Search

Nitrides represent a promising class of materials for a variety of applications. However, bulk synthesis remains a challenging task due to the stability of the N2 molecule. In this study, we introduce a simple and scalable approach for synthesizing nitride bulk materials. Moderate reaction temperatures are achieved by using reactive starting materials, slow and continuous mixing of the starting materials, and by dissipating heat generated during the reaction. The impact on the synthesis of using different starting materials as nitrogen source and the influence of a flux were examined. γ‐Sn3N4 was selected as the model compound. The synthesis of pure γ‐Sn3N4 bulk material on a large scale has still been a challenge, although a few synthesis methods were already described in the literature. Here we synthesized γ‐Sn3N4 by metathesis reaction of argon‐diluted SnCl4 with Li3N, Mg3N2 or Ca3N2 as nitrogen sources. Products were characterized by powder X‐ray diffraction, scanning and transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, dynamic flash combustion analysis, hot gas extraction analysis, X‐ray photoelectron spectroscopy, Mössbauer spectroscopy and X‐ray absorption and emission spectroscopy. Additionally, single‐crystal diffraction data of γ‐Sn₃N₄, previously unavailable, were successfully collected. [ABSTRACT FROM AUTHOR]

The ligand susan6−Me (susan6−Me=4,7‐dimethyl‐1,1,10,10‐tetra(6‐methyl‐2‐pyridylmethyl)‐1,4,7,10‐tetraazadecane) allows the synthesis of a peroxo complex that is only a transient species under catalytic conditions with the closely related ligand susan (susan=4,7‐dimethyl‐1,1,10,10‐tetra(2‐pyridylmethyl)‐1,4,7,10‐tetraazadecane). For the synthesis of a peroxo complex analogous to that of susan6−Me we present here the three air‐sensitive complexes [(susan){FeIICl2}2], [(susan){FeII(OTf)2}2], and [(susan){FeII(μ‐OH)2FeII}](ClO4)2 as potential precursors. [(susan){FeII(μ‐OH)2FeII}](ClO4)2 shows weak antiferromagnetic coupling and a g=16 EPR signal. Dissolving [(susan){FeII(OTf)2}2] in CH3CN forms [(susan){FeII(CH3CN)2}2]4+ that shows a spin transition upon cooling as evidenced by UV‐Vis, 1H NMR, and Mössbauer spectroscopies. In the UV‐Vis‐NIR spectra the combination of (i) the energy of the MLCT, (ii) the energy, and (iii) the splitting of the d–d transitions provide insight into the overall electron donation and into the different σ‐donor/π‐donor/π‐acceptor capabilities of the exogenous ligands. These experimental signatures provide insight into the molecular structures in solution e. g. during reactions with O2. [ABSTRACT FROM AUTHOR]

Herein, NaxFe1–yMnyO2 (y = 0.4, 0.5, 0.6, 0.7, and 0.8) oxides, which are a potential cathode materials group for Na‐ion batteries, are presented. Samples are prepared by solid‐state synthesis and crystallized in P2‐type structure (P63/mmc). Mössbauer spectroscopy studies revealed that in pristine and deintercalated samples the whole iron occurs at a high‐spin Fe3+ state. Electrochemical impedance spectroscopy measurements exhibited the thermally activated electrical conductivity of Na0.67Fe1–yMnyO2 with relatively high activation energies (≈0.4 eV). Obtained results are supported by the electronic structure calculations (KKR‐CPA method), which indicates that total density of states at the Fermi level increases with manganese content in the sample. Electrochemical properties of Na|Na+|NaxFe1–yMnyO2 test cells and the specific charge/discharge capacities analysis confirmed that only the manganese ions in NaxFe1–yMnyO2 are active in electrochemical processes and higher content of manganese results in obtaining higher specific capacities (≈150 mAh g−1 for y = 0.8 under C/10 current load). [ABSTRACT FROM AUTHOR]

The core@shell nanostructures were obtained in the process of transformation of ferrocene Fe(C 5 H 5) 2 at high pressure (HP) of 8 GPa and high temperature (HT) of 900 °C with an isothermal exposure time t varying from 10 to 10000 s. At t > 300 s, the iron carbide o-Fe 7 C 3 nanoparticles with an orthorhombic crystal structure (sp.gr. Pnma) can be created, which are dispersed in highly defective carbon matrix. After opening the high-pressure cell, a series of redox reactions occurs, leading to a formation of iron oxides on the surface of the iron carbide core. When the size of Fe 7 C 3 nanoparticle is less than critical one the nanoparticle is fully oxidized, while in the larger particle an amorphous iron oxide shell is formed. A sequential increase in t initiates crystallization processes both in the iron carbide subsystem and in the carbon subsystem, resulting in the formation of core@shell Fe 7 C 3 /Fe x O y /C structures. Iron oxides with a cubic spinel-type structure (Fe 3 O 4 /γ-Fe 2 O 3) appear in the shell. However, under oxygen reduction, part of magnetite can be transformed into wüstite FeO. The magnetic properties of magnetite and wüstite are radically different, and by varying the thickness of these layers, structures with the desired functional properties can be obtained. [Display omitted] [ABSTRACT FROM AUTHOR]

The commercial success of the electrochemical energy conversion technologies required for the decarbonization of the energy sector requires the replacement of the noble metal‐based electrocatalysts currently used in (co‐)electrolyzers and fuel cells with inexpensive, platinum‐group metal‐free analogs. Among these, Fe/N/C‐type catalysts display promising performances for the reduction of O2 or CO2, but their insufficient activity and stability jeopardize their implementation in such devices. To circumvent these issues, a better understanding of the local geometric and electronic structure of their catalytic active sites under reaction conditions is needed. Herein we shed light on the electronic structure of the molecular sites in two Fe/N/C catalysts by probing their average spin state with X‐ray emission spectroscopy (XES). Chiefly, our in situ XES measurements reveal for the first time the existence of reversible, potential‐induced spin state changes in these materials. [ABSTRACT FROM AUTHOR]

A novel approach for the synthesis of Fe(0) nanoparticles (NPs) with tunable sizes and shapes is reported. Ultrasmall Fe(0) NPs were reacted under mild conditions in the presence of a mixture of palmitic acid and amine ligands. These NPs acted not only as preformed seeds but also as an internal iron(II) source that was produced by the partial dissolution of the NPs by the acid. This fairly simple approach allows the strict separation of the nucleation and the growth steps. By changing the acid concentration, a fine tuning of the relative ratio between the remaining Fe(0) seeds and the iron(II) reservoir was achieved, giving access to both size (from 7 to 20 nm) and shape (spheres, cubes or stars) control. The partial dissolution of the ultrasmall Fe(0) NPs into iron(II) source and the successive growth was further studied by using combined TEM and Mössbauer spectroscopy. The successive corrosion, coalescence, and ripening observed could be understood in the framework of an environment‐dependent growth model. Ripe fruits: Ultrathin Fe(0) nanoparticles can be used as an iron source for the size and shape control of metallic NPs in a nanoparticle ripening process. By adjusting the atmosphere, isotropic growth or oriented attachment can be selectively favored. The key role played by hydrogen gas in the final faceting was demonstrated, and leads to highly crystalline Fe nanostars or nanocubes. [ABSTRACT FROM AUTHOR]

Two series of magnetic nanopowders were synthesized at room temperature starting from a mixture of iron II and III precursors, FeSO4 and FeCl3, respectively. Precipitation agents, as KOH and NaOH were used. While the concentration of the added ferrous and ferric solutions ranged between 0.1 M and 0.0125 M, the hydroxide solution concentration was maintained constant (1 M). TEM images of the samples showed that the particles shape changes from quasi spherical to spherical. For both series the crystallite size decreases with iron concentration, from 9 to 2 nm for KOH series and from 10 to 3 nm for NaOH series. Moessbauer Spectroscopy was signaling only Fe3+ in the final spinel product. BET measurements revealed the material mesoporosity and fractal structure of maghemite nanoparticles that explain the unusual high surface area, ~240 m2/g. All the samples actually exhibit superparamagnetic behavior at room temperature with saturation magnetization up to 73 emu/g value closed to those of bulk maghemite. [ABSTRACT FROM AUTHOR]

Abstract: Reaction of the unsymmetrically armed pincer PNNH (phosphine‐pyridyl‐pyrazole) ligand with FeCl2 yielded the five‐coordinate monomer [(PNNH)FeCl2], the NH proton of which captures THF through the formation of a hydrogen bond. Deprotonation of this NH functionality with Li[N(SiMe3)2] did not give the four‐coordinate [(PNN)FeCl], but instead retained LiCl to yield [(PNNLi)FeCl2], in which the lithium bridges between the pyrazolate β‐nitrogen and one of the chlorides on iron. One‐electron reduction of this compound under CO occurred with the loss of LiCl to form the square‐pyramidal monovalent iron in [(PNN)Fe(CO)2], which was characterized by IR, Mössbauer, and EPR spectroscopy, X‐ray diffraction, and DFT calculations. Cyclic voltammetry studies of [(PNN)Fe(CO)2] showed a reversible reduction wave and the reduction product was synthesized by using KC8. The product K[(PNN)Fe(CO)2] contains saturated, five‐coordinate Fe0; the (PNN)Fe subunit is anionic and the K+ cations cluster close to the pyrazolate side of the two CO ligands. Potassium electrophile complete its coordination sphere through interactions with the oxygen atom of a CO of a neighboring unit, thereby creating a polymeric chain. The reaction of [(PNN)Fe(CO)2] with HBpin (4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolane) resulted in the reduction of the metal center (by release of H2) and borylation of the pyrazole β‐nitrogen atom. This redox‐active addition of the H−B bond across the metal–ligand assembly is an unusual example of metal–ligand cooperativity and establishes a ligand that supports iron in three different oxidation states. [ABSTRACT FROM AUTHOR]

The spin state of catalytically active 3d metal centers plays a significant role in their activity in enzymatic processes and organometallic catalysis. Here the catalytic activity of an FeII coordination compound that can undergo a cooperative switch between low-spin (LS) and high-spin (HS) states is reported. Catalytic measurements in the temperature range 291-318 K revealed a drastic drop of the catalytic activity on conversion of the metal centers from the LS to the HS form. For thermoswitchable complex [Fe(NH2trz)3]Br2 (NH2trz = 4-amino-1,2,4-tiazole; Tup = 305 K), the activation energy is found to be considerably lower for the LS state (158 kJ mol-1) compared to the HS state (305 kJ mol-1). Mössbauer analysis revealed that this is related to higher conversion of the LS complex on oxidation. Comparisons with another polymorph of [Fe(NH2trz)3]Br2 (Tup = 301 K) and [Fe(NH2trz)3](ClO4)2 (Tup = 240 K) are made. These results show the potential of spin-crossover compounds to compare the catalytic activity of different spin states of the same material when other means of differentiation are limited. [ABSTRACT FROM AUTHOR]

Samples of sphero-conical vessels found in mass quantities in the ancient settlement Bolgar were analyzed by Moessbauer spectroscopy. Wares with relatively low annealing temperatures <500°C and having a ratio Fe/Fe ≤ 1.11 in transmission spectra were differentiated from those with high ones. The detected value of $$ {\mathrm{Fe}}_{\mathrm{par}}^{3+} $$ /Fe was considerably less than the value of 2.69 that was characteristic of raw materials for pottery production in the vicinity of the selected settlement. This indicated that other non-local sources of raw materials existed in the medieval handicraft center. [ABSTRACT FROM AUTHOR]

The initial stage of transformation of pyrite to Fe(II)-sulfate as a result of mechanical milling is studied by X-ray powder diffraction (XRD), Moessbauer spectroscopy (MS), Infrared (IR) and X-ray photoelectron spectroscopy (XPS) techniques. A degree of conversion of 0.071 is achieved in the time interval of 0 36 min. The kinetic data satisfy the equation of a shrinking core reaction 1-(1-α)1/3=kt. The reaction is of the first order. The calculated rate constant is k=6.434.10-4 min-1. .

The reaction of the ferrocene-bridged bis(imidazolin-2-imine) ligand N, N′-bis(1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene)-1,1′-ferrocenediamine [fc(NIm)2] with MCl2 salts furnished the complexes [{fc(NIm)2}MCl2] (M = Mn, Fe, Co, Ni, Cu, Zn), which were structurally and spectroscopically characterized. The iron complex was oxidized by reaction with ferrocenium hexafluoroantimonate, and both compounds, [{fc(NIm)2}FeCl2] and [{fc(NIm)2}FeCl2]SbF6, were further studied by means of Mössbauer spectroscopy, SQUID magnetometry, and single-crystal X-ray diffraction, revealing that oxidation occurred at the tetrahedral FeN2Cl2 moiety. The CuX (X = Cl, Br, I) complexes of fc(NIm)2 were synthesized, affording dimeric (X = Cl, Br) or polymeric (X = I) structures. In addition, the ligand bis( N, N, N′, N′-tetraisopropyl-2,3-diaminocyclopropen-1-ylidene)-1,1′-ferrocenediamine [fc(NCyp)2], was prepared and the trimetallic complex [{fc(NCyp)2}Pd2Cl4] was synthesized and structurally characterized. The attempted synthesis of the corresponding nickel complex furnished single crystals of the composition [{fc(NHCyp)2}Cl(NiCl3)]; X-ray diffraction analysis afforded the first crystal structure of the [Ni2Cl6]2- anion. [ABSTRACT FROM AUTHOR]

We present a new microscopic approach for the description of the effects of an external direct current (dc) electric field on the magnetic, polarizability, and spectroscopic characteristics of molecular crystals containing cyanide-bridged Fe-Co clusters as structural units. In addition to the interaction with the electric field, the model allows for metal-metal electron transfer, intracluster magnetic exchange, and long-range electron-deformational interactions, which are taken into account within the mean-field approach. The external electric field gives a unique possibility to manipulate the polarizability, magnetic, and spectroscopic characteristics of cyanide-bridged Fe-Co clusters. [ABSTRACT FROM AUTHOR]

The anionic L = [(EP iPr2)2N]- (E = S, Se) form of the dichalcogenidoimidodiphosphinato-type ligands containing iPr peripheral groups has been shown previously to afford tetrahedral [MIIL2] complexes (E = S, M = Mn, Co, Ni, Zn; E = Se, M = Co, Ni, Zn). The syntheses of the analogous [FeL2] complexes [E = S ( 1), Se ( 2)] were performed in this work through metathesis reactions between FeCl2 and the corresponding KL salts. For both 1 and 2, X-ray crystallography revealed two distinct molecules in the asymmetric unit. Complexes 1 and 2 are isostructural and exhibit P-E and P-N bond-length differences compared with those of the free ligands, and these differences are translated into shifts of the corresponding IR bands. Cyclic voltammetry studies showed that the FeII → FeIII oxidation in 2 occurs at a lower potential than that of 1. The zero-field Mössbauer spectra of the two complexes are quite similar and provide evidence of similar S = 2 electronic structures. The observation of crystallographically distinct FeIIE4 sites for both 1 and 2 is also revealed in the corresponding Mössbauer spectra. Complex 2 was employed as a single-source precursor in catalyst-aided chemical vapor deposition experiments, which afforded the iron selenides FeSe and Fe3Se4. [ABSTRACT FROM AUTHOR]

Five new spin crossover complexes with 4- and 5-(phenylazo)-2,2-bipyridine (4-/5-PAbipy) ligands were synthesized and investigated with respect to their spin crossover (SCO) behavior. The results are compared to the thermal and light-induced spin transition properties of the parent SCO complexes [Fe(bpz)2(bipy)] ( 1) and [Fe(bipy)2(NCS)2] ( 2). [Fe(bpz)2(4-PAbipy)] ( 1a) undergoes a stepwise spin transition whereas [Fe(bpz)2(5-PAbipy)] ( 1b) exhibits a one-step transition with a 6 K-wide hysteresis. For [Fe(bpz)2( tBu5-PAbipy)] ( 1c) the spin transition to the low-spin state is incomplete. Qualitatively similar changes of the SCO behavior are observed for the complexes [Fe(4-PAbipy)2(NCS)2] ( 2a) and [Fe(5-PAbipy)2(NCS)2] ( 2b). In comparison to the parent system 2, a strengthening of intermolecular interactions leads to a stabilization of the low-spin state. Evidence for the LIESST behavior could be obtained for all new compounds by means of magnetic susceptibility measurements as well as UV/Vis and resonance Raman spectroscopy. [ABSTRACT FROM AUTHOR]

A series of 57Fe-doped TiO2 and 57Fe/Sn-codoped TiO2 materials were prepared by a soft-chemical solution process with various 57Fe concentrations from 0.1 to 1.0 at.-% and a fixed Sn concentration of 2.0 at.-%. In this process, an aqueous H2O2 solution reacts with iron and titanium or iron, tin, and titanium precursor compounds to produce peroxopolymetallic acids. The structures and magnetic properties of the products were characterized by magnetic-moment measurements, X-ray diffraction, and Raman and Mössbauer spectroscopy. The results showed that all samples consisted of a rutile phase (and a trace amount of anatase in 57Fe-TiO2). All samples exhibited hysteresis loops in the M- H curves, which demonstrated the presence of room-temperature ferromagnetism. In addition, their magnetic properties decreased with increasing degree of 57Fe doping. Oxygen vacancies were considered to be responsible for the presence of ferromagnetism. [ABSTRACT FROM AUTHOR]

Pure powder and small single crystals of BaFe2S2O were obtained by solid-state reaction between BaO, Fe, and S in closed silica ampoules. The crystal structure contains a magnetic ladderlike sublattice of high-spin Fe2+ (d6) tetrahedrally coordinated by three S and one O atoms. Strong antiferromagnetic spin interactions are observed far above the Néel transition ( TN = 260 K). 57Fe Mössbauer spectra show typical features of Fe2+ as a doublet with large quadrupole splitting above TN and combined electric and magnetic hyperfine interaction in the magnetically ordered phase. A structural transition upon the magnetic order is discussed. [ABSTRACT FROM AUTHOR]

Reaction of 1,1′-ferrocenedicarbonyl chloride with 3-ethyl-2,4-dimethylpyrrole in DCM produced the half-way product, namely, the ferrocene bis(2-ketopyrrole) derivative 2 and not the expected bis(dipyrromethene) compound. The 2-ketopyrrole compound readily reacted with BF3 ·Et2O to produce the bis(difluoropyrrolo)-oxaborole compound, FBF, as a red/brown solid which was characterised by X-ray crystallography. 57Fe Mössbauer spectra for 2 and FBF were consistent with low-spin iron(II) (d6) ferrocene derivatives. A cyclic voltammogram for 2 in acetonitrile revealed a reversible wave at +0.31 V vs. Fc+/Fc (ferrocene-based) and an irreversible wave at -2.38 V vs. Fc+/Fc (ketopyrrole-based). The electrochemical behaviour is severely perturbed by the chelation of the BF2 groups. Alterations to the electronic properties of 2 by formation of FBF are also evident in the absorption profiles. DFT calculations [B3PW91, 6-31G(3df)] support the observed changes in the electrochemistry findings and the Mössbauer spectroscopic data. [ABSTRACT FROM AUTHOR]

Two [FeLn2Fe(μ3-OH)2(teg)2(N3)2(C6H5COO)4] compounds (where Ln=YIII and DyIII; teg=triethylene glycol anion) have been synthesized and studied using SQUID and Mössbauer spectroscopy. The magnetic measurements on both compounds indicate dominant antiferromagnetic interactions between the metal centers. Analysis of the 57Fe Mössbauer spectra complement the ac magnetic susceptibility measurements, which show how a static magnetic field can quench the slow relaxation of magnetization generated by the anisotropic DyIII ions. [ABSTRACT FROM AUTHOR]

The synthesis, structure, and magnetism of a nonanuclear iron(III) phosphonate, [Fe9III(μ3-O)4(O3PC5H9)3(O2CCMe3)13] ·(EtOH)0.5 ·(Et2O)0.5 ( 1), is described. Compound 1 was obtained in the direct reaction of anhydrous ferric chloride, cyclopentylphosphonic acid, and pivalic acid in the presence of triethylamine. Compound 1 possesses a distorted icosahedral structure; nine of the vertices are occupied by FeIII, whereas three others are occupied by the phosphorus atoms of the cyclopentylphosphonate ligand. Mössbauer spectroscopy of 1 confirms the presence of high-spin FeIII. Low-temperature magnetic studies reveal the presence of strong antiferromagnetic coupling between the Fe3+ ions. [ABSTRACT FROM AUTHOR]

The heterodinuclear mixed-valence complex [FeMn(ICIMP)(OAc)2Cl] ( 1) {H2ICIMP = 2-( N-carboxylmethyl)-[ N-( N-methylimidazolyl-2-methyl)aminomethyl]-[6-( N-isopropylmethyl)-[ N-( N-methylimidazolyl-2-methyl)]aminomethyl-4-methylphenol], an unsymmetrical N4O2 donor ligand} has been synthesized and fully characterized by several spectroscopic techniques as well as by X-ray crystallography. The crystal structure of the complex reveals that both metal centers in 1 are six-coordinate with the chloride ion occupying the sixth coordination site of the MnII ion. The phenoxide moiety of the ICIMP ligand and both acetate ligands bridge the two metal ions of the complex. Mössbauer spectroscopy shows that the iron ion in 1 is high-spin FeIII. Two quasi-reversible redox reactions for the complex, attributed to the FeIIIMnII/FeIIMnII (at -0.67 V versus Fc/Fc+) and FeIIIMnII/FeIIIMnIII (at 0.84 V), were observed by means of cyclic voltammetry. Complex 1, with an FeIII-MnII distance of 3.58 Å, may serve as a model for the mixed-valence oxidation state of purple acid phosphatase from sweet potato. The capability of the complex to effect organophosphate hydrolysis (phosphatase activity) has been investigated at different pH levels (5.5-11) by using bis(2,4-dinitrophenyl)phosphate (BDNPP) as the substrate. Density functional theory calculations indicate that the substrate coordinates to the MnII ion. In the transition state, a hydroxide ion that bridges the two metal ions becomes terminally coordinated to the FeIII ion and acts as a nucleophile, attacking the phosphorus center of BDNPP with the concomitant dissociation of the leaving group. [ABSTRACT FROM AUTHOR]

Anionic cobalt and iron metallalumatranes that bind dinitrogen in an end-on fashion were prepared and characterized by X-ray crystallography. Along with literature-known neutral cobalt and iron metallalumatranes, they form a quartet of low-valent coordination complexes for comparing dinitrogen activation and functionalization at cobalt versus iron centers. In the anionic metallalumatranes, the metal atoms are proposed to have subvalent oxidation states of -1. The electronic structure of the anionic iron alumatrane, which was probed by electron paramagnetic resonance spectroscopy, Mössbauer spectroscopy, and density functional theory, is most consistent with Fe(-1)→Al(+3). Functionalization of dinitrogen was achieved by reaction of the ferrate alumatrane with 1,2-bis(chlorodimethylsilyl)ethane and KC8 (1 equiv.) to generate an iron(II) disilylhydrazido complex. The transformation of dinitrogen to disilylhydrazido(2-) is an overall four-electron process. [ABSTRACT FROM AUTHOR]

A dinuclear Pd-Sn bonded complex is reported, in which the interaction of the formally tin(II)-based ligand, [2-MeBrSnC6F4AsPh2]-, with palladium appears to be best described as PdI-SnIII or Pd0-SnIV. [ABSTRACT FROM AUTHOR]

Abstract: Zero-valent iron nanoparticles (NZVI) which are frequently investigated for their application potential in pollutants removal can be prepared by several different ways. Here, we report NZVI formation by wet chemical synthesis in the presence of selected L-amino acids, thus low-molecular weight and biocompatible species. According to our results based mainly, but not only, on Mössbauer spectroscopy (an excellent iron sensitive method), there are distinct differences in zero-valent iron content when each of the amino acids under study mediated NZVI formation. The content of iron atoms in the oxidation state of zero is one of crucial parameters when considering the reductive mode of NZVI action against pollutants. For instance, while the presence of L-glutamic acid promoted NZVI generation, L- cysteine hindered it completely. The effect of L-arginine and L-glutamine presence during NZVI formation was also investigated and evaluated. Moreover, the influence of acidic and alkaline pH values on NZVI formation in the presence of all four selected L-amino acids was looked into. It turned out that acidic and alkaline pH values have negative effects on NZVI formation in the presence of L-glutamic acid and L-glutamine. On the contrary, almost no effect of pH was observed for L-cysteine and L-arginine. [Copyright &y& Elsevier]

A mononuclear iron(II) compound 1 of the general formula [Fe( L)2](ClO4)2 { L = 4-[2,6-bis(pyrazol-1-yl)pyridin-4-yl]benzaldehyde} was prepared and structurally characterised. Single-crystal X-ray structure analysis revealed the presence of a complex dication [Fe( L)2]2+ and two ClO4- counteranions within the unit cell. The bond lengths and angles within the coordination polyhedron FeN6 indicate the low-spin state of the central iron(II) metal ion at T = 180 K. Magnetic investigations elucidate spin crossover with T1/2 = 285 K. The experimental magnetic susceptibility data could be satisfactorily fitted with the Curie law in combination with the Ising-like model. The room-temperature character of the spin crossover was further studied by variable-temperature far-IR, Vis and Mössbauer spectroscopy. Laser irradiation of 1 carried out at 10 K gives rise to a complete low-spin to high-spin photoconversion. A subsequent temperature-dependent investigation revealed the existence of a photoexcited metastable HS state up to TLIESST = 70 K (LIESST = light-induced excited-spin-state trapping) as well as the presence of a light-induced thermal hysteresis loop with a width of 10 K. [ABSTRACT FROM AUTHOR]

The crystallographic and electronic structure of shandite-type InSnCo3S2 was reinvestigated. Single-crystal and powder X-ray diffraction, 119Sn Mößbauer spectroscopy, and DFT studies focused on the relation between the In-Sn ordering and a recently predicted semiconductor-to-metal transition. One aim of the combined experimental and theoretical approach was to show how the occupation of Sn and In sites causes structural distortions. The second aim was to point out effects on the electronic structure and the relative stability of structural variants with respect to In-Sn ordering. The interpretation of both X-ray diffraction and Mößbauer spectroscopy data by DFT calculations helped to understand the effects from a nonlocal and a local point of view. This is a starting point of materials design for various applications. [ABSTRACT FROM AUTHOR]

Abstract: The iron uptake and storage systems of terrestrial/higher plants are now reasonably well understood with two basic strategies being distinguished: strategy I involves the induction of a Fe(III)-chelate reductase (ferrireductase) along with Fe(II) or Fe(III) transporter proteins while strategy II plants have evolved sophisticated systems based on high-affinity, iron specific, binding compounds called phytosiderophores. In contrast, there is little knowledge about the corresponding systems in marine, plant-like lineages. Herein we report a study of the iron uptake and storage mechanisms in the green alga Tetraselmis suecica. Short term radio-iron uptake studies indicate that iron is taken up by Tetraselmis in a time and concentration dependent manner consistent with an active transport process. Based on inhibitor and other studies it appears that a reductive–oxidative pathway such as that found in yeast and the green alga Chlamydomonas reinhardtii is likely. Upon long term exposure to 57Fe we have been able, using a combination of Mössbauer and X-ray absorption spectroscopies, to identify three metabolites. The first exhibits Mössbauer parameters typical of a [Fe4S4]2+ cluster and which accounts for approximately 10% of the total intracellular iron pool. The second displays a spectrum typical of a [FeIIO6] system accounting for approximately 2% of the total pool. The largest component (ca. 85+%) consists of polymeric iron-oxo mineral species with parameters between that of the crystalline ferrihydrite core of animal ferritins and the amorphous hydrated ferric phosphate of bacterial and plant ferritins. [Copyright &y& Elsevier]

The five-membered electron-transfer series [M(bpy)3] n and [M(tpy)2] n (M = Fe, Ru; bpy = 2,2′-bipyridine, tpy = 2,2′:6′,2″-terpyridine) and [Fe(tbpy)3] n (tbpy = 4,4′-di- tert-butyl-2,2′-bipyridine; n = 3+, 2+, 1+, 0, 1-) have been investigated and the electronic structure of the so called 'low-valent' complexes ( n = 1+, 0, 1-) have been established by a combination of electro- and magnetochemistry, electron paramagnetic resonance (EPR) and Mössbauer spectroscopy, X-ray crystallography, and DFT calculations. These complexes are accessed by reduction of the d6 S = 0 dicationic starting materials [M(bpy)3]2+ and [M(tpy)2]2+ (M = Fe, Ru) and [Fe(tbpy)3]2+. The monocations [M(bpy ·)(bpy0)2]1+ ( S = 1/2) and [M(tpy ·)(tpy0)]1+ ( S = 1/2) (M = FeII, RuII) also contain a low-spin (t2g)6 divalent metal center, plus a single radical monoanion (bpy ·)1- or (tpy ·)1-, and two or one neutral (bpy0) or (tpy0) ligands, respectively. The unpaired electron resides in a ligand π* orbital. The neutral complexes [FeII(bpy ·)2(bpy0)]0 and [RuII(tpy ·)2]0 were found, by DFT calculations, to possess an S = 1 ground state that is attained by weak intramolecular ferromagnetic coupling between two ligand radical anions and a singlet excited state ( S = 0). In contrast, the neutral species [RuII(bpy ·)2(bpy0)]0 possesses an S = 0 ground state. The metal centers of these neutral complexes retain a low-spin (t2g)6 configuration. Remarkably, the corresponding neutral complex [FeII(tpy ·)2]0 contains high-spin FeII ( SFe = 2). Strong intramolecular antiferromagnetic metal-radical coupling yields an experimentally observed S = 1 ground state. The monoanions [MII(bpy ·)3]1- (M = Fe, Ru) are composed of a low-spin metal ion [Fe, Ru; (t2g)6; SM = 0] and three (bpy ·)1- radical anions. [ABSTRACT FROM AUTHOR]

The triangular complex [FeIII3(μ3-O)(μ-4-O2N-C3H2N2)6Br3]2- has been characterized and studied by magnetic susceptibility measurements, 57Fe Mössbauer and electron paramagnetic resonance (EPR) spectroscopic methods. A combination of experimental and computational results has allowed the differentiation between two sets of acceptable isotropic exchange constants. The magnetic exchange within this complex has been modelled by a spin Hamiltonian involving antiferromagnetic exchange constants of average value Jav = -81.4 cm-1 and an antisymmetric exchange | dz| = 1.40 cm-1. [ABSTRACT FROM AUTHOR]

We report a new chemical approach toward air-stable nanoscale zero-valent iron (nZVI). The uniformly sized (approx. 80 nm) particles, formed by the reduction of Fe(II) salt by borohydride in the presence of glutamic acid, are coated by a thin inner shell of amorphous ferric oxide/hydroxide and a secondary shell consisting of glutamic acid. The as-prepared nanoparticles stabilized by the inorganic-organic double shell create 2D chain morphologies. They are storable for several months under ambient atmosphere without the loss of Fe(0) relative content. They show one order of magnitude higher rate constant for trichlorethene decomposition compared with the pristine particles possessing only the inorganic shell as a protective layer. This is the first example of the inorganic-organic (consisting of low-molecular weight species) double-shell stabilized nanoscale zero-valent iron material being safely transportable in solid-state, storable on long-term basis under ambient conditions, environmentally acceptable for in situ applications, and extraordinarily reactive if contacted with reducible pollutants, all in one. [ABSTRACT FROM AUTHOR]

Series of Fe and Fe-Me (Me = Pt or Pd) catalyst supported on γ-AlO, TiO (anatase) or diatomite were prepared by the incipient wetness impregnation method. The metal loading was 8 wt.% Fe and 0.7 wt.% noble metal. The preparation and pretreatment conditions of all studied samples were kept to be the same. X-ray diffraction, Moessbauer spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed reduction are used for characterization of the supports and the samples at different steps during their treatment and catalytic tests. The catalytic activity of the samples was tested in the reaction of total benzene oxidation. The physicochemical and catalytic properties of the obtained materials are compared with respect of the different chemical composition, dispersion of used carriers and of the supported phases. Samples with the same composition prepared by mechanical mixing are studied as catalysts for comparison and for clearing up the presence of size-dependent effect, also. [ABSTRACT FROM AUTHOR]

Metal complexes were prepared on the basis of polymer ligands with carboxylic and nitrogen-containing functionalities by complexation with iron ions in aqueous solutions of FeCl3·6H2O and FeSO4·2H2O. The degree of introduction of iron ions into the polymer matrices depended on the relative content of the functional groups in the polymers studied such as polyacrylic acid, poly-4-vinylpyridine, and poly(2- N,N-dimethylaminoethyl) methacrylate. The metal content in the polymer complexes was found to vary between 9.0 and 30.0 (for acrylic acid-based copolymers); 0.1 and 5.3 (for copolymers of 4-vinylpyridine), and 19.7 and 34.4 (for poly(2- N,N-dimethylaminoethyl) methacrylate) mg metal ions per gram of polymer carrier, respectively. An attempt was made to evaluate the structure of the Fe-containing polymeric materials by Moessbauer spectroscopy. The parameters of the Moessbauer spectra such as the isomer shift, quadrupole splitting, effective internal magnetic field, and relative weight of the partial components were consequently determined for the complexes studied at different temperatures. The results obtained proved the existence of high-spin Fe3+ ions in oxygen- or nitrogen-containing ligand environment. [ABSTRACT FROM AUTHOR]

Abstract: La3Fe2− δ S7 (δ=0.042(6)) was synthesized through a reaction of the elements in a LiCl/KCl flux at 970K, and its structure was determined by single-crystal X-ray diffraction. The compound crystallizes in the polar hexagonal space group P63 with a=10.1906(6), c=5.9543(4)Å and Z=2, and adopts the Ce6Al10/3S14 structure type. The structure contains both octahedral and tetrahedral iron sites: one-dimensional rods of face-sharing FeS6 octahedra run along the 63 screw axis of the cell; FeS4 tetrahedra, all pointing in the same direction, are stacked along the threefold rotation axes. The iron-centered polyhedra are linked by lanthanum atoms, which are coordinated by [7+1] sulfur atoms in a bicapped trigonal prismatic arrangement. 57Fe Mößbauer spectroscopy confirms that FeIII and FeII cations occupy the tetrahedral and octahedral iron sites, respectively. Magnetic susceptibility data indicate an antiferromagnetic transition at T N≈155K. Density functional band structure calculations within the local density approximation reveal two covalent Fe–S subsystems within the compound that mix only weakly. A large anisotropy is indicated by bands that disperse predominantly along the hexagonal axis. The electronic band structure suggests pseudo-one-dimensional metallic conductivity along the rods of face-sharing FeS6 octahedra. However, due to the defects on the FeII positions, La3Fe2− δ S7 shows an activated conducting behavior. [Copyright &y& Elsevier]

Abstract: Structural, electronic and transport properties of LFN (LaFe1−z Ni z O3) and LSCFN (La1−x Sr x Co1−y −z Fe y Ni z O3) perovskites synthesized by a modified citric acid method were studied. Structure of the samples was characterized by X-ray studies with Rietveld method analysis. Magnetic properties and valence states of iron ions were characterized by 57Fe Moessbauer spectroscopy performed at RT, which were found to be greatly dependent on the chemical composition of the samples. Electrical conductivity was measured in the 20–800 °C temperature range and for some compositions relatively high values (exceeding 100 S cm−1) were observed in the 600–800 °C range. Chemical stability studies in relation to Ce0.8Gd0.2O1.9 electrolyte, performed for selected perovskite samples, revealed decreasing stability with increasing Ni concentration and formation of solid solutions in CGO/perovskite composites. The coefficient of thermal expansion (CTE) of LFN perovskites was found to match that of CGO electrolyte (CTE in the 10–13·10−6 K−1 range). [Copyright &y& Elsevier]

Abstract: Magnetic properties and hyperfine interactions of LaFe13− x Si x intermetallic compounds with large magnetic entropy changes were investigated by means of Mössbauer spectroscopy, band structure calculation and magnetization measurements. It was found that the 57Fe magnetic hyperfine field at FeI (8b) site is larger than that at the FeII (96i) site, whereas the magnetic moment of Fe atoms at the FeI site is smaller than that of Fe atoms at the FeII site. The temperature dependence of the average 57Fe magnetic hyperfine field was found to deviate from the mean field model close to T C, implying that the first-order magnetic phase transition is predominant in the sample of LaFe11.7Si1.3, and consequently results in a large magnetic entropy change. Furthermore, the effect of Si substitution for Fe on hyperfine parameters was investigated. [Copyright &y& Elsevier]

Abstract: Mixed copper and iron modified MCM-41 mesoporous silica with various Cu/Fe ratio are characterized by N2 physisorption, X-ray diffraction (XRD), transmission electron micrographs (TEM), X-ray photoelectron spectroscopy (XPS), Moessbauer spectroscopy and temperature programmed reduction with hydrogen. Their catalytic properties in methanol decomposition to CO and H2 are investigated and compared with that of the corresponding mono-component materials. The catalytic behaviour of bi-component materials are discussed based on the nature of the catalytic active sites. [Copyright &y& Elsevier]

Abstract: Nanosized iron oxide particles within various ordered mesoporous silicas (SBA-15, SBA-16, Fm3m, Ia3d) have been prepared from the corresponding nitrate and acetylacetonate precursors. N2 physisorption, X-ray diffraction and Moessbauer spectroscopy are used for their characterization. The reductive properties of the modified materials were investigated by temperature-programmed reduction with hydrogen. Methanol decomposition to H2, CO and methane was used as a test reaction. Some differences in the iron state, its phase transformations in reductive medium and also some variations in its catalytic behavior were observed and discussed in view of the iron oxide particle size dispersion and its dependency on the pore geometries of the silica supports. [Copyright &y& Elsevier]

Abstract: Series of iron oxide supported on CMK-1 and CMK-3 materials obtained by impregnation from aqueous or organic media are studied by TPR, XAFS, Moessbauer spectroscopy and methanol decomposition as a catalytic test. More highly dispersed iron oxide particles are obtained using ethanolic impregnation medium, but their dispersion is affected to a low extent by the support pore structure. On the basis of the combined results on the state and reductive phase transformations of the loaded iron oxide particles, more accessible CMK-3 in comparison with CMK-1 pore structure is assumed. [Copyright &y& Elsevier]

Abstract: Iron–cobalt spinel oxide nanoparticles with different Fe/Co ratios have been prepared by the combination of chemical precipitation with simultaneous ultrasonic treatment and subsequent mechanical milling. For comparison, their analogues obtained by thermal synthesis were also studied. Phase composition and structural properties of iron–cobalt oxides are investigated by X-ray diffraction and Moessbauer spectroscopy. Their catalytic behavior in methanol decomposition to CO and methane is tested. A well-defined effect of the preparation method and Fe/Co ratio on the reduction and catalytic properties of iron–cobalt samples is established. [Copyright &y& Elsevier]

Sr2/3La1/3FeO3 is a perovskite-type oxide with formally 67% Fe4+ and 33% Fe3+ ions revealing a charge disproportionation of Fe4+ and concomitant Fe3+Fe3+Fe5+ charge ordering below its Ne´el temperature of ∼200 K. Co-doped materials Sr2/3La1/3Fe1−xCoxO3 (0.15&les;x&les;0.33) were synthesized and investigated by X-ray powder diffraction, 57Fe Mo¨ssbauer spectroscopy, magnetization measurements, and magnetotransport studies in order to explore the relation between charge ordering, magnetic properties, and magnetoresistance effects in this system. Cobalt substitution induces the formation of charge disordered ferromagnetic clusters (x=0.15, 0.24) and finally leads to complete suppression of the charge disproportionation (x=0.33). Spin-glass like magnetic properties are observed. Pronounced negative magnetoresistance effects up to −20% at 5 K and 7 T are attributed to reduced scattering of charge carriers due to parallel spin alignment of ferromagnetic regions in an applied magnetic field. [Copyright &y& Elsevier]

The Moessbauer method was applied to obtain information on a suggested hydrogen bond in tobacco mosaic virus (TMV), between the hydroxyl group of Tyr 139 and a carboxyl oxygen of Glu 22 in a neighbouring subunit. Spectra of I were taken of 3,5-di-iodo- l-tyrosine as a free amino acid and in situ in TMV. The increase of the pK value of 3,5-di-iodo- l-tyrosine by 0.8 units at position 139 in TMV compared to the free value is a strong argument in favour of the existence of a hydrogen bond via the relevant hydroxyl group. The reported study demonstrates the surprising sensitivity of the observable Moessbauer parameters to details of the electronic configuration in the neighbourhood of the probe nucleus. [ABSTRACT FROM AUTHOR]

Abstract: The analysis of interatomic distances in complex transition metal chalcogenides of type A m [T n S p ] (A, alkali or alkaline earth metal; T, mainly Fe, Cu) can furnish interesting information on the oxidation state of the metal and also of sulfur. The charge distribution in complex anions can be estimated. Structural problems of the accommodation of the cations in framework structures leading to disorder can be detected. [Copyright &y& Elsevier]