Molecular orbital calculation of Mössbauer parameters for Fe(CO)4 (C2H4) in low temperature matrix

Molecular orbital calculations have been performed to obtain the electron density and electric field gradient at the iron nucleus of tetracarbonylethene iron Fe(CO)₄(C₂H₄) produced by UV-irradiation of pentacarbonyliron cocondensed homogeneously with ethene in a low temperature matrix, so as to estimate the Mössbauer parameters of the species. Mössbauer isomer shifts and electron densities at iron nuclei (O) of Fe(CO)_n (n=5,4,3,2) as well as Fe(CO)₄(C₂H₄) are discussed: they have fairly good linear relationship to give –0.27 mm/s/a_O ^–3. An isomer of Fe(CO)₄(C₂H₄) produced via thermal reactions of Fe(CO)₄ with ethene in a stratified matrix is discussed by comparing the calculated and observed Mössbauer parameters.     

Characterization of a few Mexican clays

The characterization of a few Mexican clays with chemical treatmentfor possible application as catalysers is shown. The natural clays are treatedwith H₂ SO₄ , HF, F₃ CSO₃ H, ClSO₃ H, HClO₄ and their behavior in reactions with some alcoholswas recorded. The analysis were made before and after using the clays as catalysers.The clays were characterized by Mössbauer spectroscopy, X-ray diffraction,X-ray fluorescence analysis, and differential thermo analysis. The predominantmineral species are: montmorillonite, christobalite and quartz. The main elementsare: Si, Al, Fe, Ca, K, etc. The Mössbauer results show mainly a paramagneticdoublet of Fe₃₊ . The clays behave similarly as described in theliterature.     

57Fe Mössbauer spectroscopic characterisation of a ferromanganese nodule from the Central Indian Ocean

The iron bearing phases present in a ferromanganese nodule from the Central Indian Ocean have been determined using⁵⁷Fe Mössbauer spectroscopy. The Mössbauer results have been corroborated by XRD, IR and TG-DTA studies. The Mössbauer spectrum of a ferromanganese nodule shows a broad line width which indicates the presence of more than one iron bearing paramagnetic oxide or oxyhydroxide phases where iron is present as Fe³⁺. -FeOOH has been distinctly characterised as one of the iron bearing phases in the nodule. Other oxyhydroxide and oxide phases of iron in the nodule have been ruled out. A typical paramagnetic doublet persists even at very high temperature which has been proposed to be due to iron(III)phosphate. Formation of solid solution of Mn₂O₃–Fe₂O₃ has been observed in the heat treated nodule at 1073 K, which has been characterised by the Mössbauer technique.     

Mössbauer study of hydrogenated Fe-Zr amorphous alloys

The effect of electrochemical hydrogenation was investigated in Fe₉₀Zr₁₀ and Fe₈₉Zr₁₁ amorphous alloys by means of⁵⁷Fe Mössbauer spectroscopy. Significant changes in the Mössbauer spectra as well as in the hyperfine field distribution of hydrogenated samples were found with increasing hydrogen concentration. It was established that the dependence of Curie temperature on hydrogen content had a maximum, and the hydrogen had two mean localization sites. By comparing the Mössbauer spectra of hydrogenated samples as-quenched and annealed before hydrogenation it was shown that low-temperature relaxation processes were going on at aging temperature as low as 150°C in this amorphous alloy and the low-temperature relaxation processes modify the localization of hydrogen. The combination of the hydrogenation and Mössbauer techniques gives a very sensitive method for detecting structural changes.     

Molecular orbital calculation of Mössbauer parameters for tin compounds in low temperature matrices

Mössbauer parameters of tin compounds, Sn(CH₃)_nCl_4–n (n=0, 1, 2, 3, 4), isolated in low temperature matrices are correlated with electronic properties at the tin nuclei obtained by molecular orbital calculations. The Mössbauer isomer shift and quadrupole splitting show good correlation with electron density and electric field gradient estimated by molecular orbital calculations, respectively. Structures of novel species (Sn(CH₃)₂CH₂ and [Sn(CH₃)₂CH₂]₂) produced via photodissociation of Sn(CH₃)₄ in low temperature matrices were estimated by means of molecular orbital calculations as compared with Mössbauer parameters.     

Molecular orbital calculation of Mössbauer parameters for Sn(CH3)nH4−n (n=0, 1, 2, 3) and their photoproducts in low temperature matrices

Mössbauer parameters of tin compounds, Sn(CH₃)₂H_4–n (n=0, 1, 2, 3, 4), isolated in low temperature matrices were related to electronic properties at the tin nuclei obtained by molecular orbital calculations. Structures of novel species, Sn(CH₃)₂ and Sn(CH₃)H, produced via photodissociation of matrix-isolated Sn(CH₃)₃H and Sn(CH₃)₂H₂, respectively, were determined on the basis of molecular orbital calculations as compared with Mössbauer parameters. The correlations between Mössbauer quadrupole splitting and calculated electric field gradient using STO-3G or MINI-4 were found to depend on the valence of tin atoms because of poor allowance for basis sets in describing highly polar molecules.     

Mössbauer study on the photochemical reactions of pentacarbonyliron with ethene in low temperature nitrogen matrix

The UV-induced photochemical reactions of pentacarbonyliron with ethene in a low temperature nitrogen matrix were studied by means of the Mössbauer technique. Fe/CO/₄/C₂H₄/ was produced by UV-irradiation of penfacarbonyliron in close proximity to ethene molecules in a pure ethene matrix, or a homogeneous cocondensed matrix. The other products were obtained via thermal reactions with ethene of Fe/CO/₄ trapped in stratified matrices.     

Studies on InFeMO4 (M=Mg, Co, Ni, Cu and Zn) compounds: Crystal structure and cation distribution

The crystal structure and the cation distribution in a series of InFeMO₄ compounds (M=Mg, Co, Ni, Cu and Zn) have been studied by means of X-ray powder diffraction and ⁵⁷Fe Mössbauer spectroscopy. The M=Mg, Co and Ni samples were confirmed to crystallize with the cubic spinel structure (space group Fd-3m), whereas the M=Cu and Zn samples adopted a hexagonal structure. For all the phases, the cation stoichiometry was found to deviate from the ideal molecular formula, InFeMO₄. The paramagnetic Mössbauer spectra of the samples were analyzed using a four-component fitting model suggested by a statistical simulation with point-charge calculation. The Mössbauer data confirmed the trivalent state for iron at both cation sites in all samples. The results from the fitting of the Mössbauer spectra were also employed in Rietveld refinement of the X-ray diffraction data for the determination of exact cation distribution. It was seen that the distribution of Fe at the A and B sites follows very closely the 1:2 ratio of the ideal formula AB₂O₄ for all samples, whereas trivalent indium was clearly seen to favor the A site and divalent M cation the B site.     

Mössbauer study on the photolysis of pentacarbonyliron isolated in low temperature nitrogen matrix by continuous or pulsed deposition

The UV photolysis of pentacarbonyliron isolated in low temperature nitrogen matrix by continuous or pulsed deposition was studied by means of Mössbauer technique. Unstable species such as Fe/CO/_n /n=2–4/ were produced by UV irradiation and their Mössbauer parameters were measured. The yields of unstable species were found to be influenced by the deposition method of nitrogen matrix.     

Determination of α and f for k0-NAA in irradiation sites with high thermalized neutrons

We have measured the ⁵⁷Fe Mössbauer spectra of the Hofmann pyridine complex Fe(pyridine)₂Ni(CN)₄ sample before and after exposure to high pressure of gaseous xenon. The temperature dependence of the high spin molar fraction has been determined from the ⁵⁷Fe Mössbauer spectra. The spin transition of the sample without the high pressure treatment occurs between 175 and 220 K with a hysteresis width of 15 K. Although the ⁵⁷Fe Mössbauer spectra suggest that the spin crossover behavior of the sample before and after the high pressure treatment are almost the same, the hysteresis of the latter sample is somewhat larger.     

Thermal analysis of quinolinium tetrachloroferrate(III)

Thermal decomposition of a compound consisting of a tetrachloroferrate(III) anion and a quinolinium cation, of general formula [QH][FeCl₄], has been studied using TG-FTIR, TG-MS, DTA and DTG techniques. The measurements were carried out in an argon atmosphere over the temperature range 20-800 °C. The solid products of the thermal decomposition were identified by IR, FIR and Mössbauer spectroscopy.     

Thermal decomposition of iron(VI) oxides, K2FeO4 and BaFeO4, in an inert atmosphere

The thermal decomposition of solid samples of iron(VI) oxides, K₂FeO₄·0.088 H₂O (1) and BaFeO₄·0.25H₂O (2) in inert atmosphere has been examined using simultaneous thermogravimetry and differential thermal analysis (TG/DTA), in combination with in situ analysis of the evolved gases by online coupled mass spectrometer (EGA-MS). The final decomposition products were characterized by ⁵⁷Fe Mössbauer spectroscopy. Water molecules were released first, followed by a distinct decomposition step with endothermic DTA peak of 1 and 2 at 273 and 248 °C, respectively, corresponding to the evolution of molecular oxygen as confirmed by EGA-MS. The released amounts of O₂ were determined as 0.42 and 0.52 mol pro formula of 1 and 2, respectively. The decomposition product of K₂FeO₄ at 250 °C was determined as Fe(III) species in the form of KFeO₂. Formation of an amorphous mixture of superoxide, peroxide, and oxide of potassium may be other products of the thermal conversion of iron(VI) oxide 1 to account for less than expected released oxygen. The thermogravimetric and Mössbauer data suggest that barium iron perovskite with the intermediate valence state of iron (between III and IV) was the product of thermal decomposition of iron(VI) oxide 2.     

Iron-Iridium Mixed-Metal Carbonyl Clusters: A Mössbauer Study of the Structure and of the Adsorption of [Fe2Ir2(CO)12]2− on MgO

¹⁹³Ir and ⁵⁷Fe Mössbauer spectroscopy was used to investigate the structure of the [Fe₂Ir₂(CO)₁₂]^2- cluster compound and the adsorption of this cluster on hydrated MgO. Supported samples were prepared by impregnation of the magnesia with solutions of [Et₄N]₂[Fe₂Ir₂(CO)₁₂] in acetone. The Mössbauer and FT-IR spectra of the MgO-supported cluster confirm that the bimetallic carbonyl is molecularly physisorbed onto MgO without undergoing any transformation or decomposition. The easy solvent extraction of the intact cluster from the oxide surface excludes ion pairing between the cluster anion and the Mg²⁺ surface sites. Mössbauer spectra are in agreement with the refined structure of the molecular cluster and the temperature dependence of the ⁵⁷Fe Mössbauer spectra above 80 K is consistent with the low degree of interaction of the cluster with the support. This technique, therefore, appears to be promising in order to infer structural information when X-ray determination fails.     

Mösbauer chemical phase characterization of iron aerosols

⁵⁷Fe Mössbauer spectroscopy has been employed to characterize the chemical composition of iron aerosols collected from three distinct groups of sites representing remote, urban and industrially active areas. The Mössbauer spectra clearly show this environmental difference. The fact that the spectra of the samples collected from the remote areas are quite similar to those of clay minerals corroborates the view that iron aerosols are soil derived. Similarly the predominant presence of -Fe₂O₃ and Fe₃O₄ in the close vicinity of industrial activities suggests that the Mössbauer spectroscopy can help identify the anthropogenic processes against the natural ones.Work performed under the Punjab States Research Scheme NPC-5.     

Mössbauer, vibrational spectroscopic and solution X-ray diffraction studies of the structure of iron(III) complexes formed with indole-3-alkanoic acids in acidic aqueous solutions

The chemical reactions between iron(III) and indole-3-acetic (IAA), -propionic (IPA), and -butyric (IBA) acids were studied in acidic aqueous solutions. The motivation of this work was that IAA is one of the most powerful natural plant-growth-regulating substances (phytohormones of the auxin series). Mössbauer spectra of the frozen aqueous solutions of iron(III) with indole-3-alkanoic acids as ligands (L), showed parallel reactions between Fe³⁺ and the ligands. Partly, it resulted in a complex formation which precipitated in aqueous solution and partly, in a redox process with iron(II) and the oxidised indole-3-alkanoic acids as products. The Mössbauer parameters of the Fe²⁺ species suggested a hexaaquo coordination environment. The chemical composition and coordination structure of the precipitated complexes were investigated using elemental analysis, Mössbauer spectroscopy, Fourier transform infrared (FTIR) and Raman spectroscopic techniques. The complexes were soluble in some organic solvents. So, Mössbauer, FTIR and solution X-ray diffraction measurements were carried out on the solution of complexes in acetone, hexadeutero acetone and methanol, respectively. The data obtained supported the existence of the μ-dihydroxo-bridging structure of the dimer: [L₂Fe<(OH)₂>FeL₂] (where L is indole-3-propionate, -acetate or -butyrate).     

Mössbauer, vibrational and electronic spectroscopy of trinuclear μ-oxo iron(III) acetate clusters with pyridine and derivatives as ligands

In this study we have investigated eight complexes of the general composition [Fe₃O(OOCCH₃)₆(L)₃]NO₃, where L is a heterocyclic ligand, viz. a 4-substituted pyridine. The Mössbauer spectra of the complexes showed isomer shifts and quadrupole splittings that are characteristic of iron(III) high-spin complexes. The Mössbauer quadrupolar doublets showed asymmetries that are attributed principally to the Goldanskii-Karyagin effect. A correlation is proposed between the Mössbauer parameters, and between the energy of the charge transfer band spectra, and the pK_a values of the N-heterocyclic ligands.     

Mössbauer study of Al6 (Fe,Mn) formation in Al-rich Al−Fe−Mn alloys

Al–Fe–Mn alloys containing 0.5 wt. % iron and 0–3.0 wt. % manganese were prepared at different cooling rates from 0.1 to 500 K/s and studied by Mössbauer spectroscopy. Beyond the usual phase analysis, it was found that the presence of manganese is responsible for the decrease of the quadrupole splitting and isomer shift of the Al₆(Fe,Mn) phase, compared to those of Al₆Fe. It was also shown that the Mössbauer parameters are characteristic of the average manganese content of Al₆(Fe,Mn) only if there are no substantial fluctuations of the Fe/Mn ratio in the Al₆(Fe,Mn) phase. Accurate Mössbauer parameters for the Al₆Fe phase were also determined.     

Thermal decomposition and structural reconstruction effect on Mg-Fe-based hydrotalcite compounds

The thermal decomposition and structural reconstruction of Mg-Fe-based hydrotalcites (HT) have been studied through thermogravimetric analyses, X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy and Mössbauer spectroscopy. The destruction of the layered structure took place at about 300°C. The broad peaks observed in the X-ray diffractograms suggest that the resultant oxides constitute a solid solution. For samples treated at temperatures higher than 500°C, the formation of the MgO and MgFe₂O₄ spinel phases is observed. ⁵⁷Fe Mössbauer spectroscopy was employed to monitor the Fe chemical environment for the samples annealed at different temperatures (100-900°C). In situ XRD experiments revealed that the HTs start an interlayer contraction at about 180°C. This phenomenon is identified as being due to a grafting process for which the interlamellar anions attach to the layers through a covalent bond. The reconstruction of the HTs was also investigated and its efficiency depends on the thermal annealing temperature and the Mg/Fe ratio. The structure of the reconstructed samples was found to be exactly the same as the parent structure.     

A119Sn-Mössbauer study of tetramethylstannane isolated in low temperature argon matrix

Unusually broad¹¹⁹Sn-Mössbauer absorption was observed in pure Sn(CH₃)₄ or Sn(CH₃)₄/argon condensed at low temperatures by pulsed deposition. Such broadening of the Mössbauer linewidth suggested the presence of large quadrupole splitting due to possible distortion of molecular structure as deposited in the argon matrix.     

Thermal decomposition of pyrite

Thermal decomposition of natural pyrite (cubic, FeS₂) has been investigated using X-ray diffraction and⁵⁷Fe Mössbauer spectroscopy. X-ray diffraction analysis of pyrite ore from different sources showed the presence of associated minerals, such as quartz, szomolnokite, stilbite or stellerite, micas and hematite. Hematite, maghemite and pyrrhotite were detected as thermal decomposition products of natural pyrite. The phase composition of the thermal decomposition products depends on the temperature, time of heating and starting size of pyrite crystals. Hematite is the end product of the thermal decomposition of natural pyrite.