3. Thermal expansion coefficients of the ceramics Cu0.5(1+x)FexZr2−x(PO4)3 were determined. The volume expansion coefficients of the compounds vary in the range (4.4–10.8)∙10−5 K −1.

The aim of this paper is to compare the structural, morphological and electrical properties of the CuFe2O4 and CuFe2O4 / reduced graphene oxide composite. XRD and Mossbauer studies have shown that joint hydrothermal synthesis of cubic copper ferrite and reduction of graphene oxide leads to a decrease in ferrite particles from 14 to 8 nm. Based on the impedance spectroscopy data, a model of the obtained composite material has been prepared as a system consisting of contacting spinel particles covered with rGO clusters and separated by porous rGO. For CuFe2O4 / rGO composite material, the predominance of hopping charge transfer mechanisms has been shown, and the activation energies of electrical conductivity of grains and grain boundaries have been calculated.

Constructing synthetic models of the nitrogenase PN -cluster has been a long-standing synthetic challenge. Here, we report an optimal nitrogenase PN -cluster model [{(TbtS)(OEt2 )Fe4 S3 }2 (μ-STbt)2 (μ6 -S)] (2) [Tbt=2,4,6-tris{bis(trimethylsilyl)methyl}phenyl] that is the closest synthetic mimic constructed to date. Of note is that two thiolate ligands and one hexacoordinated sulfide are connecting the two Fe4 S3 incomplete cubanes similar to the native PN -cluster, which has never been achieved. Cluster 2 has been characterized by X-ray crystallography and relevant physico-chemical methods. The variable temperature magnetic moments of 2 indicate a singlet ground state (S=0). The Mossbauer spectrum of 2 exhibits two doublets with an intensity ratio of 3:1, which suggests the presence of two types of iron sites. The synthetic pathway of the cluster 2 could indicate the native PN -cluster maturation process as it has been achieved from the Fe4 S4 cubane Fe4 S4 (STbt)4 (1).

The products of the mechanochemical reduction of iron oxide with aluminum have been studied by means of X-ray diffraction analysis, infrared and Mossbauer spectroscopy. It is shown that the products of the mechanochemical reaction at a stoichiometric ratio of iron oxide and aluminum contain iron, α‑Al2O3, and a large amount of spinel (hercynite), which slightly decreases with an increase in the time of mechanical activation. According to the Mossbauer spectroscopy data, the reduction of iron oxide proceeds faster with a twofold increase in the aluminum content as compared to the stoichiometric one, and the excess aluminum reacts with the reduced iron, forming intermetallic FexAly phases mainly the monoaluminide FeAl strengthened by α-Al2O3 particles. Upon a threefold excess of the aluminum content over the stoichiometric one, the mechanochemical reduction slows down and the amount of FexAly intermetallic compounds with a higher aluminum content increases in the final products of reaction.

In article present the results of low-temperature Mossbauer studies of iron (III) oxide/hydroxide nanocomposite synthesized by the method of deposition. Based on these studies, the composition of the synthesized composite was revealed. The nanodispersed composite with a specific surface 280 m2/g is a hematite in the weakly disordered crystalline state (CSR 10 nm), and a lepidocrocite in the X-ray amorphous state (particles size 3-4 nm). The relative integral intensity of the Zeeman sextet, which corresponds to the magnetically ordered phase of hematite, is practically unchanged and is about 17%. The tendency to divide the magnetically ordered component into two sextets, which differ in quadrupole splitting QS= –0.21 mm/s and QS= 0.21 mm/s, respectively, is observed starting from a temperature of 190 K. As a result of annealing of the synthesized material at a temperature of 200°C, a slight redistribution (≈ 5%) of the content of paramagnetic and magnetically ordered components was recorded, which indicates the structural stability of the nanoparticles of the lepidocrocite γ-FeOOH phase at this temperature. Increase of annealing temperatures to 500oC leads to the predicted course of the phase transition γ-FеООH ® α-Fе2О3. The mechanism of growth of hematite crystallites during sintering due to fixation side faces of larger α-Fe2O3 phase of nanoparticles of the γ-FeOOH phase with simultaneous transformation of their crystal structure to side faces of larger α-Fe2O3 phase particles is presented.

Human anamorsin is an iron–sulfur (Fe–S)‐cluster‐binding protein acting as an electron donor in the early steps of cytosolic iron–sulfur protein biogenesis. Human anamorsin belongs to the eukaryotic CIAPIN1 protein family and contains two highly conserved cysteine‐rich motifs, each binding an Fe–S cluster. In vitro works by various groups have provided rather controversial results for the type of Fe–S clusters bound to the CIAPIN1 proteins. In order to unravel the knot on this topic, we used an in cellulo approach combining Mössbauer and EPR spectroscopies to characterize the iron–sulfur‐cluster‐bound form of human anamorsin. We found that the protein binds two [2Fe–2S] clusters at both its cysteine‐rich motifs., A combined in cellulo Mössbauer‐ and EPR‐based approach is applied to address controversial aspects of Fe–S cluster‐binding properties of human anamorsin, a protein involved in the biogenesis of cytosolic [4Fe–4S] cluster‐binding proteins. We show that human anamorsin binds two [2Fe–2S] clusters in‐cell in two highly conserved cysteine‐rich motifs typical of the eukaryotic CIAPIN1 protein family, with different electron‐spin‐relaxation properties.

Nanoparticles of nonstoichiometric magnetite obtained by controlled oxidation of carbonyl iron (α-Fe) in water are studied. The Fe : H2O mole ratio is 3 : 4, 4 : 4 and 3 : 10. The particles are synthesized in a high-power Activator 2S mill in an air atmosphere by 24-h milling. X-ray diffraction and spectrum analyses of the synthesized magnetite nanoparticles are performed. Formulas describing the crystal chemistry of the nanoparticles are derived using the data of Mossbauer spectroscopy. The magnetic properties and the microstructure of the nanoparticles are studied.

Greigite (Fe3S4) nanoparticles (NPs) were fabricated by the thermal decomposition method using two different surfactants: oleylamine (OLA) and 1-hexadecylamine (HDA). In both cases, the synthesized NPs were characterized as the Fe3S4 nanocrystals with minor inclusions of Fe9S11 phase. FT-IR spectroscopy and thermo-gravimetric analysis allow concluding about OLA or HDA shells covering magnetic core of NPs. Mossbauer spectra has revealed deviations of iron ions distribution among crystal positions from that presented in literature for pure greigite. In accordance with these deviations, the pronounce changes are observed in the magnetic circular dichroism (MCD) spectra which manifest themselves as the spectrum shift to higher energies of electromagnetic waves and redistribution of the MCD maximum intensities. These effects are associated with a change in the density of electronic states in the samples due to the redistribution of iron ions between octahedral and tetrahedral positions in nanocrystals under the influence of surfactants.

Magnetic nanoparticles (MNPs) have many uses for biomedical applications including drug delivery, magnetic resonance imaging (MRI) contrast agents, theranostics and hyperthermia. MNPs photo-thermally heated by laser light could be used to treat the typically difficult to access tumors such as glioblastomas. Due to their high magnetic saturation, monometallic iron nanoparticles would have an edge over iron oxide nanoparticles currently being investigated for hyperthermia. The goal of this study was to synthesize spherical iron nanoparticles less than 10 nm in diameter by thermal decomposition. The ability of various biocompatible coatings to protect the metallic iron nanoparticles from oxidation was investigated. Coatings studied included Brij, polyethylene glycol and iron oxide. Transmission electron microscopy and Mössbauer spectroscopy were utilized to characterize the coated and uncoated iron nanoparticles’ size and oxidation state to evaluate the effectiveness of the coatings and the procedures in which the coatings were applied. A ferrite shell was found to provide the best stabilization; however, its longer synthesis time increased particle size distribution. Polymer coatings provided biocompatibility but did not prevent oxidation.

Enantioenriched N-alkyl-imidazole-substituted pyridine dicarbene iron dialkyl complexes have been synthesized and characterized by 1H NMR and zero-field 57Fe Mossbauer spectroscopies as well as sin...

Niobia-based magnetic nanocomposites were prepared by covering magnetite nanoparticle cores (Fe3O4, MNP) with either Nb2O5 or Nb2O5-SiO2 shells using a two-step procedure. In the first step magnetite nanoparticles were prepared by the coprecipitation method. The second step involved their coverage with either Nb2O5 shells, through a precipitation method, or with Nb2O5-SiO2 shells, through a sol-gel protocol followed by precipitation in the presence of the CTAB surfactant. The obtained materials were exhaustively characterised by X-ray diffraction, Mossbauer spectroscopy, magnetic measurements, ICP-OES, DRIFT and Raman spectroscopy, and CO2 - and NH3-TPD measurements, and investigated for glucose dehydration to HMF. The catalytic performances were directly correlated to the nature of the supported niobia phases, which, in turn, has been dictated by the niobia content and the preparation route. The high selectivity to HMF was correlated with to the large pseudohexagonal niobium oxide (TT-Nb2O5) phase while the catalytic activity was directly correlated to the small nanoparticles size. A proper combination of these features led to an optimum catalytic system for the selective production of HMF through glucose dehydration. A third important feature making the developed catalyst promising is its magnetic property, ensured by the magnetite nanoparticles core. This allowed its easy separation from the reaction products.

Heme and non-heme iron in biology mediate the storage/release of NO• from S-nitrosothiols as a means to control the biological concentration of NO•. Despite their importance in many physiological processes, the mechanisms of N-S bond formation/cleavage at Fe centers have been controversial. Herein, we report the interconversion of NO• and S-nitrosothiols mediated by FeII/FeIII chloride complexes. The reaction of 2 equiv of S-nitrosothiol (Ph3CSNO) with [Cl6FeII2]2- results in facile release of NO• and formation of iron(III) halothiolate. Detailed spectroscopic studies, including in situ UV-vis, IR, and Mossbauer spectroscopy, support the interaction of the S atom with the FeII center. This is in contrast to the proposed mechanism of NO• release from the well-studied "red product" κ1-N bound S-nitrosothiol FeII complex, [(CN)5Fe(κ1-N-RSNO)]3-. Additionally, FeIII chloride can mediate NO• storage through the formation of S-nitrosothiols. Treatment of iron(III) halothiolate with 2 equiv of NO• regenerates Ph3CSNO with the FeII source trapped as the S = 3/2 {FeNO}7 species [Cl3FeNO]-, which is inert toward further coordination and activation of S-nitrosothiols. Our work demonstrates how labile iron can mediate the interconversion of NO•/thiolate and S-nitrosothiol, which has important implications toward how Nature manages the biological concentration of free NO•.

The spin-crossover (SCO) phenomenon is an active area of research. This paper describes the synthesis of an Fe-Ag Hofmann-type complex, {Fe(4-methylpyrimidine)2[Ag(CN)2]2}, which demonstrates a one-step SCO and single-layer Hofmann-type structure with Ag-N interactions and no Ag-Ag interactions, which is strikingly different from the previously synthesized complex {Fe(4-methylpyrimidine)2[Au(CN)2]2} that contains Au-Au interactions and no Au-N interactions. This difference can be explained in terms of the lack of relativistic effect in the Ag atoms and the different cooperative effects caused by their different structures. A scan-rate-dependent hysteresis is observed using magnetic measurement whereas not using 57Fe Mossbauer spectroscopy, suggesting that the spin transition is relatively slow.

Mononitrosyl and dinitrosyl iron species, such as {FeNO}7, {FeNO}8 and {Fe(NO)2}9, have been proposed to play pivotal roles in the nitrosylation processes of nonheme iron centers in biological systems. Despite their importance, it has been difficult to capture and characterize them in the same scaffold of either native enzymes or their synthetic analogs due to the distinct structural requirements of the three species, using redox reagents compatible with biomolecules under physiological conditions. Here, we report the realization of stepwise nitrosylation of a mononuclear nonheme iron site in an engineered azurin under such conditions. Through tuning the number of nitric oxide equivalents and reaction time, controlled formation of {FeNO}7 and {Fe(NO)2}9 species was achieved, and the elusive {FeNO}8 species was inferred by EPR spectroscopy and observed by Mössbauer spectroscopy, with complemental evidence for the conversion of {FeNO}7 to {Fe(NO)2}9 species by UV-Vis, resonance Raman and FT-IR spectroscopies. The entire pathway of the nitrosylation process, Fe(ii) → {FeNO}7 → {FeNO}8 → {Fe(NO)2}9, has been elucidated within the same protein scaffold based on spectroscopic characterization and DFT calculations. These results not only enhance the understanding of the dinitrosyl iron complex formation process, but also shed light on the physiological roles of nitric oxide signaling mediated by nonheme iron proteins., Stepwise nitrosylation from Fe(ii) to {FeNO}7, {FeNO}8 and then to {Fe(NO)2}9 is reported for the first time in the same protein scaffold, providing deeper understanding of the detailed mechanism of dinitrosyl iron complex formation.

Metal complexes of 1,2-diamidobenzenes have been long studied because of their intriguing redox properties and electronic structures. We present here a series of such complexes with 1,2-bis(sulfonamido)benzene ligands to probe the utility of these ligands for generating a large zero-field splitting (ZFS, D) in metal complexes that possibly act as single-ion magnets. To this end, we have synthesized a series of homoleptic ate complexes of the form (X)n[M{bis(sulfonamido)benzene}2] (n equals 4 minus the oxidation state of the metal), where M (Fe/Co/Ni), X [K+/(K-18-c-6)+/(HNEt3)+, with 18-c-6 = 18-crown ether 6], and the substituents (methyl and tolyl) on the ligand [bmsab = 1,2-bis(methanesulfonamido)benzene; btsab = 1,2-bis(toluenesulfonamido)benzene] were varied to analyze their effect on the ZFS, possible single-ion-magnet properties, and redox behavior of these metal complexes. A combination of X-ray crystallography, (spectro)electrochemistry, superconducting quantum interference device magnetometry, high-frequency electron paramagnetic resonance spectroscopy, and Mossbauer spectroscopy was used to investigate the electronic/geometric structures of these complexes and the aforementioned properties. These investigations show that the cobalt(II) complexes display very high negative D values in the range of -100 to -130 cm-1, and the nickel(II) complexes display very high positive D values of 76 and 58 cm-1. In addition, the cobalt(II) complexes shows barriers of 200-260 cm-1 and slow relaxation of the magnetization in the absence of an external magnetic field, underscoring the robustness of this class of complexes. The iron(II) complex exhibits a D value of -3.29 cm-1 and can be chemically oxidized to an iron(III) complex that has D = -1.96 cm-1. These findings clearly show that bis(sulfonamido)benzenes are ideally suited to stabilize ate complexes, to generate very high ZFSs at the metal centers with single-ion-magnet properties, and to induce exclusive oxidation at the metal center (for iron) despite the presence of ligands that are potentially noninnocent. Our results therefore substantially enhance the scope for this class of redox-active ligands.

Here we explore the electronic structure of the diiron complex [(dppf)Fe(CO)3]0/+ [10/+; dppf = 1,1'-bis(diphenylphosphino)ferrocene] in two oxidation states by an advanced multitechnique experimental approach. A combination of magnetic circular dichroism, X-ray absorption and emission, high-frequency electron paramagnetic resonance (EPR), and Mossbauer spectroscopies is used to establish that oxidation of 10 occurs on the carbonyl iron ion, resulting in a low-spin iron(I) ion. It is shown that an unequivocal result is obtained by combining several methods. Compound 1+ displays slow spin dynamics, which is used here to study its geometric structure by means of pulsed EPR methods. Surprisingly, these data show an association of the tetrakis[3,5-bis(trifluoromethylphenyl)]borate counterion with 1+.

The influence of different inorganic additives including KCl, HAuCl4·3H2O, Dy(NO3)3·xH2O, and La(NO3)3·6H2O on structure and magnetization of magnetite nanoparticles was studied. The nanoparticles were synthesized by electrocrystallization of iron plate using a chronoamperometric technique in an aqueous medium. X-ray diffraction patterns confirmed the formation of inverse cubic spinel structure of magnetite. Based on XRD results the variations of additive concentrations can improve or strongly change the structure of the samples. Electron microscopy images showed the mean particle size varies from 14 to 70 nm depending on the additive concentration. Room-temperature magnetization ranges from 45 to 84 Am2 kg−1, related to the particle size and additive concentration. It is possible to improve the structure and magnetization of particles by adding potassium chloride in the electrochemical cell. Mossbauer data show that the samples are slightly nonstoichiometric Fe3-δO4, with 0.01 ≤ δ ≤ 0.13. The paramagnetic doublet contribution highly changes in intensity with variation of additive and its concentration.

Single-crystal XRD structure of binuclear tetranitrosyliron complex [Fe2(SR)2(NO)4] (1), R = 4-aminothiophenyl, has been described. The properties of 1 were studied by IR, Mössbauer, mass spectroscopy, and amperometry. Complex 1 was shown to form long-living nitrosyl intermediates in solution, which underlies its prolonged NO donor activity. In HeLa cells, 1 caused accumulation of NF-κB p50 but decreased the levels of NF-κB p65 in the nucleus, which led to inhibition of NF-κB dependent genes. The complex also induced increase of p53 protein levels and p21 gene activity, which led to the apoptotic cell death after G2/M cell cycle phase.

Developing efficient catalytic materials and unveiling the active species are significant for selective hydrogenation of CO2 to C2+ hydrocarbons. Fe2 N@C nanoparticles were reported to exhibit outstanding performance toward selective CO2 hydrogenation to C2+ hydrocarbons (C2+ selectivity: 53.96 %; C2 -C4 = selectivity, 31.03 %), outperforming corresponding Fe@C. In situ X-ray diffraction, ex situ Mossbauer and X-ray photoelectron spectra revealed that iron nitrides were in situ converted to highly active iron carbides, which acted as the real active species. Moreover, the combined results of in situ diffuse reflectance infrared Fourier transform spectroscopy and control experiments suggested an in situ formed carbonyl iron-mediated conversion mechanism from iron nitrides to iron carbides.

Mossbauer spectroscopy, nuclear forward scattering, and Raman spectroscopy were applied to study redox transformations of the synthesized mixed-valence (III/V) antimony oxide. The transformations were induced by a culture of a hyperthermophilic archaeon of the genus Pyrobaculum. The applied methods allowed us to reveal the minor decrease of ca. 11.0 ± 1.2% of the antimony(V) content of the mixed-valence oxide with the concomitant increase of antimony(III). The method sensitivities for the quantitative assessment of the Sb(III/V) ratio have been considered.

Reduction of high spin paramagnetic complex [(κ2-P, P′-PCH2PCy)FeCl2] 2 by two electrons under N2 resulted in the formation of two isomeric low spin diamagnetic complexes 3trans and 3cis [Fe(κ3-P,C,P′-PCPCy)(H)2(N2)]. Cristallization allowed isolation of complex 3d [Fe(κ3-P,C,P′-PCPCy)(H)2]2(μ-N2), characterized by X-ray diffraction, Mossbauer and Raman spectroscopies. DFT calculations rationalized the facile double α,α CH bond insertion into a single sp3 CH2 moiety, as well as the fast exchange positions of the hydrides in the cis dihydride complex observed by NMR spectrocscopy.

A highly efficient photo-Fenton catalyst iron silicate glass was successfully prepared by a simple sol–gel method. The characterization results (XRD, Mössbauer spectroscopy, TEM, and FT- IR) showed that fayalite, clinoferrosilite and hematite nanoparticles were precipitated in the glass system. The catalytic activity of the glass samples was evaluated by measuring the degradation efficiency for organic dyes as well as for a typical persistent organic pollutant phenol, under visible light irradiation, in the presence of hydrogen peroxide (H2O2). The chemical oxygen demand (COD) and total organic carbon (TOC) were measured to see the progress in degradation of phenol. The results showed that the catalyst containing 20% iron had good catalytic properties for the degradation of both types of organic contaminants with superior stability for the degradation of methylene blue dye even after six cycles. Finally, a possible photocatalytic mechanism was proposed.

Single crystal X-ray diffraction, magnetic and 57Fe Mossbauer spectroscopic studies of a new iron(II)-based spin transition complex – [Fe(3-bpp)2](CF3COO)2 (bpp = 2,6-bis(pyrazol-3-yl)pyridine) are reported. The complex exhibits an incomplete thermal high spin (HS) low spin (LS) transition at ∼226 K which is not associated with any crystallographic transition. Only one of the two crystallographic iron(II) sites undergoes the spin transition, while the other HS site remains invariant of temperature down to 10 K. The origin of the incomplete spin transition is understood by analysing the nature of crystal packing below and above the transition temperature with special attention to the degree of distortion. The present study shows the role of the degree of distortion associated with the cations in the [Fe(3-bpp)2]2+ spin transition complexes.

Five-coordinate iron(III) complexes, (ImPh)2FeX (X = Cl (I), Br (II), I (III), N3 (IV)) containing two bidentate Schiff bases (N-benzylidene-2-hydroxy-3,5-di-tert-butylaniline (ImPh)H) and a halogen atom/azide group in the coordination sphere were synthesized and characterized in detail. According to the magnetic susceptibility measurements for polycrystalline samples of I–IV and Mossbauer spectroscopy data in the 2–300 K range, the complexes contain a high-spin metal ion (HS Fe3+, d5, SFe = 5/2). Compounds I–IV are stable in the crystalline state in the absence of oxygen or air moisture; however, in solution, they undergo symmetrization, resulting in the formation of the tris-ligand complex (ImPh)3Fe (V), which was also synthesized by the reaction (ImPh)H and FeCl3 (3 : 1). Unlike five-coordinate complexes I–IV, six-coordinate complex V contains low-spin iron(III) ion (LS Fe3+, d5, SFe = 1/2). The molecular structure of I was determined by X-ray diffraction (CIF file CCDC no. 1996527).

Mossbauer spectroscopy has been used to characterize oxygenated myoglobins (oxy Mbs) reconstituted with native and chemically modified 57Fe-enriched heme cofactors with different electron densities of the heme Fe atom (ρFe) and to elucidate the effect of a change in the ρFe on the nature of the bond between heme Fe and oxygen (O2), i.e., the Fe-O2 bond, in the protein. Quadrupole splitting (ΔEQ) was found to decrease with decreasing ρFe, and the observed ρFe-dependent ΔEQ confirmed an increase in the contribution of the ferric-superoxide (Fe3+-O2-) form to the resonance hybrid of the Fe-O2 fragment with decreasing ρFe. These observations explicitly accounted for the lowering of O2 affinity of the protein due to an increase in the O2 dissociation rate and a decrease in the autoxidation reaction rate of oxy Mb through decreasing H+ affinity of the bound ligand with decreasing ρFe. Therefore, the present study demonstrated the mechanism underlying the electronic control of O2 affinity and the autoxidation of the protein through the heme electronic structure. Carbon monoxide (CO) adducts of reconstituted Mbs (CO-Mbs) were similarly characterized, and we found that the resonance between the two canonical forms of the Fe-CO fragment was also affected by a change in ρFe. Thus, the nature of the Fe-ligand bond in the protein was found to be affected by the ρFe.

The protonation state of the iron(IV) oxo (or ferryl) form of ascorbate peroxidase compound II (APX-II) is a subject of debate. It has been reported that this intermediate is best described as an iron(IV) hydroxide species. Neutron diffraction data obtained from putative APX-II crystals indicate a protonated oxygenic ligand at 1.88 Å from the heme iron. This finding, if correct, would be unprecedented. A basic iron(IV) oxo species has yet to be spectroscopically observed in a histidine-ligated heme enzyme. The importance of ferryl basicity lies in its connection to our fundamental understanding of C─H bond activation. Basic ferryl species have been proposed to facilitate the oxidation of inert C─H bonds, reactions that are unknown for histidine-ligated hemes enzymes. To provide further insight into the protonation status of APX-II, we examined the intermediate using a combination of Mössbauer and X-ray absorption spectroscopies. Our data indicate that APX-II is an iron(IV) oxo species with an Fe─O bond distance of 1.68 Å, a K-edge pre-edge absorption of 18 units, and Mössbauer parameters of ΔE(q) = 1.65 mm/s and δ = 0.03 mm/s.

MgCexFe2-xO4 (0 ≤ x ≤ 0.2) nanoparticles have been produced by the glyco-thermal technique and characterized by X-ray diffraction, electron microscopy, X-ray photoelectron spectroscopy, Mossbauer spectroscopy and gas sensing analyses. The X-ray diffraction results indicated that a pure cubic spinel phase was formed for samples having a low concentration of Ce, but the high Ce doping (x = 0.2) of magnesium ferrite resulted in the formation of secondary phases. The crystallite size of the compounds ranged from 2.2 nm to 15.3 nm. The 57Fe Mossbauer spectra showed transformation from an ordered to a paramagnetic spin state with an increase in Ce concentration. Gas sensors fabricated from the spinel ferrites were tested towards various organic compound vapours (acetone, methanol, p-xylene, ethylbenzene, toluene, and benzene) at an operating temperature of 225 °C. The MgCe0.2Fe1.8O4 nanoferrite proved to possess quality sensor characteristics of high sensitivity and selectivity to acetone vapour, with a response of over 500@100 ppm concentration as well as reproducibility, reversibility, and stability of over 120 days. This sensor not only displayed high responses, but could also maintain them over 1, 3, 5, 10, 20, and 30 min of acetone exposure time. The sensor was resilient and sensitive to an oxygen reduced, inert ambient environment. Under relative humidity, the response was reduced, but stable, due to physisorbed water molecules.

The adsorption of the water-soluble tetra(p-sulphophenyl)porphyrin (TPPS) compound on Fe(II), Fe(III), Cu(II), Co(II), Ni(II), Zn(II), Cd(II), Sn(IV) and UO22+ metal ion-exchanged montmorillonite (MMT) facilitated the formation of the SAT metal-TPPS MMT complexes of these cations (where SAT indicates sitting atop, ie the metal is above the porphyrin plane and is bound to external ligands in this case the MMT surface). All the resulting powder samples have a brown-orange colour due to the presence of the metal-TPPS-MMT complexes of these cations. Heating the solid powder samples caused demetallation and changed the colour of the powder from brown-orange colour of the metal-TPPS-MMT complex to the green colour of the diacid porphyrin on the clay. When such samples were exposed to the open atmosphere where they could absorb water vapour, the brown-orange colour appeared again due to the remetallation. The cation remained in the vicinity of the TPPS molecule upon demetallation, which makes the metallation-demetallation process reversible. The TPPS has been found to be adsorbed only on the external surface, and can be intercalated using sodium ions in solution with the compound to open the clay lattice. The reactions were monitored using visible absorption spectra, diffuse reflectance spectra, Mössbauer spectroscopy and X-ray diffraction.

The high-spin (S = 5/ 2) meridional diastereoisomer of [Fe III(tpena)] 2+(tpena = N,N,N′-tris(2-pyridylmethyl)ethylendiamine-N′-acetate), mer-[Fe(tpena)] 2+, undergoes photolytic CO 2release to produce an iron(II) intermediate of a radical dihydroimidazopyridine ligand (L â). The structure of this unprecedented transient iron(II)(L â) complex is supported by UV-vis and Mössbauer spectroscopies, DFT calculations, as well as the X-ray structural characterization of an μ-oxo iron(III) complex of the oxidized derivative of L â, namely, [Fe III 2O(Cl) 2(L +) 2](ClO 4) 4(MeCN) 2(L += 2-(2-(bis(pyridin-2-ylmethyl)amino)ethyl)-2,3-dihydro-1H-imidazo[1,5-a]pyridin-4-ium). [Fe III 2O(Cl) 2(L +) 2] 4+is obtained only in the absence of O 2. Under aerobic conditions, O 2will intercept the iron(II)(L â) complex to form a putative Fe(III)-alkylperoxide complex which cascades to an iron(II) complex of SBPy3 (SBPy3 = N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-aldimine). Thus, through different oxidative pathways, the unknown ligand L +or SBPy3 forms by loss of a one-carbon-atom or a two-carbon-atom unit, respectively, from the glycyl arm of tpena. Acceleration of the photodecarboxylation step is achieved by addition of thiocyanate because of transient formation of a more photoreactive NCS -adduct of [Fe(tpena)] 2+. This has allowed for kinetic observation of the reaction of [Fe II(L â)] 2+with O 2which is, unexpectedly, promoted also by light. We propose that this corresponds to the energy needed for the conversion of the ring-closed radical ligand L âto a ring-opened tautomer to allow for O 2insertion between the C and Fe atoms of the iron(II) complex.

The magnetic structure and the composition of Fe3O4/γ-Fe2O3 nanoparticles are studied at 300 and 80 K with Mossbauer spectroscopy. We found that the Fe3O4/γ-Fe2O3 particles are a core–shell nanocomposite (NC), in which magnetite Fe3O4 is covered with a maghemite shell (γ-Fe2O3). We showed that the thickness of the maghemite shell (γ-Fe2O3) depends on synthesis technology. We found that a layer, whose magnetic structure differs from that of the inner part of the shell (γ-Fe2O3), is formed on the surface of the maghemite shell (γ-Fe2O3) in the Fe3O4/γ-Fe2O3 NC. An intermediate layer is formed in the spin-glass state between the core and the shell. The data on structure of core–shell nanocomposites open up prospects to explain the properties of such particles, which are of great interest to use in various fields, including biomedicine.

Nuclear gamma resonance (NGR) is used to study powders of externally homogeneous magnetite-like substances that form in the reaction between 1,1'-diacetylferrocene and e-caprolactam or 2-aminoethanesulfonic acid in a relatively low range of temperatures (100–180°C). The powders are shown to consist of magnetite and a ferrocene-containing matrix that contains 1,1'-diacetyleferrocene and an organic nitrogen-containing component. In studying the temperature dependence of the NGR spectra in the range of 295–80 K, it is established that a fast effective exchange of electrons occurs in the samples both internally and between two Fe2+/Fe3+ subsystems, ferrocene/ferricenium and sublattice B of magnetite. As a result, classical mechanisms of electron exchange retardation and the phase ordering of the magnetite structure do not work, and no Verwey transition is observed in the samples.

Fe@SiO2 core–shell model catalysts were investigated for the conversion of CO2 and H2 into CH4, CO and H2O. For evaluation of the effect of core size on the catalytic activity, samples with Fe particle sizes of 4, 6 and 8 nm were prepared. Fresh and spent catalysts were thoroughly characterized by X-ray diffraction, 57Fe Mössbauer spectroscopy, transmission electron microscopy, temperature programmed hydrogenation and X-ray photoelectron spectroscopy. As a result, the yield of the major product CO as well as CH4 was increased with Fe core size. Additionally, growing Fe cores led to stronger carburization and higher amount of reactive carbide entities, which drive the CH4 formation. Finally, formation of inactive bulk carbon deposition is strongly suppressed for the core–shell catalysts in comparison to bulk iron oxide catalysts used for CO2 hydrogenation.