Substitution of Fe(III) for Ga(III) in calcium gallate glass confirmed from the Debye temperature

A Debye temperature θ_D of 378 (±5K) has been obtained by applying a simplified Debye model to the⁵⁷Fe Mössbauer spectra of 60CaO·39Ga₂O₃·⁵⁷Fe₂O₃ glass. The θ_D value is comparable to those (280–580 K) obtained so far in several oxide glasses, glass-ceramics, and ceramics in which Mössbauer atoms are covalently bonded to oxygen atoms and play a role of network former. It proves that Fe(III) atoms occupy the substitutional sites of Ga(III) constituting distorted GaO₄ tetrahedra.     

Mössbauer spectroscopic study of γ-ray irradiated potassium borate glasses

Potassium borate glasses denoted by the formula xK₂O · (100 ? x)B₂O₃ · 7Fe₂O₃ were irradiated with ⁶⁰Co-γ-rays at room temperature. Mössbauer parameters for the irradiated glasses containing alkali equal to or higher than 20 mole% showed that the s-electron density at the iron nucleus increased without any change of the steric configuration of oxygen atoms around the iron nucleus. The increase of s-electron density was ascribed to electron transfer from the nonbridging oxygen to the iron nucleus. The presence of the nonbridging oxygen was also confirmed by the irradiation effect of the borate glass (x = 30) prepared using the enriched isotope of ⁵⁷Fe₂O₃. Mössbauer parameters for the irradiated glass suggest that the newly observed Fe²⁺ ions are in tetrahedral symmetry.     

Mössbauer and X-ray photoelectron spectroscopic studies of prussian blue and its related compounds

The ⁵⁷Fe Mössbauer spectra of three isomorphous compounds of the type Fe₄[M^B(CN)₆]₃ · xH₂O, where M^B is Fe, Ru or Os, have been measured in the temperature range between ?178 and 25°C. The spectral pattern of the ruthenium and osmium compounds is very similar to that of selectively enriched ⁵⁷Fe₄[Fe(CN)₆]₃ · xH₂O. The temperature dependence of the isomer shift and quadrupole splitting is interpreted in terms of lattice dynamics. The X-ray photoelectron spectra also support the conclusions drawn from the Mössbauer study.     

Crystal structure and magnetic properties of tris(2-hydroxymethyl-4-oxo-4H-pyran- 5-olato-κ2O5,O4)iron(III)

Tris(2-hydroxymethyl-4-oxo-4H-pyran-5-olato-κ²O⁵,O⁴)iron(III) [Fe(ka)₃], has been characterised by magnetic susceptibility measurements Mössbauer and EPR spectroscopy. The crystal structure of [Fe(ka)₃] has been determined by powder X-ray diffraction analysis. Magnetic susceptibility and EPR measurements indicated a paramagnetic high-spin iron centre. Mössbauer spectra revealed the presence of magnetic hyperfine interactions that are temperature-independent down to 4.2?K. The interionic Fe³⁺ distance of 7.31?Å suggests spin-spin relaxation as the origin of these interactions.     

Correlation of Mössbauer and Radiochemical Data on Hexacyanoferrate(III)

Mössbauer spectra of irradiated K₁Fe(CN)₆, observed 3 weeks after irradiation, showed that 3% of iron was converted to Fe(CN)₆^4?, while chemical analysis performed 100 hours after irradiation showed 18% was reduced to Fe(CN)₆^4?, Prussian blue was isolated in the chemical analysis, but not observed in the Mössbauer spectra. The Prussian blue formation was found to be time dependent.     

Mössbauer effect studies on alkali tris(maleato) ferrates(III)

Mössbauer spectra of alkali tris(maleato) ferrates(III), i.e., M₃[Fe(C₂H₂C₂O₄)₃]·nH₂O [M=Li, Na, K, Cs] at 300 K display a doublet. The Mössbauer parameters indicate these complexes to be high spin with octahedral symmetry. The isomer shift shows a decreasing trend with the increase in electronegativity/polarizing power of the substituent cation (Li⁺, Na⁺, K⁺, Cs⁺). A linear correlation between isomer shift values and the (Fe?O) stretching frequencies has also been observed.     

Improving the visible-light photocatalytic activity of SnO<Subscript>x</Subscript>·SiO<Subscript>2</Subscript> glass systems by introducing SnO<Subscript>x</Subscript> nanoparticles

Tin silicate glass without SnO_x nanoparticles (SiO₂·SnO_x), a silica glass containing only SnO_x nanoparticles (SiO₂·SnO_xNP) and the improved product, which combines the tin silicate glass with SnO_x nanoparticles (SiO₂·SnO_x·SnO_xNP) was prepared. For the structural analysis ¹¹⁹Sn Mössbauer spectroscopy and X-ray diffraction were applied. The ¹¹⁹Sn Mössbauer spectra showed that the SiO₂·SnO_x·SnO_xNP sample had the largest Sn^II content (12.0%). It also had an outstanding methylene blue degradation with the first-order rate value with (18?±?2) × 10^?3 min^?1 with visible light irradiation.     

Mössbauer and thermogravimetric study of ferrous gluconate

Ferrous gluconate Fe(C₆H₁₁O₇)₂·2H₂O was investigated by means of⁵⁷Fe (14.4 keV)-Mössbauer spectroscopy and thermogravimetry. The Mössbauer study was performed in the temperature range 80 to 423 K. It was found that Fe²⁺ occupies two distinctly different Mössbauer sites in the hydrated phase and a single site in the product of the thermal treatment. All samples were contaminated by some amount of Fe³⁺. A significant oxidation occurs during thermal treatment (about 378 K) at least for the samples exposed to the air. No Goldanskii-Karyagin effect has been detected, in contrast to the previous claim. It has to be noted that the ferrous gluconate is often used as the iron containing component of drugs used in the treatment of anaemia.     

Crystal structure and the magnetic properties of tris(2-chloromethyl-4-oxo-4H-pyran-5-olato-κ2O5,O4)iron(III)

The tris(2-chloromethyl-4-oxo-4H-pyran-5-olato-κ²O⁵,O⁴)iron(III), [Fe(kaCl)₃], has been synthesized and characterized by the crystal structure analysis, magnetic susceptibility measurements, Mössbauer, and EPR spectroscopic methods. The X-ray single crystal analysis of [Fe(kaCl)₃] revealed a mer isomer. The magnetic susceptibility measurements indicated the paramagnetic character in the temperature range of 2 K–298 K. The EPR and Mössbauer spectroscopy confirmed the presence of an iron center in a high-spin state. Additionally, the temperature-independent Mössbauer magnetic hyperfine interactions were observed down to 77 K. These interactions may result from spin–spin relaxation due to the interionic Fe³⁺ distances of 7.386 Å.     

MACROBICYCLIC D-METAL TRIS-DIOXIMATES OBTAINED BY CROSS-LINKING WITH P-BLOCK ELEMENTS. PART VI. PREPARATION,MOLECULAR STRUCTURE AND MÖSSBAUER (57FE, 119SN) PARAMETERS OF AN IRON(II) COMPLEX WITH A MACROBICYCLIC TIN-CONTAINING TRIS-NIOXIMATE LIGAND

Abstract

The tin-containing clathrochelate complex of Fe(II) with cyclohexanedione-1,2-dioxime (nioxime, H₂Nx), [FeNx₃(SnCl₃)₂]^2- · (Et₂NH⁺ ₂)₂ · Et₂NH₂ ⁺ · Cl^? · 2Prⁱ OH was prepared by slowly adding diethylamine to a solution containing the macrobicyclic [FeNx₃(SnCl₃)₂]^2- anion. The structure of the complex has been determined by X-ray methods. Crystal data: monoclinic, space group P2₁/c, a = 10.565(2), b = 25.413(5), c = 20.198(4)Å, β=95.40(3)°, Z = 4. The iron atoms is encapsulated by the clathrochelate ligand and surrounded by a distorted trigonal antiprismatic coordination sphere comprising by six nitrogen atoms of three dioxime residues. The experimental value of the distortion angle (ca 37.5°) is close to that predicted by the Mössbauer (⁵⁷Fe) parameters (ca 40°). The average Fe-N bond length of 1.923Å is somewhat greater than that in boron-containing analogues. The Sn atoms have a slightly distorted octahedral coordination, which also correspond to Mössbauer (¹¹⁹Sn) spectroscopic data. The six-membered carbocycles in the dioxime fragments have a half-chair conformation with both β-carbons displaced to the opposite sides of the mid-plane of the remaining atoms. All the active hydrogen atoms of the structure are involved in a hydrogen bond system.

The possibilities of use of Mössbauer parameters and their temperature dependences to determine the geometry of iron(II) tris-dioximates and the sign of Δ in Mössbauer (⁵⁷Fe) spectra are discussed.     

Anomalous spin state of iron(II) in 57Fe Mössbauer emission spectra of 57Co-Labeled tris(2-methylphenanthroline) cobalt(II) perchlorate

⁵⁷Fe Mössbauer emission spectra of the ⁵⁷Co labeled complex compound [⁵⁷Co(2-CH₃-phen)₃] (ClO₄)₂·2H₂O have been measured as a function of temperature between 293 and 4.6 K. The spectra exclusively show high-spin iron(II) resonances beside a small fraction of an high-spin iron(II) species, whereas the corresponding iron(II) compound is known to exhibit thermally induced high-spin ⁵T_2g(O_h) ? low spin ¹A_1g(O_h) transition. The electronic nature of the anomalous spin state has been found to be ⁵A₁(D₃) by a theoretical treatment of the temperature dependence of the quadrupole splitting. The results are in good agreement with those obtained from Mössbauer absorption measurements on [⁵⁷Fe_0.01Co_0.99(2-CH₃-(phen)₃] (ClO₄)₂·2H₂O.     

Mössbauer study of (Bi,Pb)-2223 superconductors irradiated with 86Kr ions

⁵⁷Fe Mössbauer spectroscopy was used to study the effects of heavy ion irradiation on (Bi_0.93Pb_0.17)Sr_1.9Ca_2.05(Cu_1.02Fe_0.01)₃O_y superconductors. The Mössbauer spectra of the irradiated superconductor showed significant changes in the subspectra belonging to different Cu microenvironments into which Fe ions were substituted. The relative occurrence of Fe occupying the square pyramidal fivefold oxygen coordinated Cu sites decreased while Fe^{3 +} substituting the square planar fourfold oxygen coordinated Cu sites increased upon bombardment by 246 MeV ⁸⁶Kr⁸⁺ ions. This observation was interpreted on the basis of partial replacement of the apical oxygen atoms in the square pyramids surrounding one of the Cu sites. Such oxygen vacancies create additional square planar coordination sites for Cu. These results also support the covalent character of Cu-O bonds in the superconducting layer as well as the ionic character of bond of apical oxygen to Cu.     

Structural investigation of the EuBa2Cu3O7-δ high TC superconductor by 151Eu, 119Sn, 57Fe and 57Co Mössbauer spectroscopy

By introducing ¹⁵¹Eu, ¹¹⁹Sn, ⁵⁷Fe and ⁵⁷Co into the orthorhombic perovskite lattice of YBa₂Cu₃O_7-δ high T_C superconductors, the localization and distribution of these probe nuclides were investigated by Mössbauer spectroscopy in order to get further information on the structure of high T_C superconductors. The Mössbauer spectra of superconductor samples were considered as superpositions of subspectra belonging to Mössbauer nuclides occupying different sites with various surroundings in the lattice. The ¹⁵¹Eu spectra were evaluated as singlets corresponding to Eu^III situated at the normal rare earth site. The ¹¹⁹Sn spectra were decomposed into a singlet and a doublet, which were associated with Sn^IV at the Cu(2) and the Cu(1) sites, respectively. The ⁵⁷Fe and ⁵⁷Co spectra could be fitted with three doublets representing Fe^III and Fe^IV at the Cu(1) site as well as Fe^III at the Cu(2) site. Comparing the relative area fractions of Mössbauer lines corresponding to different Cu sites it was suggested that iron and cobalt prefer the Cu(1) site, while tin prefers the Cu(2) site in these superconductors.     

Mössbauer study on the crystallization of IR-transmitting aluminate glasses

Heat treatment of 60CaO·10BaO·17Al₂O₃·13Fe₂O₃ glass causes a precipitation of the nanoparticles of antiferromagnetic Ca₂Fe₂O₅ and ferromagnetic BaFe₂O₄. Mössbauer spectra of these glass-ceramics show a magnetic relaxation spectra superimposed on doublets. A Kissinger plot in the DTA method reveals that simultaneous cleavage of Ca-O and Fe-O bonds and that of Ba-O and Fe-O bonds cause the precipitation of Ca₂Fe₂O₅ and BaFe₂O₄, respectively. Introduction of Fe(III) promotes the crystallization of aluminate glass. In the case of iron-free 60CaO·10BaO·30Al₂O₃ glass, Ca₂Al₂O₅ and BaAl₂O₄ particles precipitate instead of Ca₂Fe₂O₅ and BaFe₂O₄ particles, respectively.     

On the spin relaxation of57Fe(III) species produced through EC-decay in diamagnetic57Co-labelled Co(III) compounds

Absorption Mössbauer spectra of high-spin⁵⁷Fe(acac)₃ incorporated in diamagnetic Co(acac)₃ and in paramagnetic Mn(acac)₃ and of the γ-ray irradiated (⁵⁷Fe, Co) (acac)₃ and (⁵⁷Fe, Mn) (acac)₃ were compared with emission spectra of⁵⁷Co-labelled Co(acac)₃. Magnetic hfs is found in the spectra of (⁵⁷Fe, Co) (acac)₃ at 78 to 195 K, whereas such hfs is observed neither for the spectrum of⁵⁷Co-labelled Co(acac)₃ nor for that of γ-ray irradiated (⁵⁷Fe, Co) (acac)₃). The absence of magnetic hfs in the spectrum of diamagnetic⁵⁷Co-labelled cobalt(III) compounds was ascribed to the spin-spin interaction due to the radicals produced in the vicinity of the decayed atom.     

Catalytic conversions of chloroolefines over iron oxide nanoparticles 3. Electronic and magnetic properties of γ-Fe2O3 nanoparticles immobilized on different silicas

Catalytic properties of superparamagnetic γ-ferric oxide nanoclusters, which are uniform in terms of size and magnetic properties were studied. The catalysts were supported on the activated silica gel matrix (AGM) prepared from the KSK-2 silica gel of globular structure and on the activated silica matrix (ASM) prepared from layered natural vermiculite. The clusters are active in some reactions of chloroolefin conversions: isomerization of dichlorobutenes and alkylation of benzene with allyl chloride. Their activity in these reactions is many times higher that of usual supported catalysts based on α-ferric oxide. Analysis of the Mössbauer spectra of the 2.5 wt.% Fe/AGM and 2.5 wt.%Fe/ASM samples before and after the reaction at T = 3–300 K shows that during the reaction some Fe^III ions arranged in ～2–3-nm γ-Fe₂O₃ nanoclusters magnetically ordered at 6 K are reduced to form a high-spin Fe^II complex in the paramagnetic state. According to the macroscopic magnetization data (SQUID) of the initial clusters, curves with hysteresis are observed at 2 K in the plots of forward and backward magnetization, while the 2.5 wt.%Fe/ASM catalyst after the reaction at T = 2 K demonstrates a linear field dependence of the magnetization passing through the coordinate origin. Analysis of the Mössbauer spectra and magnetic properties suggests that during the catalytic reaction the Fe^III ions in the γ-Fe₂O₃ nanoclusters interact with chloroolefin with the allylic structure to be partially reduced to the Fe^II ions that are bound in a complex containing chloride ions and O^II ion(s) of the silicate matrix as ligands. This is a reason, probably, for the high catalytic activity of γ-Fe₂O₃ nanoparticles.     

Determination of the electric field gradient tensor in sodium nitroprusside using a polarized Mössbauer source

The orientation of the electric field gradient tensor at the iron nucleus in a single crystal of Na₂[Fe(CN)₅(NO)]·2H₂O has been determined using a polarized Mössbauer source of ⁵⁷Co in iron metal.     

Mössbauer Studies on Spin Crossover in Schiff Bases Complexes of Iron (III)

The Mössbauer spectra of the imidazole adducts of tetradentate Schiff bases complexes of Iron (III), (FeLIm₂)⁺ have been measured. Based on the Mössbauer spectra and magnetic moments, the spin-equilibrium of Low-spin ? high-spin for [Fe(bzacen)(lm)₂)B(ph)₄ was observed.     

On the lack of capillary Mössbauer spectroscopic effect for SnII-containing aqueous solutions trapped in corning Vycor ‘thirsty’ glass

Liquids trapped in the pores of certain silicate glasses (such as Corning Vycor ‘thirsty’ glass) were found to display frozen solutions like behavior at temperatures much higher than their actual freezing point. For example, recoilless γ-resonance absorption was observed for Mössbauer active solutes such as ¹¹⁹Sn and ⁵⁷Fe salts at room temperature (i.e., without the need of quenching). Thus capillary Mössbauer spectroscopy (CMS) proved to be a new and useful experimental tool with great potential in solution chemistry. As part of a research project concerned with the hydrolysis of Sn^II salts, we attempted to perform ¹¹⁹Sn CMS measurements for solutions containing stannous ion in a range of aqueous environments. Somewhat surprisingly, we found that under ambient conditions, Sn^II aqueous liquid solutions, both the acidic and the basic systems, are essentially CMS-silent. This can be attributed to the strong temperature dependence of Lamb–Mössbauer factor of Sn^II species, which may result in the complete disappearance of Mössbauer pattern well below room temperature. These observations can also explain why previous publications concerned with the use of CMS dealt exclusively with Sn^IV and not with Sn^II containing liquids.     

Mössbauer Spectroscopic Studies of Supported α-Fe2O3 and Fe Catalysts II: The Effect of the Second Metal Addition

The effect of the addition of a second metals such as Zn and Ni on the calcinaton and reduction of alumina, magnesia and silicasupported iron catalysis with total iron loading of 5wt% is investigated by Mössbauer spectroscopy. It is shown that the reducibility of supported α-Fe₂O₃ is gradually increased by adding the second metal. The values of the magnetic hyperfine field obtained from Mössbauer spectra for the Zn or Ni-added α-Fe₂O₃ or Fe catalysts decreased with increasing second metal loading.