Abderrahmen Guesmi

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.

LiCo2As3O10: une nouvelle structure à tunnels inter­connectés

The title compound, lithium dicobalt(II) triarsenate, LiCo2As3O10, was synthesized by a solid-state reaction. The As atoms and four out of seven O atoms lie on special positions, all with site symmetry m. The Li atoms are disordered over two independent special (site symmetry -1) and general positions with occupancies of 0.54 (7) and 0.23 (4), respectively. The structure model is supported by bond-valence-sum (BVS) and charge-distribution (CHARDI) methods. The structure can be described as a three-dimensional framework constructed from bi-octahedral Co2O10 dimers edge-connected to As3O10 groups. It delimits two sets of tunnels, running parallel to the a and b axes, the latter being the larger. The Li+ ions are located within the intersections of the tunnels. The possible motion of the alkali cations has been investigated by means of the BVS model. This simulation shows that the Li+ motion appears to be easier mainly along the b-axis direction and that this material may possess interesting conduction properties.

β-Xenophyllite-type Na4Li0.62Co5.67Al0.71(AsO4)6.

The title compound, tetrasodium lithium cobalt aluminium hexa(orthoarsenate), was synthesized by a solid state reaction route. In the crystal structure, Co2+ ions are partially substituted by Al3+ in an octahedral environment [M1 with site symmetry 2/m; occupancy ratio Co:Al = 0.286 (10):0.714 (10)]. The charge compensation is ensured by Li+ cations sharing a tetrahedral site with Co2+ ions [M2 with site symmetry 2; occupancy ratio Co:Li = 0.690 (5):0.310 (5)]. The anionic unit is formed by two octahedra and three tetrahedra linked only by corners. The CoM1M2As2O19 units associate to an open three-dimensional framework containing tunnels propagating along the a-axis direction. One Na+ cation is located in the periphery of the tunnels while the other two are situated in the centres: all Na+ cations exhibit half-occupancy. The structure of the studied material is compared with those of various related minerals reported in the literature.

KCo(H2O)2BP2O8·0.48H2O and K0.17Ca0.42Co(H2O)2BP2O8·H2O: two cobalt borophosphates with helical ribbons and disordered (K,Ca)/H2O schemes.

The two title compounds, potassium diaquacobalt(II) borodiphosphate 0.48-hydrate and potassium-calcium(0.172/0.418) diaquacobalt(II) borodiphosphate monohydrate, were synthesized hydrothermally. They are new members of the borophosphate family characterized by (∞)[BP(2)O(8)](3-) helices running along [001] and constructed of boron (Wyckoff position 6b, twofold axis) and phosphorus tetrahedra. The [CoBP(2)O(8)](-) anionic frameworks in the two materials are structurally similar and result from a connection in the ab plane between the CoO(4)(H(2)O)(2) coordination octahedra (6b position) and the helical ribbons. Nevertheless, the two structures differ in the disorder schemes of the K,Ca and H(2)O species. The alkali cations in the structure of the pure potassium compound are disordered over three independent positions, one of them located on a 6b site. Its framework is characterized by double occupation of the tunnels by water molecules located on twofold rotation axes (6b) and a fraction of alkali cations; its cell parameters, compared with those for the mixed K,Ca compound, show abnormal changes, presumably due to the disorder. For the K,Ca compound, the K and Ca cations are on twofold axes (6b) and the channels are occupied only by disordered solvent water molecules. This shows that it is possible, due to the flexibility of the helices, to replace the alkali and alkaline earth cations while retaining the crystal framework.

Na3Co2(AsO4)(As2O7): a new sodium cobalt arsenate

In the title compound, trisodium dicobalt arsenate diarsenate, Na3Co2AsO4As2O7, the two Co atoms, one of the two As and three of the seven O atoms lie on special positions, with site symmetries 2 and m for the Co, m for the As, and 2 and twice m for the O atoms. The two Na atoms are disordered over two general and special positions [occupancies 0.72 (3):0.28 (3) and 0.940 (6):0.060 (6), respectively]. The main structural feature is the association of the CoO6 octahedra in the ab plane, forming Co4O20 units, which are corner- and edge-connected via AsO4 and As2O7 arsenate groups, giving rise to a complex polyhedral connectivity with small tunnels, such as those running along the b- and c-axis directions, in which the Na+ ions reside. The structural model is validated by both bond-valence-sum and charge-distribution methods, and the distortion of the coordination polyhedra is analyzed by means of the effective coordination number.

The novel arsenate Na4Co7−xAl2/3x(AsO4)6 (x = 1.37): crystal structure, charge-distribution and bond-valence-sum investigations

The title compound, tetrasodium cobalt aluminium hexaarsenate, Na(4)Co(7-x)Al(2/3x)(AsO(4))(6) (x = 1.37), is isostructural with K(4)Ni(7)(AsO(4))(6); however, in its crystal structure, some of the Co(2+) ions are substituted by Al(3+) in a fully occupied octahedral site (site symmetry 2/m) and a partially occupied tetrahedral site (site symmetry 2). A third octahedral site is fully occupied by Co(2+) ions only. One of the two independent tetrahedral As atoms and two of its attached O atoms reside on a mirror plane, as do two of the three independent Na(+) cations, all of which are present at half-occupancy. The proposed structural model based on a careful investigation of the crystal data is supported by charge-distribution (CHARDI) analysis and bond-valence-sum (BVS) calculations. The correlation between the X-ray refinement and the validation results is discussed.

Le nitrate double NaRb2(NO3)3, composé intermédiaire du système binaire isobare NaNO3 + RbNO3: études thermiques et cristallographiques

NaRb2(NO3)3 nitrate is the only intermediate compound in the system NaNO3 + RbNO3. It has, according to a thermal study, three allotropic forms. The structure of the low-temperature form is presented.

Structure cristalline et analyses thermique et de surface Hirshfeld du diperchlorate de 4-aza­niumyl-2,2,6,6-tétraméthylpipéridin-1-ium

A new organic perchlorate (C9H22N2)[ClO4]2 was synthesized by slow evaporation at room temperature and its crystal structure was determined. This compound was characterized by TGA–DSC and Hirshfeld surface analysis.

Ethyl 3-[1-(5,5-dimethyl-2-oxo-1,3,2-dioxaphosphorin-2-yl)propan-2-ylidene]carbazate: a combined X-ray and density functional theory (DFT) study.

In the title compound, C(11)H(21)N(2)O(5)P, one of the two carbazate N atoms is involved in the C=N double bond and the H atom of the second N atom is engaged in an intramolecular hydrogen bond with an O atom from the dimethylphosphorin-2-yl group, which is in an uncommon cis position with respect to the carbamate group. The cohesion of the crystal structure is also reinforced by weak intermolecular hydrogen bonds. Density functional theory (DFT) calculations at the B3LYP/6-311++g(2d,2p) level revealed the lowest energy structure to have a Z configuration at the C=N bond, which is consistent with the configuration found in the X-ray crystal structure, as well as a less stable E counterpart which lies 2.0 kcal mol(-1) higher in potential energy. Correlations between the experimental and computational studies are discussed.

Crystal structure of methyl 1-(4-fluorobenzyl)-4-methoxy-5-oxopyrrolidine-3-carboxylate, C14H16FNO4

Abstract C14H16FNO4, monoclinic, P21/n (no. 14), a = 10.189(4) Å, b = 7.742(2) Å, c = 17.240(5) Å, β = 94.50(1)°, V = 1355.8(7) Å3, Z = 4, Rgt(F) = 0.0420, wRref(F2) = 0.1183, T = 295 K.