Abderrahmen Guesmi

A new polymorph of 1H-nicotineamidium chloride salt, (C₆H₇N₂O)⁺·Cl⁻, was grown by slow evaporation at room temperature. It crystallizes in the monoclinic space group P2₁/m. The crystal structure study shows that the organic cations (C₆H₇N₂O)⁺ and chloride anions are organized into 2D-layers packed along the b-axis. The structural components interact by N–H···O, N–H···Cl and C–H···Cl hydrogen bonds building up a two-dimensional network. The protonated organic cations and the chloride anions show a π–Cl⁻ interaction enhancing stability to the crystal structure. A description of the hydrogen-bonding network and comparison with similar related compounds of nicotinamide and isonicotineamide are presented. The bulk morphology was also predicted and it was found that the simulated morphology predicted by Bravais–Friedel–Donnay–Harker (BFDH) model matches with the morphology of as grown single crystal. Moreover, to illustrate the intermolecular interactions in the new studied polymorph, we report also the analysis of the Hirshfeld surface and its fingerprint polts.

The synthesis of 4-azaniumyl-2,2,6,6-tetramethylpiperidin-1-ium diperchlorate, C₉H₂₂N₂²⁺·2ClO₄⁻, was carried out from an aqueous reaction of perchloric acid with 4-amino-2,2,6,6-tetramethylpiperidine. This compound was characterized by TGA–DSC analysis and single-crystal X-ray diffraction. The piperidine ring of the dication adopts a chair conformation and the orientation of the C—NH₃bond is equatorial. One of the two crystallographically independent perchlorate anions exhibits disorder [occupancies 0.625 (7) and 0.375 (7)]. The crystal packing is constituted by a succession of mixed layers parallel to the (-102) plane, made up of C₉H₂₂N₂²⁺dications and ClO₄⁻anions. These ions are linked by normal and bifurcated N—H...O hydrogen bonds withR₄⁴(12) graph-set motifs, generating a two-dimensional network. The intermolecular interactions in the crystal structure were quantified and analysed using Hirshfeld surface analysis.

To investigate the influence of P/As substitution on structures and electrical properties,e.g.the effect on material densities, two new solid P/As-doped solutions, Na₂CoP_1.60As_0.40O₇(disodium cobalt diphosphorus arsenic heptaoxide) and Na₂CoP_1.07As_0.93O₇(disodium cobalt phosphorus arsenic heptaoxide), with melilite-like structures have been synthesized by solid-state reactions. Their unit-cell parameters are in agreement with Vegard's law. The obtained structural models were investigated by the bond valence sum (BVS) and charge distribution (CHARDI) validation tools and, for the latter, the structures are described as being built on anion-centred polyhedra. The frameworks can be described as layered and formed by {[Co(P,As)₂O₇]²⁻}_∞slabs, with alkali cations sandwiched between the layers and with the interlayer spaces increased due to P/As substitution. The BVS model was extended to a preliminary simulation of the sodium conduction properties in the studied structural type and suggests that the most probable sodium conduction pathways are bidimensional, at the (002) planes.

The title compound, tetrasodium hepta(cobalt/aluminium) hexa(arsenate/phosphate), Na₄Co_5.40Al_1.07(As_0.883P_0.116O₄)₆, was prepared by a solid-state reaction. It is a new member of the family of isostructural compounds with the general formulaA₄M₇(XO₄)₆(A: Na, K;M: Ni, Co;X: P, As) that is most similar to Na₄Co_5.63Al_0.91(AsO₄)₆. The Co²⁺ions in the title compound are substituted by Al³⁺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 Co²⁺ions only. With regard to the P and As atoms, one site (site symmetrym) is simultaneously occupied by As and P, whereas in the second site there is only arsenic. The alkali cations are, as in the isostructural compounds, distributed over half-occupied crystallographic sites, with a positional disorder of one of them. The proposed structural model is based both on a careful investigation of the crystal data, as well as validation by means of bond-valence-sum (BVS) and charge-distribution (CHARDI) calculations. The correlation between the X-ray refinement and the validation results is discussed.

Crystallographic and thermodynamic investigations of the binary (NaNO₃+ RbNO₃) phase diagram at atmospheric pressure reveal the existence of an intermediate compound NaRb₂(NO₃)₃(sodium dirubidium trinitrate) previously predicted and now reported experimentally for the first time. According to a DSC analysis, the compound exhibits three allotropic forms. In its low-temperature allotropic form (α form, orthorhombic) there are two Rb (m.. site symmetry) and one Na (m..) independent crystallographic positions and three planar nitrate groups. The bond-valence-sum calculations for all atoms agree well with their oxidation states. The Rb cations are located in the (100) plane atx= ½ with 11 oxygen coordination. The Na ones are in the same plane atx= 0 and are coordinated to eight O atoms from six nitrate groups. The charge-distribution method has been used to evaluate the degree of distortion of the alkali polyhedra.

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 inter-sections 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 inter-esting conduction properties.

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_∞[BP₂O₈]³⁻helices running along [001] and constructed of boron (Wyckoff position 6b, twofold axis) and phosphorus tetrahedra. The [CoBP₂O₈]⁻anionic frameworks in the two materials are structurally similar and result from a connection in theabplane between the CoO₄(H₂O)₂coordination octahedra (6bposition) and the helical ribbons. Nevertheless, the two structures differ in the disorder schemes of the K,Ca and H₂O species. The alkali cations in the structure of the pure potassium compound are disordered over three independent positions, one of them located on a 6bsite. 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.

In the title compound, tris-odium 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 octa-hedra 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 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.

The title compound, namely lithium cobalt(II/III) bis(diphosphate), Li(4.03)Co(1.97)(P(2)O(7))(2), is a new mixed-valent lithium/cobalt(II/III) phosphate. Three metal sites out of seven are occupied simultaneously by Li(+) and Co(II/III) ions. This disorder was established both from an analysis of the atomic displacement ellipsoids and Li/Co-O bond distances, and by means of a charge-distribution (CHARDI) model, which provides satisfactory agreement on the computed charges (Q) for all the cations.