Mohamed Faouzi Zid

Structure cristalline de K3NbAs2O9

Abstract K3NbAs2O9 is a new compound of Mr = 503.4: orthorhombic, Pnma, a = 22.389(6), b = 5.436(1), c = 7.870(2) A, V = 957.8 A3, Z = 4, ρ = 3.495 g/cm3, Ag K α , λ = 0.5608 A, μ = 97.6 cm−1, F(000) = 1287, R = 0.050, wR = 0.046 for 661 independent reflections. The structure contains chains of AsO4 tetrahedra and NbO6 octahedra sharing corners. They are staggered and connected by NbO(5)As bridges to form «puckereda layers parallel to the bc plane. The K+ ions, located in channels communicating by the interlayer spaces, contribute mainly by holding together chains belonging to the same layer. Although the niobium atom is off-center in an “O6” octahedron and forms a short NbOaxial(1) distance and a long NbOaxial(5) distance, the hypothesis of square pyramidal coordination is rejected by showing indirectly the influence of the Nb atom on O(5) from a comparison between the AsOequatorial and the AsO(5) distances in the NbOAs bridges. The structure of β-TaH(PO4)2 (three-dimensional anion) derives from that of K3NbAs2O9 (two-dimensional) through the sharing of the homolog of O(1) between successive layers, thus locking the communication between the channels containing the H+ ions.

Synthesis, crystal structure, sintering and electrical properties of a new alluaudite-like triple molybdate K0.13Na3.87MgMo3O12

A new triple molybdate K0.13Na3.87MgMo3O12 was synthesized by solid state reaction. The crystal structure has been determined by single X-ray diffraction and the electrical conductivity measured by impedance spectroscopy. The title compound crystallizes in the monoclinic space group C2/c with a = 12.9325 (8) A, b = 13.5537 (9) A, c = 7.1627 (6) A, β = 112.212 (9)°, V = 1162.33 (14) A3 and Z = 4. The final agreement factors are R = 0.0241, wR (F2) = 0.0584, S(F2) = 1.22. The magnesium–molybdate 3D-framework belongs to the alluaudite type. The structure is formed by infinite chains composed of edge-sharing (Mg/Na)2O10 dimmers, which are linked together via bridging MoO4 tetrahedra, yielding to a three-dimensional framework enclosing two distinct types of hexagonal tunnels in which Na+ and K+ cations reside. The structural model is validated by bond valence sum (BVS) and charge distribution (CD) methods. Ball milling is used as mechanical means to reduce the particles sizes of the synthesized powder. At the optimal sintering temperature of 650 °C, a relative density of 81% was obtained. The microstructures were characterized by scanning electron microscopy. The compound undergoes a phase transformation at 528 °C accompanied by an abrupt increase of the electrical conductivity. Above this phase transition, the electrical conductivity reaches 10−2 S cm−1. Thus K0.13Na3.87Mg(MoO4)3 may be considered as a promising compound for developing new materials with high ionic conductivity.

4-Amino­pyridinium trans-diaqua­dioxalatochromate(III) monohydrate

In the non-centrosymmetric structure of the title compound, (C5H7N2)[Cr(C2O4)2(H2O)2]·H2O, the CrIII ion has a slightly distorted octahedral coordination environment defined by two chelating oxalato ligands in equatorial positions and two water molecules in axial positions. An extensive three-dimensional network of hydrogen bonds involving all the water molecules, the 4-aminopyridinium cation and some of the oxalate O atoms contributes to the stabilization of the structure. π–π interactions between adjacent pyridine rings provide additional stability of the crystal packing, with a closest distance between pyridine mean planes of 3.613 (1) Å.

Rede´termination de la structure cristalline de K3NbP2O9

Abstract K3NbP2O9, Mr = 416.2, Monoclinic, P21 c, a = 5.214(2), b = 17.695(6), c = 9.751(3)A, β = 90.48(4)°, V = 899.5A3, Z = 4, ϱ = 3.07 g/cm3, MoKα, λ = 0.7107A, μ = 30.4 cm−1, F(000) = 800, R = 0.058, Rw = 0.064 for 675 independent reflections. The structure contains chains of PO4 tetrahedra and NbO6 octahedra sharing corners. They are connected by Nb O(2) P bridges to form double chains parallel to the a axis, held together by the K+ ions. The niobium atom is off-center in an “O6” octahedron so that it lies in an “O5” square pyramid. The correct coordination is shown to be 6.

Pre´paration et structure cristalline de K2Nb2As2O11

Abstract K 2 Nb 2 As 2 O 11 crystallizes in the monoclinic system, space group P21/a , with a = 10.342(6), b = 10.446(5), c = 9.971(4) A˚, β = 96.72(4)°, M = 589.86, V = 1069.8(5) A˚ 3 , Z = 4 , ϱ = 3.67 g cm −1 . The crystal structure was refined (105 variables) from 1782 independent reflections collected on a Philips PW 1100 automatic diffractometer with AgKα radiation. The final R index and weighted R w index are 0.058 and 0.056, respectively. The structure consists of NbO 6 octahedra and AsO 4 tetrahedra sharing vertices, forming infinite chains (NbO 6 AsO 4 ) ∞ parallel to the a axis. Two chains are linked together by Nb O Nb and Nb O As bonds. These double chains are connected by vertices, forming a three-dimensional network. The potassium atoms are located in tunnels parallel to the a axis.

(Na0.38,Ca0.31)MgFe2P3O12

The structure of sodium calcium magnesium iron phosphate, (Na0,38,Ca0,31)MgFe2P3O12, consists of an [MgFe2(PO4)3]− framework, built up by chains of edge-sharing (FeO6–FeO6–MgO6) octahedra running along the [\overline 101] direction. The chains are linked together via the common corners of phosphate tetrahedra to form sheets parallel to the ab plane. Adjacent sheets are also connected through PO4 tetrahedra, thus giving rise to an open framework with two different kinds of channels where the Na+ and Ca2+ cations are located.

Crystal structure of 1-cyclohexylpiperazine-1,4-diium dichromate(VI)

Single crystals of 1-cyclohexylpiperazine-1,4-diium dichromate(VI), (C10H22N2)[Cr2O7], were obtained by slow evaporation at room temperature from an aqueous solution of potassium dichromate, hydrochloric acid and 1-cyclohexylpiperazine. (C10H22N2)[Cr2O7] is triclinic (P

Crystal structure of alluaudite-type Na4Co(MoO4)3.

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