Préparation et étude d'un oxysilicate de fer de valence mixte Fe7(SiO4)O6 (iscorite)

Un cristal de Fe₇SiO₁₀ a été isolé par J. Smuts, J. Steyn, et J. Boeyens (Acta Crystallogr. B25, 1251 (1969)), dans un réfractaire sidérurgique usagé, et appelé iscorite. Selon ces auteurs, la maille est monoclinique et la structure basée sur un empilement de blocs FeO et Fe₃SiO₆; mais le facteur d'accord est médiocre (R = 0,165) et les distances interatomiques très incorrectes. Nous avons donc préparé, pour la première fois, cette phase, et montré en combinant l'analyse chimique, la densité, l'étude aux rayons X du système FeSiO, et l'analyse d'un cristal à la microsonde, que la composition la plus correcte est Fe₇(Si_0.94Fe_0.06)O₁₀. L'étude d'un cristal confirme et précise la maille de Smuts et al.: monoclinique, avec a = 21,336(2), b = 3,0679(3), c = 5,8744(8)Å, β = 98°,06(1), $\text{P2}\text{m}$ ou $\text{P2}{}_1\text{m}$. Cependant les diagrammes de Weissenberg présentent des lignes continues de diffusion pour certaines strates qui indiquent un désordre microstructural intense. Il en va de même pour la diffraction des électrons. Il n'est donc pas étonnant que l'affinement, sur la base du modèle de Smuts et al., ait donnéR = 0,09 dans l'un ou l'autre groupe d'espace. Les mesures magnétiques conduisent à un paramagnétisme avec forte contribution orbitale pour Fe²⁺, et mise en ordre vers 250 K avec, en-dessous, un comportement de ferromagnétique faible. Contrairement à la wüstite, l'iscorite ne se dismute pas facilement; elle donne avec Fe₉PO₁₂ des solutions solides limitées.A crystal of Fe₇SiO₁₀ has been isolated by J. Smuts, J. Steyn, and J. Boeyens (Acta Crystallogr. B25, 1251 (1969)), from a furnace refractory brick, and has been called iscorite. According to these authors, the cell is monoclinic and the structure based upon a stacking of FeO and Fe₃SiO₆ blocks; however the reliability factor is poor (R = 0.165) and the interatomic calculated distances are not correct. Therefore, we have prepared this phase for the first time; combining chemical analysis, density measurements, X-ray investigation of the FeSiO system, and electron probe microanalysis of a crystal, we have shown that the correct composition is Fe₇(Si_0.94Fe_0.06)O₁₀. The crystal study confirms, with a higher accuracy, the parameters for the cell proposed by Smuts et al.: a = 21.336(2), b = 3.0679(3), c = 5.8744(8)Å, β = 98°.06(1), $\text{P2}\text{m}$ or $\text{P2}{}_1\text{m}$. However, the Weissenberg patterns display continuous diffusion lines, indicating an intense microstructural disorder, in agreement with the electron diffraction patterns. Hence it is not surprising to obtain, on the basis of the Smuts et al. model, a value R = 0.09 with both space groups. The magnetic measurements indicate a paramagnetism with strong orbital Fe²⁺ contribution and a transition at ～250 K to an ordered magnetic state, with a weak ferromagnetism below 250 K. In contrast to the case of wustite, iscorite does not easily disporportionate; it forms limited solid solutions with Fe₉PO₁₂.     

Fe3PO7, Un cas de coordinence 5 du fer trivalent,etude structurale et magnetique

The structure of Fe₃PO₇ is established from a single crystal. The cell is trigonal R3m, with, in hexagonal reference a = 8,006(5), c = 6,863(5)Å, Z = 3. The structure is determined with the direct method and refined to R = 0,027. The PO₄ tetraedra are isolated; the iron atoms are in a five coordinated site constituted of trigonal bipyramids sharing 2 edges and forming groups of 3 hexaedra; through these shared edges the iron atoms are at 3.13 Å a distance rather short which brings a repulsion causing the off centering of the cation along the pseudo axis of the bipyramid. The magnetic measurements and the Mössbauer spectroscopy show antiferromagnetism behaviour and, in the paramagnetic state, outstanding parameters (μ = 6.45 μ_B, θ_p = ?1707 K) recalling however Ca₂Fe₂O₅ or LaFeO₃. The Mössbauer spectroscopy gives, at room temperature, parameters classical for trivalent iron; through cooling, it points to a magnetic transition temperature of 160 ± 3 K below which the spectrum displays at least 2 hyperfine patterns. The magnetic interactions are discussed.     

Le phosphate de cobalt et de lithium à valence mixte Li4+xCo2−x(P2O7)2 (x = 0,03): étude structurale et analyse de distribution de charge

The title compound, namely lithium cobalt(II/III) bis(diphosphate), Li_4.03Co_1.97(P₂O₇)₂, is a new mixed‐valent lithium/cobalt(II/III) phosphate. Three metal sites out of seven are occupied simultaneously by Li⁺ and Co^II/III ions. This disorder was established both from an analysis of the atomic displacement ellipsoids and Li/Co—O bond distances, and by means of a charge‐distribution (CHARDI) model, which provides satisfactory agreement on the computed charges (Q) for all the cations.     

Proprietes magnétiques et étude par spectroscopie Mössbauer des tellurites de fer Fe2Te3O9 et Fe2Te4O11: Structure magnétique de Fe2Te4O11 à 4,2 K

Magnetic study and Mössbauer resonance measurements of the tellurites Fe₂Te₃O₉ and Fe₂Te₄O₁₁ characterize antiferromagnetic ordering. The transition temperatures determined by Mössbauer resonance, are 34 and 27 K, respectively. At 295 K the values of chemical shifts, 0.35 and 0.39 mm/sec, are typical of high-spin Fe(III) in octahedral coordination. Neutron powder diffraction was used to determine the magnetic structure of Fe₂Te₄O₁₁ at 4.2 K. It shows antiferromagnetic interactions between Fe³⁺ ions belonging to [Fe₂O₁₀] groups. The magnetic space group is $\text{P}{}_{\mathrm{2a}}\text{2}{}_1\text{c}$.     

L'oxyde double Fe2WO6. I. Structure cristalline et filiation structurale

The authors have found a new structural type, related to α-PbO₂, called tri-α-PbO₂. The oxide Fe₂WO₆ is the prototype. It crystallizes in the orthorhombic system with the following cell parameters: a = 4.576 Å, b = 16.766 Å, and c = 4.967Å. The space group is Pbcn. The structure has been determined by X-ray single-crystal methods and refined by least-squares procedures (R = 0.065).The structure consists of zig-zag chains parallel to the c-axis. Each such chain is built up by MO₆ (M = Fe or W) octahedra-sharing edges. The chains are linked together by corner sharing. There are two types of chains: one containing only iron atoms, the other being an ordered 1-1 arrangement of iron and tungsten atoms.     

Action de nucléophiles simples sur un bromoénurononitrile,précurseur et équivalent synthétique partiel d'un ynurononitrile

Reactions of Mononucleophiles with a Bromoenurononitrile, Precursor and Partial Synthetic Equivalent of an Ynurononitrile Several mononucleophiles (bases) have been reacted with one or the other of the geometrical isomers of the bromoenurononitrile 1. Depending on the nucleophile and the conditions, many different mechanistic pathways were followed, f. ex.: with OH^?, stereospecific elimination from (Z)- 1 leading to 2 , with N^?₃ and F^?, stereospecific E-A_N reactions leading from (Z)- 1 to (Z)- 8 and (Z)- 12 respectively, with PhCH₂SH, conjugate nucleophilic addition to 7, with Me₂NH, conjugate nucleophilic addition followed by a S_N2 to 11 , as well as several cases of nonstereoselective, probably A_N-E, reactions leading to 3,6,9 and 10. In spite of their diversified reactivity, bromoenurononitriles like 1 , partial synthetic equivalent of 2 , constitute useful synthetic intermediates.     

Recherches dans la série des cyclitols,XL. Préparation de cyclopentane-triols et de cyclopentène-triols et -diols

Two as yet unknown cyclopentene-triols have been prepared. The replacement of the halogen of cyclopentene derivatives brominated in the allylic position has been investigated. In the presence of dimethyl sulfoxide and sodium hydrogen carbonate, the bromine of some of the above mentioned allylic derivatives or the tosyloxy group of a dibenzoyloxy-monotosyloxy-cyclopentane derivative is replaced by a hydroxyl group without formation of any keto compound. The mechanism of action of the substitution agents is discussed.     

Etude structurale et magnétique de pérovskites de formule Ba3Fe2−xHoxUO9

The compounds crystallize in cubic perovskite-type system. The space group is Fm3m and the cell is entirely ordered. 4a positions (Wyckoff's notation) contain iron and uranium, 4b positions, barium and iron, 8c positions, barium and any holmium, which therefore fills coordinance-12 crystallographic sites. For iron-rich compounds (0 < x ? 0.8), interactions between Fe³⁺ ions from two magnetic sublattices 4a and 4b are antiferromagnetic. The interactions between the third magnetic sublattice, which corresponds to Ho³⁺ ions filling 8c positions, and the resultant of the first two, are slightly ferromagnetic. Such data have been obtained with all the other compounds for which the formula is Ba₃Fe_2?xLn_xUO₉, where Ln is Yb, Tm, Er, Dy, Tb, and Gd.     

Environnement tetraedrique de l'ion Cu et structure fine du seuil d'absorption K dans quelques chromites: application à l'étude d'oxydes à valence mixte

Copper zinc and copper manganese spinel chromites are studied using neutron diffraction. Cr³⁺ ions in tetrahedral environments are observed in CuCr₂O₄ and Cu_0.25Zn_0.75Cr₂O₄. These results leads to a new interpretation of the optical spectra (drs). The measurement of X-ray absorption fine structure of copper in the near edge rayon (Xanes) have been obtained using the Lure synchrotron radiation sources (Orsay, France). The spectra of Cu²⁺ in the tetrahedral environment of a quadratic or cubic matrix are characterized by the splitting of the main peak in the range 18–23 eV above the 1s → 3d transition. The X-ray absorption spectroscopy reveals the two oxidation states of copper in mixed oxides such as CuCrMnO₄. The copper(I) 1s → 4s transition is observed as a shoulder located at 10 eV on the slope of the main peak. A finer structure appears in the derivative spectrum.     

Etude par spectrométrie Mössbauer des carbures de Fer Fe3C et Fe5C2

Mössbauer spectra of Fe₃C and Fe₅C₂ have been obtained from 4°K up to the Curie temperature of each carbide. The asymmetry parameter of the Fe_I atom of Fe₃C is close to 1. The splitting of site II of Fe₅C₂ is observed. A comparison of the quadrupole splittings of Fe₃C and Fe₅C₂, in the paramagnetic state, leads us to attribute sites I and II of Fe₅C₂ to Fe_I and Fe_II, respectively. In the case where there is only a spin direction for Fe_I, this direction is located in the planes or near the planes (a, c) or (a, b).     

Le vibrateur ch2, un auxiliaire approprié à l''étude structurale d''alcanes substttues par des groupements polaires : II. Polyhalogéno-propanes

The vibrational spectra of some polyhalogeno-propanes (1,3-dibromopropane. 1,2,3- trichloropropane, 1,2,3-tribromopropane, 1,2,2,3-tetrachloropropane) are investigated in the region 1400–1500 cm⁻¹. The results demonstrate that the bending mode frequency δ(CH₂) of a CH₂X group depends on the nature of the halogen X and on the direction in space of C-X' bonds located in the or position (CH₂X-CX'-). The application of these rules enables the conformation of 1,3-difluoropropane and 1,2,2,3-tetrabromopropane to be studied for the first time.     

Etude cinétique des effets de fluence énergétique,de débit de fluence,et d'effacement induits par des ions lourds et des photons γ dans le triacétate de cellulose

The kinetic interpretation of the damage produced by heavy ions (Kr and Cl from 1 MeV/amu) and γ radiation in cellulose triacetate leads to an exponential dependence on the ion fluence. A comparison of the fading effect produced by heavy ions and γ rays shows that the heavy ions, unlike γ rays, cause irreversible damage. Finally, a nonlinear dependence on the flux of ions and γ rays is found in the kinetics of radiation damage. This result is contrary to the usual assumption that heavy-ion flux, like γ-ray flux, is additive, at least for the fluxes of 10⁹?2 × 10¹⁰ ions/cm²s and dose rates of 10³–10⁴ Gy/h used in this work.     

Préparation de dithiényl-2-éthène-1,2, de dithiényl-2-pyrimidine-2,4 et de dithiényl-2-pyridazine-3,6

The condensation of 2-thienylmagnesium bromide with (Z)-1,2-dichloroethene 2,4-dichloropyrimidne, 3,6-dichloropyridazine and with a transition metal catalyst is described. The yields of these reactions are very good; 1,2-bis(2-thienyl)ethene and two new heterocyclic compounds 2,4-bis92-thientyl)pyrimidine and 3,6-bis(2-thienyl)pyridazine were obtained in one step from commercial products.     

Analyse des spectres de vibration infrarouge et Raman de benzothiazolines et de 2H-chromènes, éléments constitutifs de spiropyrannes benzothiazoliniques. Aspect synthétique

Study of infrared and Raman spectra of benzothiazolines and 2H-chromenes, constitutive parts of benzothiazolinic spiropyrans. Synthetic aspect. We have synthesized some benzothiazolines and some substituted 2 H-chromenes as models of the two halves of benzothiazolinic spiropyrans with the aim of interpretation of infrared and Raman spectra of spiropyranic structure. While doing that, we have been able to improve the synthesis method of chromenes obtained from coumarins and we have prepared new nitro-chromenes. By studying IR. and Raman spectra of the two halves of spiropyranic molecule, we could propose a rather good attribution of fondamental modes of vibration. This attribution will used as base for the interpretation of IR. and Raman spectra of a series a benzothiazolinic spiropyrans.