Affinement de la structure de TiNb2O7 et répartition des cations

TiNb₂O₇ is monoclinic $\text{C2}\text{m}$ with a = 20.351(3), b = 3.801(2), c = 11.882(2) Å, β = 120.19°, Z = 6. The structure, determined by Wadsley in 1961 from visual estimation of intensities, has been refined to R = 0.065 for 915 reflexions with I ≥ 3σI. This study shows that Ti and Nb are not randomly distributed: like several niobo or tantalotitanates with edge-sharing octahedra, this one shows preferential occupation of one type of site by the titanium atoms.     

Crystal growth and properties of lead pyrophosphate,Pb2P2O7

Single crystals of Pb₂P₂O₇ have been grown by the Czochralski technique. They have the triclinic space group $\text{P}\text{1}$ with cell dimensions a = 6.9627 Å, b = 6.9754Å, c = 12.764 Å, α = 96.78°, β = 91.16°, γ = 89.68°. There are four molecules per unit cell. Dielectric properties for this compound have been measured and are discussed.     

Crystal structure of Fe2P2O7

Fe₂P₂O₇ crystallizes in the $\text{C}\text{1}$ space group with lattice parameters a = 6.649(2)Å, b = 8.484(2)Å, c = 4.488(1)Å, α = 90.04°, β = 103.89(3)°, γ = 92.82(3)°, and ?_cal = 3.86 g/cc. It is essentially isostructural with β-Zn₂P₂O₇. As in the Zn compound, the bridging oxygen atom in the P₂O₇ group shows a high anisotropic thermal motion. It appears that the P-O-P bond angle is linear as a result of extensive π bonding with the p orbitals on the bridging oxygen atom. The high thermal motion is vibration of the atom into cavities in the structure.     

The 1-6 weberite Na2Te2O7 and some observations on compounds with the weberite structure

The 1-6 weberite Na₂Te₂O₇ (Imm2, a = 7.233 Å, b = 10.104 Å, c = 7.454 Å) has been prepared by high-pressure synthesis. It is shown that $\text{a}$) (the mean unit-cell dimension per formula unit) of oxide weberites A₂B₂O₇ can be represented as a linear function of the effective ionic radii of A and B. The problem of the true space-group symmetry of weberite is discussed.     

The crystal structure of a complex cerium(III) molybdate; Ce6(MoO4)8(Mo2O7)

Ce₆Mo₁₀O₃₉ crystallizes in the triclinic system with unit-cell dimensions (from single-crystal data) a = 10.148(5), Å, b = 18.764(6), Å, c = 9.566(5), Å, α = 103.12(7)°, β = 78.07(7)°, γ = 107.69(7)°, and space group $\text{P}\text{1}\text{, z = 2}$. The structure was solved using direct methods with 3113 countermeasured reflections (MoKα radiation), and refined using Fourier and least-squares techniques to a conventional R of 0.039 (ωR = 0.047). Ce₆Mo₁₀O₃₉ has a structure that consists of isolated MoO₄ tetrahedra together with one corner-shared pair of tetrahedra, linked to irregular eight-coordinate Ce(III) polyhedra. The average MoO distance of 1.77 Å, and average CeO distance of 2.52 Å are in good agreement with previously reported values.     

[2+2]-Cycloadditionen von vinylkationen

The vinylbromides $\text{1a}$ and $\text{1b}$ are allowed to react ith AgBF₄ and AgPF₆ in the presence of various olefins in CH₂Cl₂ as the solvent. Except for the reaction of cyclopentene with $\text{1a}$ all other olefins used, react with vinyl cation $\text{2}$ to form the cycloaddition products $\text{7}$, $\text{8a}$ and $\text{8b}$ in high yields.     

The pyrophosphate NaFeP2O7: A cage structure

The high-temperature form of NaFeP₂O₇ crystallizes in the monoclinic $\text{P2}{}_1\text{c}$ space group with a = 7.3244(13), b = 7.9045(7), c = 9.5745(15), Å, β = 111.858(13)°, and Z = 4. The structure has been refined from 3842 reflections leading to R = 0.040 and R_w = 0.047. The structure of II-NaFeP₂O₇ can be described by alternately stacking layers containing the FeO₆ octahedra and layers formed by the P₂O₇ groups, parallel to (001). Elongated cages are formed where two Na⁺ ions are located. The structure is compared with that of KAlP₂O₇. Both structures are built up from blocks of three polyhedra, [FeP₂O₁₁] or [AlP₂O₁₁], including a small O_octO_tetO_oct angle. These blocks are connected in such a way that several types of tunnels appear in each structure.     

A facile synthesis of 2-(6-ethoxycarbonyl-2-cis-hexenyl)-4-hydroxy-2-cyclopentenone

The title compound $\text{1b}$, a key intermediate for PGE₂ elaboration, is readily available in nine steps from furfuryl alcohol. The crucial steps include the exclusive formation of $\text{6a}$ from $\text{5}$ and the subsequent intramolecular Aldol condensation to $\text{2b}$.     

Crystal growth and X-ray data of the lead phosphates Pb4P2O9 and Pb8P2O13

Single crystals of the title compounds have been grown by the Czochralski technique. Pb₄P₂O₉ crystallizes in the space group $\text{P2}{}_1\text{c}$ with the parameters a = 9.4812 Å, b = 7.1303 Å, c = 14.390 Å, β = 104.51° and Pb₈P₂O₁₃ in $\text{C2}\text{m}$ with a = 10.641 Å, b = 10.206Å c = 14.342 Å, β = 98.34°.     

Crystal structures of V3S4 and V5S8

Crystal structures of the ordered phases of V₃S₄ and V₅S₈ were refined with single crystal data. Both are monoclinic. Chemical compositions, space groups and lattice constants are as follows: VS_1.47, $\text{I2}\text{m}$ (No. 12), a = 5.831(1), b = 3.267(1), c = 11.317(2)Å, β = 91.78(1)° and VS_1.64, $\text{F}\text{2}\text{m}$ (No. 12), a = 11.396(11), b = 6.645(7), c = 11.293(4), Å, β = 91.45(6)°. In both structures, short metal-metal bonds were found between the layers as well as within them. In comparison with the structure of Fe₇S₈, the stability of NiAs-type structure was discussed based on the detailed metal-sulfur distances.     

The crystal structure of hexathallium(I) hexatellurodigermanate(III), Tl6[Ge2Te6]

The new compound Tl₆[Ge₂Te₆] was prepared by thermal synthesis from the elements. The material is triclinic, space group $\text{P}\text{1}$, with a = 9.471(2), b = 9.714(2), c = 10.389(2) Å, α = 89.39(1), β = 97.27(1), γ = 100.79(1)°, and Z = 2. The crystal structure was determined from single-crystal intensity data measured by means of an automated four-circle diffractometer and refined to an R value of 0.053 for 1831 observed reflections. Tl₆[Ge₂Te₆] is characterized by Ge₂Te₆ units with GeGe bonds which are linked into a three-dimensional structure by Tl atoms coordinated to essentially six Te atoms. The most important mean distances are $\text{d}\text{GeGe}\text{) = 2.456}$ Å, $\text{d}\text{(}\text{GeTe}\text{) = 2.573}$ Å, and $\text{d}\text{(}\text{TlTe}\text{) = 3.515}$Å. The lone 6s electron pairs of the thallium(I) atoms exhibit significant stereochemical activity. Tl₆[Ge₂Te₆] represents a new structure type.     

3-methylthio-1,2-dithiolylium salts : Reaction with 4-hydroxy-6-methyl-2H-pyran-2-one and 4-hydroxycoumarin

The reaction of 4- and 5-aryl-3-methylthio-1,2-dithiolylium iodides with 4-hydroxy-6-methyl-2$\text{H}$-pyran-2-one and 4-hydroxycoumarin has been studied. 4-Substituted salts yielded 3-aryl-7-methyl-2-thioxo-2$\text{H}$,5$\text{H}$-pyrano [3,2-c]pyran-5-ones and 3-aryl-2-thioxo-2H,5H-pyrano[3,2-c]benzo[e]pyran-5-ones, respectively, whereas 5-substituted salts gave rise to 3-(5′-aryl-1′,2′-dithiol-3′-ylidene)-6-methyl-2$\text{H}$-pyran-2,4-diones and 3-(5′-aryl-1′,2′-dithiol-3′-ylidene)-2$\text{H}$-benzo [b]-pyran-2,4-diones.     

The crystal and molecular structure of oxo-bis[tribenzylsilicon(IV)]

Crystals of oxo-bis[tribenzylsilicon(IV)], O[(PhCH₂)₃Si]₂, are triclinic, space group P$\text{1}$, with a = 9.780(7), b = 9.938(9), c = 10.283(6) Å, α = 93.35(1), β = overall symmetry close to $\text{3}$: the SiOSi skeleton is strictly linear with SiO = 1.613(4) Å. The conformations of molecules and ions isoelectronic with O[(PhCH₂)₃Si]₂ are compared and discussed.     

Chiral synthesis of (2s,3s,7s)-3,7-dimethylpentadecan-2-yl acetate and propionate,potential sex pheromone components of the pine saw-fly neodiprion sertifer (geoff.)

A synthesis of (2S,3S,7S)-3,7-dimethylpentadecan-2-yl acetate ($\text{2}$) and propionate ($\text{3}$) is described. (2S)-2-Methyldecan-1-yl lithium ($\text{5}$) was reacted with (3S,4S)-3,4-dimethyl-γ-butyrolactone ($\text{6}$) to yield the ketoalcohol $\text{19}$ which upon Huang-Minlon reduction furnished (2S,3S,7S)-3,7-dimethylpentadecan-2-ol ($\text{1}$). Acylations gave the esters $\text{2}$ and $\text{3}$. The (2S)-2-methyldecan-1-yl lithium was obtained via asymmetric synthesis. The chiral lactone $\text{6}$ was obtained from (2S,3S)-trans-2,3-epoxybutane and dimethyl malonate.     

The structure of the fluorite-related phase Ca2Hf7O16

The atomic arrangement in the fluorite-related phase, Ca₂Hf₇O₁₆, has been determined by powder X-ray diffraction. The unit cell is rhombohedral, $\text{R}\text{3}$, with a = 9.5273Å, α = 38.801°, and Z = 1, and its volume is $\text{2}\text{1}\text{4}$ times that of the fluorite subcell from which it is derived. The cations are ordered on the cation sites of the fluorite structure with the calcium ions segregated into discrete layers parallel to the (111) fluorite plane: there is some evidence that the formal anion vacancies are also ordered.     

Idle spin behavior of the shifted hexagonal tungsten bronze type compounds FeIIFeIII2F8(H2O)2 and MnFe2F8(H2O)2

Fe^IIFe^III₂F₈(H₂O)₂ and MnFe₂F₈(H₂O)₂, grown by hydrothermal synthesis ($\text{P ? 200}\text{MPa}\text{, T = 450}\text{or}\text{380°}\text{C}$), crystallize in the monoclinic system with cell dimensions (Å): a = 7.609(5), b = 7.514(6), c = 7.453(4), β = 118.21(3)°; and a = 7.589(6), b = 7.503(8), c = 7.449(5), β = 118.06(3)°, and space group $\text{C2}\text{m}\text{, Z = 2}$. The structure is related to that of $\text{WO}{}_3\text{·}\text{1}\text{3}\text{H}{}_2\text{O}$. It is described in terms of perovskite type layers of Fe³⁺ octahedra separated by Fe²⁺ or Mn²⁺ octahedra, or in terms of shifted hexagonal bronze type layers. Both compounds present a weak ferromagnetism below T_N (157 and 156 K, respectively). Mössbauer spectroscopy points to an “idle spin” behavior for Fe^IIFe^III₂F₈(H₂O)₂: only Fe³⁺ spins order at T_N, while the Fe²⁺ spins remain paramagnetic between 157 and 35 K. Below 35 K, the hyperfine magnetic field at the Fe²⁺ nuclei is very weak: H_hf = 47 kOe at T = 4.2 K. For MnFe₂F₈(H₂O)₂, Mn²⁺ spin disorder is expected at 4.2 K. This “idle spin” behavior is due to magnetic frustration.     

Cobalt metallocycles: XIII. Preparation and x-ray crystallography of cobaltacyclopentadiene and dinuclear cobalt complexes

(η-Cyclopentadienyl)(triphenylphosphine)cobaltacyclopentadienes having an electron withdrawing substituent on the cyclopentadienyl ring, (η-C₅H₄R)(PPh₃)($\text{CoCHCHC}$H) (1b: R = COOMe; 1c: R = COMe), were prepared in reasonable yields by treatment of a solution of (η-C₅H₄R)(PPh₃)₂Co with acetylene. A non-substituted cyclopentadienyl analog (1a: R = H) was also isolated in low yield according to a similar procedure. Novel dinuclear complexes were also formed as by-products and the structure of (η-C₅H₄R)Co(PPh₂$\text{C}{}_6\text{H}{}_4\text{)(μ-C}$Me)Co(η-C₅H₄R) (2b: R = COOMe), having a μ₂,η³-benzyl moiety, was determined by an X-ray crystallographic analysis. The X-ray analyses of 1a and 1b were also carried out. Crystals of 1a are monoclinic, space group Pa, a 8.529(3), b 16.010(6), c 8.028(4) Å, β 100.31(3)°, Z = 2; crystals of 1b are monoclinic, space group P2₁/a, a 8.327(2), b 36.468(7), c 8.021(1) Å, β 98.75(2)°, Z = 4; and crystals of 2b are monoclinic, space group P2₁/c, a 10.681(2), b 30.722(7), c 8.912(1) Å, β 93.55(1)°, Z = 4. They have been refined to R = 0.034, 0.047 and 0.050, respectively.     

Crystal structures of phosphomolybdyl salts: Pb(MoO2)2(PO4)2 and Ba(MoO2)2(PO4)2

Crystal structures of Pb(MoO₂)₂(PO₄)₂ and Ba(MoO₂)₂(PO₄)₂ were determined. Both compounds contain the molybdyl group MoO₂. The monoclinic unit-cell parameters are a = 6.353(7), b = 12.289(4), c = 11.800 Å, β = 92°56(6), and Z = 4 for the lead salt and a = 6.383(8), b = 7.142(7), c = 9.953(8) Å, β = 95°46(8), and Z = 2 for the barium salt. $\text{P2}{}_1\text{c}$ is the common space group. The R values are respectively R = 0.027 and R = 0.031 for 1964 and 1714 independent reflections. The frameworks built up by a three-dimensional network of monophosphate PO₄ and molybdyl MoO₂ groups are similar, characterized mainly by corner-sharing PO₄ and MoO₆ polyhedra. Two oxygen atoms of each MoO₆ group are bonded to the molybdenum atom only as in other molybdyl salts.     

Chemistry of 4-membered cyclic nitrones (2, 3-dihydroazete 1-oxides); a novel one-step synthesis of N-acetoxy β-latams

2,3-dihydroazete 1-oxide $\text{1}$ reacts at room temperature with base, acid and lead tetraacetate to give the 5-hydroxyisoxazolidines $\text{4a}$ and $\text{4b}$, the 6H-1,2-oxazin-6-one $\text{7}$ and the N-acetoxy β-lactam $\text{8}$, respectively; the reaction with lead tetraacetate represents a simple one-step conversion of a 4-membered cyclic nitrone into a β-lactam.