Samia Yahyaoui

Crystal structure and electrical behavior of the new ceramic Ba0.7Na0.3Ti0.7Nb0.3O3

The crystal structure of the new Perovskite ceramic Ba0.7Na0.3Ti0.7Nb0.3O3 has been refined by the Rietveld method from X-ray powder diffraction data. The title compound crystallizes at room temperature in the cubic space group Pm¯ 3m with a = 3.9849(1) Aa ndZ = 1. The Rietveld refinement converged to the final crystal structure and profile indicators Rwp = 21.0, RB = 5.3. A ferro-paraelectric phase transition was detected by differential scanning calorimetry and dielectric measurements showing a relaxor behavior in this material.  2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Preparation, crystal structure, and physical characterization of a new hybrid material (C5H9N3)ZnCl4·H2O

An organic–inorganic hybrid compound (C5H9N3)ZnCl4 · H2O was synthesized by slow evaporation and characterized by single-crystal X-ray diffraction, differential scanning calorimetry, thermogravimetry, temperature-dependent X-ray powder diffraction, infrared spectroscopy, and some preliminary theoretical calculations of non-linear optic activity. The compound crystallizes in the non-centrosymmetric space group Pca21 with unit cell parameters: a = 22.714(5), b = 7.313(5), c = 7.301(5) Å, Z = 4, and V = 1212.8(12) Å3. The structure was solved using direct methods and refined by least-squares analysis [R 1 = 0.0484 and wR 2 = 0.1255]. It is built from isolated [ZnCl4]2− anions, 2,5-diaminopyridinediium [C5H9N3]2+ cations, and water molecules which are connected by a 3-D hydrogen-bond network. Thermodiffractometry and thermogravimetric analyses indicate that its decomposition proceeds through four stages leading to a new crystalline anhydrous phases.

Crystal structures of two enantiomorphous 2-ethylpiperazinediium hexaaquacopper sulfates [(R or S)-C5H14N2][Cu(H2O)6](SO4)2

Two new non-centrosymmetric copper sulfates are synthesized under slow evaporation conditions through the use of enantiomorphically pure sources of either (R)-2-methylpiperazine or (S)-2-methylpiperazine. Both crystallize in the non-centrosymmetric P21 space group, crystal data for [(R)-C5H14N2][Cu(H2O)6](SO4)2 (I), a = 6.5276(2) Å, b = 11.1955(3) Å, c = 12.4559(4) Å, β = 101.196(2)°, Z = 2, V = 892.95(5) Å3 and [(S)-C5H14N2][Cu(H2O)6](SO4)2 (II), a = 6.5188(2) Å, b = 11.1786(2) Å, c = 12.4365(3) Å, β = 101.205(1)°, Z = 2, V = 888.99(4) Å3. The three-dimensional structure networks for these compounds consist of isolated [Cu(H2O)6]2+ and [(R)-C5H14N2]2+ or [(S)-C5H14N2]2+ cations and SO 42− anions linked only by hydrogen bonds. The Cu atom is in a slightly distorted octahedral coordination environment. The crystal packings are influenced by cation-to-anion N-H…O and OW-H…O hydrogen bonds leading to an open framework structures.

1-Methyl­piperazine-1,4-diium tetra­chloridozincate hemihydrate

The crystal structure of the title compound, (C5H14N2)[ZnCl4]·0.5H2O, is built up from discrete 1-methylpiperazinediium cations with chair conformation, tetrahedral tetrachloridozincate anions and uncoordinated solvent water molecules linked together by three types of intermolecular hydrogen bonds, viz. N—H⋯Cl, N—H⋯O and O—H⋯Cl.

Thermal behavior and X-ray study of the new double salt hydrate SrCd2Cl6 · 8H2O

The double salt hydrate SrCd2Cl6 · 8H2O undergoes a phase transition at T = 318 K (phase I – (T = 318) →phase II). The structural characteristics, Raman scattering and dielectric measurements have been investigated. Phase II exhibits monoclinic symmetry (a = 17.102(6), b = 21.716(9), c = 8.582(5) Å and β = 91.58(13)°).

The structural transformation of monoclinic [(R)-C5H14N2][Cu(SO4)2(H2O)4]·2H2O into orthorhombic [(R)-C5H14N2]2[Cu(H2O)6](SO4)3: crystal structures and thermal behavior

Single crystals of [(R)-C5H14N2][Cu(SO4)2(H2O)4]·2H2O (1) were grown through the slow evaporation of a solution containing H2SO4, (R)-C5H12N2 and CuSO4·5H2O. These crystals spontaneously transform to [(R)-C5H14N2]2[Cu(H2O)6](SO4)3 (2) over the course of four days at room temperature. The same single crystal on the same mounting was used for the determination of the structure of (1) and the unit cell determination of (2). A second single crystal of the transformed batch has served for the structural determination of (2). Compound 1 crystallizes in the noncentrosymmetric space group P21 (No. 4) and consists of trimeric [Cu(SO4)2(H2O)4]2− anions, [(R)-C5H14N2]2+ cations and occluded water molecules. Compound 2 crystallizes in P21212 (No. 18) and contains [Cu(H2O)6]2+ cations, [SO4]2− anions and occluded water molecules. The thermal decompositions of compounds 1 and 2 were studied by thermogravimetric analyses and temperature-dependent X-ray diffraction.