Redetermination de la structure cristalline de KSbF4 - Liaison fluor dans les fluoroantimonates III

The crystal structure at KSbF₄ has bee redetermined from a single crystal X-ray diffraction study. The co-ordination of antimony is of AX₆E with a distorted 3.3.1. arrangement. The anionic units form channels perpendicular to the ab plane. The lone pairs of Sb^III are situated within the tunnels, the potassium ions linking the polymeric anions.     

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.     

Structure cristalline de NaBaPO4

The crystal preparation of NaBaPO₄ is discussed. The space group and cell dimensions are $\text{C2}\text{m}$; a = 9.743(3), b = 5.622(1), c = 7.260(1) Å, β = 90.10(3)°, Z = 4. The main characteristic of the NaBaPO₄ structure consists in a statistical occupation of some special positions (4i) by Na or Ba atoms. The network is built up with PO₄ tetrahedra, NaO₆ octahedra, BaO₁₂ and MO₁₀ polyhedra (M = Na or Ba). The final R value is 0.058.     

Structure cristalline de NaSbF3NO3·H2O. Etude de la liaison hydrogene OHX (X = Cl,Br, NO3)

NaSbF₃NO₃·H₂O compound has been isolated in the SbF₃NaNO₃H₂O system. The crystal structure was determined by X-ray diffraction on a single crystal. The final R factor is 0.044. The structure is compared with those of NaSbF₃X·H₂O (X = Cl, Br). The hydrogen bonds OH…X (X = Cl, Br, NO₃) form the subject of a vibrational spectroscopic study.     

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.     

Structure cristalline de Cu4(PO4)2O

Cu₄(PO₄)₂O is a new copper-rich phosphate. The preparation is described. The unit cell is triclinic, $\text{P}\text{1}$, with a = 7.528 Å, b = 8.090 Å, c = 6.272 Å; α = 113.68°, β = 81.56°, γ = 105.77°. The structure was solved from 1526 independent reflections using Patterson and Fourier syntheses. The final R value is 0.041 for the 1217 strongest reflections. Copper sites form a three-dimensional framework. The structure consists of homogeneous layers of copper and oxygen atoms parallel to the (012) plane. Phosphorus atoms are inserted between copper and oxygen layers.     

Preparation et structure cristalline de I0.33NbSe4(I4Nb12Se48)

Single crystals with I_0.33NbSe₄ composition are grown, along with NbSe₂ crystals, by iodine vapor transport from NbSe₃. Single phase powder is obtained by heating the elements in corresponding proportions at 700°C. The structure has been studied by X-ray diffraction on a single crystal. The symmetry is tetragonal with the following parameters of the unit cell a = 9.489 Å, c = 19.13 Å. The space group is $\text{P4}\text{mnc}$ with Z = 12. The structure is built up with chains of rectangular [NbSe₈]-antiprisms. Iodine atoms are located between these chains.     

Structure cristalline de SrFeF5

The crystal structure of SrFeF₅ has been determined by single crystal X-ray diffraction methods.The unit cell is monoclinic (space group $\text{P2}{}_1\text{c}$) with a = 7.062 ± 0.001 Å, b = 7.289 ± 0.001 Å, c = 14.704 ± 0.001 Å, β = 95.40 ± 0.01° and Z = 8.The lattice is built up of spiral chains of octahedra parallel to the Oy axis. These chains are formed by (FeF₆)^3? octahedra sharing corners of the same edge. The strontium atoms bridge three neighbouring chains. The SrTiF₅, SrVF₅, SrCoF₅, and BaInF₅ phases are isostructural with SrFeF₅.     

Structure cristalline du vanadate mixte In0,6Li1,2VO4

A mixed vanadate In_0.6Li_1.2VO₄ has been synthesized from an equimolecular mixture of InVO₄ and Li₃VO₄. The exact chemical formula has been determined by a crystal structure refinement. Crystallographic data are: a = 5.763(1), b = 8.742(2), c = 6.385(3)Å, Z = 4, d_calc = 3.97 g cm^?3. Seven hundred twenty-six reflections have been used for structure determination and refinement, to a final value R = 0.019, after absorption and extinction corrections. InO₆ octahedra and VO₄ tetrahedra are linked together in the same three-dimensional network that exists in InVO₄. Nevertheless, a partial substitution of In³⁺ by Li⁺ and an insertion of Li⁺ in tetrahedral interstices occur. Vacancies exist, either in the octahedral and tetrahedral positions, In_0.6Li⁽⁶⁾_0.3□⁽⁶⁾_0.1Li⁽⁴⁾_0.9□⁽⁴⁾_0.1VO₄, or solely in the tetrahedral positions, In_0.6Li⁽⁶⁾_0.4Li⁽⁴⁾_0.8□⁽⁴⁾_0.2VO₄.     

Etude structurale de combinaisons sulfurees et seleniees du molybdene. II. Structure cristalline de Ni0,33Mo3Se4

The crystals of Ni_0,33Mo₃Se₄, are triclinic, space group $\text{P}\text{1}$, with two formula units in a cell: a = 6,727 (9) Å, b = 6,582 (11) Å, c = 6,751 (6) Å, α = 90.61° (10), β = 92.17° (10), γ = 90.98° (12.) The structure was solved by analogy with Mo₃Se₄ and refined by a full-matrix least squares program to R = 0,093 for 822 independent reflexions. The channels present in Mo₃Se₄ are occupied by Ni so that Ni_0,33Mo₃Se₄ is always a metallic compound.     

Structure cristalline de K2SO4(SbF3)2

The crystal structure of K₂SO₄(SbF₃)₂ was determined by X-ray diffraction on a single crystal (R = 0.035 for 2264 reflections). There are two families of antimony atoms showing two different environments: AX₅E octahedron (6 coordination) and AX₆E 3.3.1 monocapped octahedron (7 coordination). The SO^2?₄ unit weakly bonded to four antimony atoms is not very distorted. This arrangement permits the minimization of π-E interactions. Infrared and Raman spectra are discussed in terms of diffraction results.     

Structure cristalline de La3ReO8

Lanthanum rhenium oxide, La₃ReO₈, crystallizes in the monoclinic system, space group C2₁ with the unit-cell dimensions a = 17.535(11), b = 11.889(7), c = 12.816(8) Å, γ = 90°, Z = 16. Single-crystal diffraction data were collected on an automatic four-circle diffractometer. The structure, determined by Patterson and Fourier methods, has been refined by full-matrix least-squares calculations to an R value of 0.09 for 4206 independent observed reflections. The presence of two superstructures along the a and b axes has made the determination of positions of oxygen atoms very difficult. It can be visualized as isolated ReO₆ octahedra defining tunnels, parallel to the b axis, occupied by a double chain of edge-shared La₄O tetrahedra.     

Etude structurale de combinaisons sulfurées et séleniées du molybdène. III. Structure cristalline de NiMo3S4

The crystals of NiMo₃S₄, are rhombohedral, space group $\text{R}\text{3}$, with two formula units in a cell: a = 6.462 Å, α = 94.68°.The structure was solved by the heavy atom method and refined by a full-matrix least-squares program to R = 0.077 for 1026 independent reflexions. The arrangement of Mo and S atoms in the cell is approximately the same as described before for Mo and Se atoms in Mo₃Se₄ and Ni_0.33Mo₃Se₄; the Ni atoms are situated along the channel based on x = 0, y = 0. However, in these two compounds the lattice of Se presents a covalent character when the lattice of S in NiMo₃S₄ has an essentially ionic character.     

Structure cristalline de RbSb2F7

The crystal structure of RbSb₂F₇ was determined by single crystal X-ray diffraction methods. The antimony atom coordination is of the AX₆E type, either monocapped octahedral or the distorded 2.2.2.1 arrangement. The anion (Sb₂F₇)^x-_x forms a polymeric layer parallel to the bc plane. There is an Sb-F-Sb bridge intermediate between the symmetric and asymmetric bridges of CsSb₂F₇ and KSb₂F₇ respectively.     

Chimie organométallique du niobium VIII. Etude détaillée de la réaction d'acétyléniques perfluorés avec (η5C5H5)2NbH3: Mise en evídence de la coupure de liaison C-F,de la formation de liaison Nb-F et de la reduction du niobium. Structure cristalline d'un dérivé niobiacyclopentadiène

Hexafluorobutyne (CF₃CCCF₃ = Hfb) reacts with Cp₂NbH₃ (Cp = η⁵-C₅H₅) affording five new complexes I–V, whose structures have been studied by mass,

Ir, ESR and NMR spectroscopy. The X-ray study of II shows the presence of a planar NbC₄ ring Nb—C(1): 2.25(5); C(1)—C(2): 1.31(7); C(2)—C(3): 1.53(8); C(3)—(4): 1.34(7); C(4)—Nb: 2.23(5) Å. With trifluoropropyne (CF₃CCH = tfp), only the analog of III, i.e. Cp₂NbFf(tfpH), has been isolated.     

Structure cristalline du composé RbEu3F10

Crystals of RbEu₃F₁₀ are cubic with a = 11.844 Å, Z = 8, and three possible space groups, $\text{Fm3m, F}\text{4}\text{3m}$, and F432. The structure has been resolved from three-dimensional X-ray data and refined by the least-squares method. The final R values are, respectively, 0.065 and 0.067 for Fm3m and $\text{F}\text{4}\text{3m}$, and are not significantly different. The rare earth symmetry is C_4v for Fm3m and C_2v for $\text{F}\text{4}\text{3m}$. Consequently, we have used the Eu³⁺ ion in the RbEu₃F₁₀ phase as a structural probe in order to state precisely the symmetry of the lanthanide site and distinguish among the possible space groups.     

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.     

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.