Cubic β-Fe2O3 as the product of the thermal decomposition of Fe2(SO4)3

Hyperfine Interactions - The thermal decomposition of Fe2(SO4)3 in air has been investigated using transmission Mössbauer spectroscopy, CEMS and X-ray powder diffraction. The hexagonal...     

Mechanism of solid-state oxidation of FeSO4·H2O: model of simultaneous reactions

The mechanism of the thermal transformation of FeSO₄·H₂O in air has been studied under isothermal conditions at temperatures (150–460)°C using mainly⁵⁷Fe Mössbauer spectroscopy and X-ray powder diffraction (XRD). Two trends are typical for the thermal behaviour of FeSO₄·H₂O in air, a tendency toward oxidation and dehydration. We suggested a new transformation model consisting of two ways of oxidation, direct one and indirect one. Fe(OH)SO₄ was identified as a product of the direct way, Fe₂(SO₄)₃ and superparamagnetic nanoparticles ofγ-Fe₂O₃ as products of the indirect way. The suggested model of simultaneous reactions explains the unusual non-monotonous dependence of the oxidation level of the thermally treated samples on temperature.     

The Role of Intermediates in the Process of Red Ferric Pigment Manufacture from FeSO4⋅7H2O

One method of industrial manufacture of red ferric pigments is based on the thermal decomposition of FeSO₄7H₂O into -Fe₂O₃(copperas red). The difficult reproducibility of the color quality of the final pigment is the main problem of this process. One of the factors that can influence the pigment color is contamination by some of the intermediates formed during the transformation process. The identification of two groups of intermediates is the basic result of an extensive laboratory investigation carried out using ⁵⁷Fe Mössbauer spectroscopy and X-ray powder diffraction (XRD). The first group of intermediates includes sulfato-phases as FeSO₄H₂O, FeSO₄, Fe(OH)SO₄, Fe₂O(SO₄)₂, Fe₂O(SO₄)₂xH₂O x(0,1), and Fe₂(SO₄)₃. Thermally metastable polymorphs of iron(III) oxide, -Fe₂O₃, -Fe₂O₃ and -Fe₂O₃, represent the other group. Mössbauer characterization of all intermediate products is given. A significant influence of -Fe₂O₃ on the pigment color was found.     

On the origin of diastereoselectivity in [2 + 2 + 2] cycloisomerization of chiral triynes: controlling helicity of helicene-like compounds by thermodynamic factors

Diastereoselective CoI-mediated [2 + 2 + 2] cycloisomerization of CH(3)O-substituted optically pure aromatic triynes to obtain nonracemic functionalized helicene-like compounds (comprising a penta-, hexa-, and heptacyclic helical scaffold) was studied. The stereochemical outcome of the reaction at 140 degrees C using CpCo(CO)(2) was controlled by thermodynamic factors yielding diastereomeric ratios up to 91:9. Using CpCo(ethylene)(2) at room temperature, a kinetic control took place leading to the loss of stereoselectivity. Barriers to epimerization for selected helicene-like compounds were measured indicating their lower configurational stability in comparison to the parent carbohelicenes. Free energy differences between corresponding pairs of diastereomers (calculated at the DFT B3LYP/TZV+P level) were in excellent agreement with the experimental data and allowed for the prediction of the stereochemical outcome of the reaction. An optically pure hexacyclic helicene-like alcohol was prepared on a multigram scale. Its X-ray structure confirmed the previous helicity assignments being based on (1)H-(1)H correlations in ROESY (1)H NMR spectra.