Inversion symmetry in the spin-Peierls compound NaV2O5

At room-temperature NaV2O5 was found to have the centrosymmetric space group Pmmn. This space group implies the presence of only one kind of V site in contrast with previous reports of the non-centrosymmetric counterpart P21mn. This indicates a non-integer valence state of vanadium. Furthermore, this symmetry has consequences for the interpretation of the transition at 34 K, which was ascribed to a spin-Peierls transition of one dimensional chains of V4+.Comment: Revtex, 3 pages, 2 postscript pictures embedded in the text. Corrected a mistake in one pictur

Evidence for differentiation in the iron-helicoidal-chain in GdFe3_{3}(BO3_{3})4_{4}

We report on a single-crystal X-ray structure study of $GdFe_{3}(BO_{3})_{4}$ at room temperature and at T=90 K. At room temperature $GdFe_{3}(BO_{3})_{4}$ crystallizes in a trigonal space group R32 (No. 155), the same as found for other members of iron-borate family $RFe_{3}(BO_{3})_{4}$. At 90 K the structure of $GdFe_{3}(BO_{3})_{4}$ has transformed to the space group $P3_{1}2_{1}$ (No. 152). The low-temperature structure determination gives new insight into the weakly first-order structural phase transition at 156 K and into the related Raman phonon anomalies. The discovery of two inequivalent iron chains in the low temperature structure provide new point of view on the low-temperature magnetic properties.Comment: Subm. to Acta Cryst.

Ferroelectric displacements in multiferroic Y(Mn,Ga)O-3

We have studied the effects of substitution of Mn3+ by Ga3+ on the crystal structure of YMnO3. Y(Mn,Ga)O-3 is a magnetoferroelectric in which the ferroelectric displacements from the YO7 polyhedra are associated with buckling and tilting of the MnO5 bipyramids. The differences in ionic radius and orbital occupation between Mn3+ and Ga3+ result in an increase of the c/a lattice parameter ratio. This dilation is not associated with the displacements of MnO5 bipyramids, but with the elongation of the YO6 antiprisms. The magnitude of the local YO6 dipoles decrease with Ga substitution

A highly efficient titanium-based olefin polymerisation catalyst with a monoanionic iminoimidazolidide pi-donor ancillary ligand

The titanium complex Cp[1,3-(2',6' Me2C6H3) (2)(CH2N)(2)C=N] Ti(CH2Ph)(2), with a monoanionic eta(1)-iminoimidazolidide ancillary ligand, is shown to be a highly efficient catalyst for olefin polymerisation when activated with the Lewis acid B(C6F5)(3)

Fabrication and superconductivity of NaxTaS2 crystals

In this paper we report the growth and superconductivity of $Na_xTaS_2$ crystals. The structural data deduced from X-ray diffraction pattern shows that the sample has the same structure as $2H-TaS_2$. A series of crystals with different superconducting transition temperatures ($T_c$) ranging from 2.5 K to 4.4 K were obtained. It is found that the $T_c$ rises with the increase of $Na$ content determined by Energy-Dispersive x-ray microanalysis(EDX) of Scanning Electron Microscope (SEM) on these crystals. Compared with the resistivity curve of un-intercalated sample $2H-TaS_2$ ($T_c$ = 0.8 K, $T_{CDW} \approx$ 70 K), no signal of charge density wave (CDW) was observed in samples $Na_{0.1}TaS_2$ and $Na_{0.05}TaS_2$. However, in some samples with lower $T_c$, the CDW appears again at about 65 K. Comparison between the anisotropic resistivity indicates that the anisotropy becomes smaller in samples with more $Na$ intercalation (albeit a weak semiconducting behavior along c-axis) and thus higher $T_c$. It is thus concluded that there is a competition between the superconductivity and the CDW. With the increase of sodium content, the rise of $T_c$ in $Na_xTaS_2$ is caused mainly by the suppression to the CDW in $2H-TaS_2$, and the conventional rigid band model for layered dichalcogenide may be inadequate to explain the changes induced by the slight intercalation of sodium in $2H-TaS_2$.Comment: 8 pages, 13 figures, To appear in Physical Review

N-formyl-N '-(2-oxidobenzylidene) hydrazine-kappa(3) O, N, O '] diphenyltin(IV)

The title compound, [Sn(C6H5)(2)(C8H6N2O2)], features a five-coordinate C2NO2 coordination geometry for Sn that is intermediate between trigonal-bipyramidal and square-pyramidal