Etude de la decomposition thermique des polyheteroarylenes

An investigation was made of the thermal and thermooxidative decompositions of polybenzimidazopyrrolones and polybenzimidazobenzoquinolines, as well as a number of heterocyclic compounds modelling the linkages and individual fragments of these polymers. It was established that in the pyrolyses of the polyheteroarylenes and the corresponding model compounds the destruction of cycles occurs either simultaneously with cleveage of the C_ar-H bond or at a higher temperature. It was shown that the completely aromatic compounds and the heterocyclic compounds condensed with the benzene nucleus are the most thermostable of the investigated compounds. A comparative study revealed a correlation between the structures and thermal stabilities of the studied compounds.

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Zusammenfassung Die thermische und thermooxydative Zersetzung von Polybenzimidazopyrrolonen und Polybenzimidazobenzochinolinen und einige der die Bindungen und individuellen Fragmente modellierenden heterozyklischen Verbindungen dieser Polymere wurden untersucht. Es wurde festgestellt, daß bei der Pyrolyse von Polyheteroarylenen und der entsprechenden Modellverbindungen das Aufsprengen der Ringe entweder gleichzeitig mit der Spaltung der C_ar-H-Bindung oder bei höheren Temperaturen erfolgt. Von den untersuchten Verbindungen sind die vollständig aromatischen und die mit Benzolringen kondensierten heterozyklischen Verbindungen am thermostabilsten. Eine vergleichende Untersuchung der Struktur und Thermostabilität der untersuchten Verbindungen ergab eine Korrelation.

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Crystallographic data on bis-tetrafluoroammonium hexafluoronickelate (IV), (NF4)2NiF6

X-ray diffraction studies on both powdered and single crystal samples of (NF₄)₂NiF₆ have shown that the compound crystallises in a tetragonal form derived from the K₂ PtCl₆ structure. The space group is I 4/m and the unit cell dimensions are : a = 6.828 (5) Å, c = 9.270 (9) Å, c/a = 1.358, and Z = 2.     

Evolution des tenseurs de dilatation thermique en fonction de la temperature. II. Etude calorimetrique et cristallographique de la transition de phase ordre-desordre du thiophene chrome tricarbonyle C4H4SCr(CO)3

Benzenechromium tricarbonyl C₆H₆Cr(CO)₃ and thiophenechromium tricarbonyl C₄H₄SCr(CO)₃ are isomorphous at room temperature. We have measured, in the range 77–295°K, the variations of specific heat and of the tensor of thermal expansion for these two molecular compounds. The first one exhibits quite normal behavior; on the other hand, the second one exhibits a first order phase transition, monoclinic ? triclinic at T = 185°K, associated with an order-disorder phase transition. Structural evolution of thiophene-chromium tricarbonyl, during phase transition, has been explained from the variation of its tensor of thermal expansion.     

Etude theorique des ruptures thermique et photochimique de la cyclopropanone

The primary processes involved in cyclopropanone reactivity have been investigated using a SCF-CI abinitio method. The C₂C₃ bond rupture has been found to be thermally favoured and the resulting oxyallyl could have a significant lifetime. By contrast, upon photonic excitation, C₁C₂ cleavage easily occurs, but does lead to stable intermediate. This constitutes the first step of CO extrusion. The results are discussed using simple MO and valence-state considerations, and compared with those of related compounds.     

Etude thermodynamique de la decomposition thermique des hydrates du chlorure de magnesium

The thermodynamic study of the different compounds of the system MgCl₂, H₂O, HCl allows to draw the stability diagram of the 8 solid phases into a three-dimensional space (temperature, total pressure and ratio of HCl and H₂O partial pressures). The evolution of the composition of solid and gaseous phases during an isobaric heating is described. The conclusions of this study are in good agreement with the experimental results obtained in laboratory and with the industrial requirements set for the different steps of the dehydration of MgCl₂.     

Etude comparative des structures type K4NiF4 et pérovskite par la méthode des invariants

The study of K₂NiF₄ and perovskite structure type by the “method of invariants” leads to the relationship: $\text{(A-X)}{}_9\text{2}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{? (A-X)}{}_{12}\text{=}\text{constant}$, where (A-X)₉ and (A-X)₁₂ are the invariant values associated with cation A in coordination number 9 and 12. In the case where A = K⁺ and X = F^?, we propose the relationship:

$\text{(K}{}^{\mathrm{+}}\text{?F)}{}_{\mathrm{R}}\text{= 2.832 R}{}^{\mathrm{<mtext>1</mtext><mtext>11.4</mtext>}}$

where R is the coordination number.     

Etude de la structure K2NiF4 par la méthode des invariants,I. Cas des oxydes A2BO4

The study of the K₂NiF₄ structure by the “method of invariants” leads to the relationship

$\text{0.99615 V}\text{1}\text{3}\text{=β}{}_{\mathrm{B}}\text{+ψ}{}_{\mathrm{A}}\text{2}\text{1}\text{2}$

with V = a²c (β_B and ψ_A are invariant values associated with cations B and A) in compounds with K₂NiF₄ structures. Some values of ψ_A and examples are proposed.     

Etude cinetique d'une decomposition thermique par couplage de la calorimetrie et de l'analyse thermique a vitesse de decomposition constante

A method is described where the simultaneous measurement of a thermal flow (by means of Tian-Calvet type calorimetry) and of a gas flow (by means of constant decomposition rate thermal analysis) allows the knowledge at any time of the instantaneous enthalpy of thermal dissociation. The method is used to study the thermal decomposition of an industrial Al(OH)₃ gibbsite sample.     

Etude structurale des molybdates doubles: Cs2Mg(MoO4)2, 4H2O et (NH4)2Mg(MoO4)2, 2H2O

Le sel double Cs₂Mg(MoO₄)₂, 4H₂O cristallise dans le syste`me monoclinique, groupe d'espace P2<sub>1/c</sub> avecZ = 2. La structure ae´te´re´soluea`l'aide d'une synthe`se de Patterson et de sommations de Fourier tridimensionnelles. La valeur finale du facteur de reliabilite´estR = 0.068. L'environnement octae´drique du magne´sium est assure´par quarte mole´cules d'eau et deux atomes d'oxyge`ne de groupements molybdates. Dans le cas du sel (NH₄)₂Mg(MoO₄)₂, 2H₂O qui cristallisee´galement dans le syste`me monoclinique, groupe d'espace P2<sub>1/c</sub> avec Z = 2, l'environnement du magne´sium est assure´par deux mole´cules d'eau et quatre atomes d'oxyge`ne de groupements molybdates. La structure est de type “kro¨hnkite”. La valeur finale du facteur de reliabilite´est: R = 0.061.     

Etude vibrationnelle des composes (C4H4P)Mn(CO)3 et [C4H2(CH3)2P]Mn(CO)3 et calcul du champ de force du cycle C4H4P complexe

The Raman and infrared spectra (4000200 cm^?1) of (C₄H₄P)Mn(CO)₃ and (C₄D₄P)Mn(CO)₃, and of [C₄H₂(CH₃)₂P]Mn(CO)₃ and [C₄D₂(CH₃)₂P]Mn(CO)₃ in the liquid and solid states (10–400 K) have been investigated. A complete vibrational assignment is proposed and valence force fields of the (C₅H₅) and (C₄H₄P) cycles are compared. From these results, it is clearly shown that the (C₄H₄P) rings are more electrophilic and weaker π-electron donors than (C₅H₅) rings, this is in agreement with their chemical behavior.     

Evolution des tenseurs de dilatation thermique en fonction de la température. III. Etude expérimentale des oxydes PbO1,57, PbWO4, V2O5 et V2O3 et analyse des résultats

The evolution of thermal expansion tensor versus temperature has been measured by powder X-ray diffraction for PbO_1,57 (in the range 77–636°K), PbWO₄ (95–800°K), V₂O₅ (77–773°K) and V₂O₃ (77–600°K). Tensor anisotropy is explained considering structure and chemical bonds (V₂O₅, PbWO₄). We verified that the evolution of anisotropy (measured by aspherism index) is much different, according to whether the oxide presents a continuous phase transition (V₂O₃) or not (PbO_1,57, PbWO₄, V₂O₅).     

Etude radiocristallographique et calorimetrique des transitions de phase de Ag8GeTe6

Powder and single crystals of the Ag₈GeTe₆ phase have been prepared by direct synthesis and chemical vapor transport reaction (iodine), respectively. The low-temperature phase of this material has been investigated by differential scanning calorimetry analysis and X-ray diffraction. The phase transitions are interpreted as a result of low-temperature ordering of the Ag⁺ ions.     

Transition de phases observee par measures optiques sur des monocristaux de SrAlF5 et de Pb3(CrF6)2

Optical measurements have been performed on SrAlF₅ and Pb₃(CrF₆)₂ crystals elaborated by a Bridgman technique. The thermal dependence of the birefringence shows anomalies which correspond to ferroelectric-paraelectric transitions. The transitions are of first order, the tetragonal crystal symmetry is not modified.     

Etude du mecanisme de photolyse des complexes cis- et trans-[PtCl2(C2H4)(4-CH3C5H4N)]. Influence de la concentration et de la longueur d'onde

Photodimerization, photoisomerization and photosubstitution quantum yields are measured for cis- and trans-[PtCl₂(C₂H₄)(4-CH₃C₅H₄N)], at various concentrations and wavelengths. Dissociation of the platinumethylene bond o?curs with a quantum yield nearly unity when the cis-compléx is irradiated in the charge transfer bands 5d → π^*(C₂H₄). Dissociation is also observed, but with a lower efficiency, at longer wavelengths. A cis → trans-photoisomerization reaction, probably via a low energy dd excited state is observed at 313,366 and 405 nm, with a constant quantum yield.     

The crystallographic and magnetic characteristics of Sr2CrO4 (K2NiF4-type) and Sr10(CrO4)6F2 (apatite-type)

Solid-state reaction between SrCO₃, Cr₂O₃ and SrF₂ has produced the apatite phase Sr₁₀(CrO₄)₆F₂ and Sr₂CrO₄ which adopts the K₂NiF₄-type structure. The reaction outcome was very sensitive to the heating rate with rapid rise times favouring the formation of Sr₂CrO₄, which has been synthesised at ambient pressure for the first time. Powder X-ray diffraction and electron diffraction confirmed that Sr₂CrO₄ adopts a body centred tetragonal cell (space group I4/mmm) with lattice parameters a=3.8357(1) Å and c=12.7169(1) Å, while a combination of neutron and X-ray diffraction verified Sr₁₀(CrO₄)₆F₂ is hexagonal (space group P6₃/m) with lattice parameters a=9.9570(1) Å and c=7.4292(1) Å. X-ray photoelectron spectroscopy and magnetic measurements were used to characterise the oxidation states of chromium contained within these phases.     

Etude de la tétracoordination de l'etain dans deux orthothiostannates: Na4SnS4 et Ba2SnS4 (α)

The crystal structure of Na₄SnS₄ and Ba₂SnS₄ (α) were determined.Na₄SnS₄ crystallizes in tetragonal system, space group $\text{P}\text{4}\text{2}{}_1\text{c}$ with parameters a = 7.837 Å, c = 6.950 Å, Z = 2 and Ba₂SnS₄ (α) in the monoclinic system, space group $\text{P2}{}_1\text{c}$ with a = 8.481 Å, b = 8.526 Å, c = 12.280 Å, β = 112.97° and Z = 4.In these compounds, the crystal structure is built up from discrete orthothiostannate tetrahedra SnS₄. The structure of Ba₂SnS₄ (α) is modified K₂SO₄β type.     

Sur un nouveau compose doubleur de frequence,synthese, et structure du nitrate-bis-nitratotrifluoroantimonate de potassium K2SbF3(NO3)2·KNO3

The study of the KNO₃SbF₃ system shows a 3:1 stoichiometric complex the structure of which has been solved from single-crystal X-ray diffraction data (orthorhombic Cmc2₁, R = 0.045 for 882 planes). It is a potassium nitrate bis-nitratotrifluoroantimonate. Antimony atoms present an intermediary coordination between AX₃E and AX₅E types. Infrared and Raman spectra are discussed taking into account crystallographic results. A nonlinear optical test using a powder sample shows a signal with an intensity near that of KDP.     

Induction effects on IR-predissociation spectra of (SF6)2, (SiF4)2 and (SiH4)2

The observed difference in transition strength for (SF₆)₂, (SiF₄)₂ and (SiH₄)₂ IR-predissociation spectra is explained by induction effects (μ₀₁²/R₁₂⁶) which have to be included in the interaction Hamiltonian in addition to the dominant dipole-dipole term (μ₀₁²/R₁₂³).     

Oxydes de plomb: V. Etude de la texture des phases quadratique et orthorhombique de Pb3O4: Influence des defauts sur la transition de phase

Several samples of Pb₃O₄ have been prepared by oxidizing PbO in air at various temperatures in the range 705–815°K. A correlation is established between the nonstochiometry of the samples and their X-ray diffraction line profiles at 295°K which are characteristic of an orthorhombic distortion of the tetragonal lattice. In the high-temperature phase (T > 170°K), orthorhombic microdomains exist in the tetragonal matrix. The mean distortion increases with the nonstochiometry of the compound. Below 170°K Pb₃O₄ exhibits an orthorhombic phase with orthorhombic domains according to two orientation states, and para crystalline distortion. A model of texture is proposed and compared with the high-temperature one. The pretransitional effect which is observed between 250 and 170°K is correlated with the presence of orthorhombic microdomains in the high-temperature phase (tetragonal).