Synthese,purification et analyses du tetrafluorure (SeF4) et de l'oxydifluorure de selenium (SeOF2) Enthalpie de fusion et enthalpie de vaporisation de SeOF2

Selenium tetrafluoride and selenium oxydifluoride have been prepared and various analyses (chemical, thermal, microsublimation, mass spectrometry) have been performed on pure samples. The temperature and heat of fusion and heat of vaporisation of SeOF₂ have been determined.

     

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.     

Préparations et propriétés du diarséniure de beryllium:BeAs2, et du diantimoniure de beryllium:BeSb2

These compounds are obtained through solid-state reaction between the elements in sealed tubes. They remain unaltered with atmospheric moisture. X-ray diffraction gives evidence for pseudocubic symmetry. The atomic stacking is considered to be of disordered sphalerite type. BeAs₂ and BeSb₂ behave as semiconductors.     

Etude cristallochimique du vanadate NaSrVO4 et de son homologue NaSrCrO4

NaSrVO₄ has three allotropic modifications. The transformations which appear at 530 and 810°C are reversible. The structural evolution corresponds to a progressive increase of the symmetry and can be explained by the theories of M. Buerger. The parallel homologous compound NaSrCrO₄ has been investigated.     

Determination des constantes de dissociation ionique du chlorure de nitrosyle et de N2O4 dans le sulfolane

Determination of the ionic dissociation constants of nitrosyl chloride and dinitrogen tetroxide in sulpholane.

A silver chloride—silver electrode is used to study electrochemical systems involving nitrosyl chloride and dinitrogen tetroxide in sulpholane: Ag↓ + NOCl AgCl↓ + NO⁺ + e^- and Ag↓ + NOCl + NO^-₃ AgCl↓ + N₂O₄ + e^- The dissociation constants of these two NO⁺ donors determined in this way are: K_(NOCl) = 10^-11.8 mol l^-1 and K_(N2O4) = 10^-7.2 mol l^-1. A titration of N₂O⁴ solutions alone or in the presence of nitric acid is described. This titration is possible in mixtures which contain up to 90% (w/w) nitric acid.     

Synthèse en monocristaux et structure du monouranate de sodium β-Na2UO4

β-Na₂UO₄ single crystals were synthesized from a melt with U, Nb, and Na ions. They are orthorhombic Fmmm with a = 5.802(2), B = 5.969(2), and c = 11.699(3) Å, and Z = 4. The structure was refined to R = 0.075 and R_w = 0.096 for 603 independent reflexions with I ≥ 3σ(I). The study shows that Na and O atoms are delocalized and that the structure results from the juxtaposition of four P2₁/b domains.     

Détermination de la structure cristalline du ferrite de baryum Ba2Fe6O11

The crystal structure of dibarium triferrite Ba₂Fe₆O₁₁ has been solved by direct methods, using intensity data collected by means of an automated diffractometer (MoKα radiation) and corrected for absorption. It crystallizes in the orthorhombic space group Pnnm: a = 23.024(10)Å, b = 5.181(3) Å, c = 8.900(4) Å, Z = 4. Program MULTAN was successfully used for locating Ba²⁺ and most of the Fe³⁺ ions. The structure was further refined by conventional Fourier and least-squares methods (full-matrix program) to a final R value of 0.045 for 1448 observed reflections. Fe³⁺ ions occur in both octahedral (FeO mean distance: 2.02 Å) and tetrahedral (FeO mean distance: 1.865 Å) coordination. Two types of Ba²⁺ ions are found, with six and seven neighboring oxygen atoms. The structure consists of sheets of edge-shared FeO₆ octahedra which are connected by means of corner-shared tetrahedra.     

Un nouveau tetraedre azote NaN4: Preparation et structure de NaGe2N3

The NaGe₂N₃ nitride is prepared from the NaGeON oxynitride. It presents a normal tetrahedral structure related to the wurtzite type. The unit cell is orthorhombic with a = 9.8662(15), b = 5.7830(9), and c = 5.1221(5) Å, space group Cmc2₁ (No. 36). The structure refinement has been made using multicomponent profile analysis of time-of-flight neutron diffraction data. The germanium and sodium atoms are ordered among one-half of the tetrahedral sites built up by the slightly distorted hexagonal close-packing of the nitrogen atoms. It is the first example of a stable entirely nitrided environment for the sodium atom.     

Etude spectroscopique du role des liaisons PF et PO pontes dans les composes oxyfluores du phosphore V. Cas de P2O3F4 et de K2P2O5F2.

The compounds P₂O₃F₄ and K₂P₂O₅F₂ have been studied by vibrational spectroscopy. From the shifts of the symmetric vibration of the terminal PO bonds it appears that the molecular structure contracts as the number of PO (bridged) and/or PF bonds increases. The changes occur at the expense of PO terminal bonds. In these tetrahedral phosphorus (V) compounds the PO (bridged) and PF bonding have a similar role, and the same phenomenon occurs in sulfur VI oxide fluoride compounds.     

Structure de La2Fe2S5 et de La2Fe1.87S5

The compound La₂Fe₂S₅ is orthorhombic. Cell parameters are: a = 3.997(2)Å; b = 16.485(5)Å; c = 11.394(4)Å. Space group is Cmc2₁ (Z = 4. In the cell, chains of polyedra comprised of sulfur atoms tetrahedrally or octahedrally coordinating centrally located iron atoms give a monodimensional character to the structure. This one is refined to R = 0.037. To complete the study of these chains, in the La₂Fe_2?xS₅ system, vacancies are introduced on iron atom sites. The ordered compound, La₂Fe_1.87S₅, having such vacancies, is an orthorhombic superstructure of the stoechiometric compound. Cell parameters are: a = 3.9996(5)Å; b = 49.508(3)Å; c = 11.308(3)Å. Space group is Cmc2₁ and Z = 12. The structure is refined to R = 0.068. Only two iron atom sites have vacancies. One is tetrahedral, the other octahedral. In this last case the chain deformations are the more important. The chain becomes a sort of tunnel made of atoms of sulfur, with in its center the short iron-iron separation of 2.82 Å.     

Détermination du champ de force de valence des composés de coordination trans PdIIL2X2(L = (CH3)2S et (CD3)2S; X = Cl,Br et I) discussion de la structure moléculaire à partir des effets isotopiques du deuterium

A valence force field of the coordination compounds trans Pd[(CH₃)₂S]₂X₂ has been computed. This calculation is based on the infrared and Raman spectra of normal and perdeuterated complexes. The effect of geometry on isotopic shifts and values of the low vibrational frequencies indicates a distortion of the ligand around the PdS bond. The force constant of the coordination bond increases by 10 % when going from benzene solution to the solid state at 80 K.     

Structure cristalline du metatitanate de thallium Tl2TiO3

A thallium titanate oxide Tl₂TiO₃ has been prepared. It is orthorhombic, space groupPnam, with unit cell dimensions a = 12.41 A?,b = 9.615 A?,c = 3.752 A?. The structure contains double chains of edge sharing TiO₅ trigonal bipyramids, in the z direction. In this compound, thallium I has a stereochemically active lone pair. There are four oxygens bonded to thallium, all to one side.     

E´tude the´orique de la conformation de la 1,1-dime´thylhydrazine et du complexe (CH3)2N-NH2 · BF3

CNDO/2 calculations are performed in order to determine the preferred conformations of 1,1-dimethylhydrazine and 1,1-dimethylhydrazine-boron trifluoride complex. In each case, the calculations reveal the existence of an equilibrium between gauche and trans forms (25 % of trans form in the free molecule, 65 % in the complex). In agreement with experiment, the results confirm that BF₃ is attached to the nitrogen atom bearing the methyl groups.     

Sur la preparation du difluorure de vanadium VF2

Two new preparation methods of vanadium (+II) fluoride are discussed:VF₂ is obtained by action of vanadium metal on VF₃ or substitution of chlorine by fluorine in VCl₂. The later method gives very pure VF₂ at relatively low temperature.     

Etude de divers types de diastereotopie par RMN de 1H et de 13C dans les series du ferrocene et du titanocene

The influence of a chiral group on the ¹H and ¹³C NMR parameters of ferrocenes and titanocenes is studied. The difference of screening due to the diastereotopy of the cyclopentadienyl carbon nuclei is usually larger than the non-equivalence of corresponding proton chemical shifts. If the chiral group is the titanium atom itself a diastereotopy is also introduced into the cyclopentadienyl ring. Proton spectra obtained at 250 MHz, INDOR and off-resonance experiments, using chemical shift reagents permit a complete analysis of the proton and carbon spectra of some derivatives, especially ferrocene with a CH(CH₃)(CH₂CO bridge and titanocene with a CH(CH₃)CH₂CH₂ bridge. The result give information on the stereochemistry, and preferred conformations are identified.     

Synthese,structure cristalline et analyse vibrationnelle de l'hexathiohypodiphosphate de lithium Li4P2S6

The crystalline compound Li₄P₂S₆ is obtained either by devitrification of Li₄P₂S₇ glass at 450°C with sulfur formation or by crystallisation at 450°C of a Li₂S, P and S melt. The structure determination has been solved by X-ray diffraction on a monocrystal. The unit cell is hexagonal $\text{P6}{}_3\text{mcm}$ with a = 6.070(4), c = 6.577(4) Å, V = 209 ų, Z = 1. Intensities were collected at 293°K with Kα (λ = 0.71069 Å) Mo radiation on an automatic Nonius CAD-4 diffractometer. The structure was solved under the assumption of random disorder of P atoms over two sites (occupancy factor of 0.5). Anisotropic least-squares refinement with W = 1 gave R = 0.047 for 90 independent reflections and 9 variables. The structure is built according to an ABAB sequence sulfur packing. Per unit cell, four out of six octahedral sites are occupied by Li ions, and the other two are statistically filled (0.5) by PP pairs. The PP central bond (2.256(13) Å) links two staggered PS₃ groups (PS = 2.032(5) Å) to form the D_3d symmetry P₂S^4?₆ anion. Infrared and Raman spectra show features very similar to those of Na₄P₂S₆, 6H₂O and M^IIPS₃ compounds. A new assignment in terms of symmetry species is proposed for the P₂S₆ internal modes, which is confirmed by a normal coordinate calculation using a valence force field; the stretching force constants f_PP and f_PS are equal to 1.6 and 2.7 mdyne Å^?1, respectively.