R. Enjalbert

The New Oxygen-Deficient Fluorite Bi3NbO7: Synthesis, Electrical Behavior and Structural Approach

A new single phase of composition Bi{sub 3}NbO{sub 7} has been isolated in the binary system Bi{sub 2}O{sub 3}-Nb{sub 2}O{sub 5}. X-ray single crystal diffraction studies have shown that Bi{sub 3}NbO{sub 7} crystallizes in the cubic system, space group Fm{bar 3}m, with unit-cell parameter a = 5.4788(9) {angstrom}. The structure has been determined, and the final reliability index is R = 0.027. Bi{sub 3}NbO{sub 7} exhibits a defect fluorite-type structure with 12.5% of anion vacancies and appears to show a disorder in both anionic and cationic lattices. The study by electron diffraction and high resolution electron microscopy has shown the presence of an incommensurate cubic lattice. Bi{sub 3}NbO{sub 7} shows good behavior as an ionic conductor up to 875 C without any phase transition as deduced from impedance measurements.

Crystal chemistry of the VA element trihalides: Lone pair, stereochemistry, and structural relationships

Abstract The crystal structures of NCl 3 , PCl 3 , PBr 3 , AsF 3 , and AsCl 3 liquids at room temperature have been recently determined. The data for the last two are reported in the present paper. The structures of the following trihalides are discussed and classified in structural types: AsF 3 , SbF 3 , αBiF 3 , YF 3 (NCl 3 , PCl 3 , PBr 3 , βSbCl 3 , βSbBr 3 , γBiF 3 , and βBiCl 3 ), AsBr 3 (AsCl 3 , AsBr 3 , “αSbCl 3 ,” and αSbBr 3 ), PI 3 and αAsI 3 (αAsI 3 , SbI 3 , and BiI 3 ). Structural relationships have been established between AsF 3 and XeO 3 , P X 3 E and PO X 3 ( X = Cl, Br), and AsBr 3 E has been compared with PuBr 3 and VOCl 3 . A structural mechanism is proposed for the polymorphic transformation αSbBr 3 /ai βSbBr 3 . The CrCl 3 structure type is proposed for the high-temperature form of AsI 3 and a mechanism is given for the phase transition αAsI 3 /ai βAsI 3 . A proposal is made for a possible high-pressure transformation of the αAsI 3 structure into a VF 3 structure type. The stereochemistry is discussed in terms of coordination polyhedra around M∗ ; all these trihalides are characterized by a basic molecular unit M∗X 3 . The steric effects of the lone pair E carried by M∗ is especially emphasized and discussed; two characteristics of E are presented: the centroid of the electronic doublet located by E c and the sphere of influence located by its center E s . The correlative variations of M∗E c and M∗E s are studied according to the nature of M∗ (N(III), P(III) to Cl(V), Ga(I) to Br(V), In(I) to Xe(VI), and Tl(I) to Po(IV)).

An answer to the spiro versus ansa dilemma in cyclophosphazenes: Part IV. Reaction of spermidine and spermine on N3P3Cl6

Abstract Reactions of N3P3Cl6 with spermidine and spermine lead to unique final products in which two new types of configuration for the polyamino ligand, called SPIROBINO and DISPIROBINO respectively, are made conspicuous by concerted use of high resolution NMR, mass spectrometry and X-ray analysis. The product obtained by reaction of spermine on N3P3Cl6 is [N3P3Cl4HN(CH2)3N(CH2)2]2. It crystallizes in the monoclinic system, space group P21/c. The cell parameters are a=10.397(2), b = 7.869(2), c = 17.898(3) A, β = 102.1(1)°, V = 1431.6(4) A3, Z = 2 (considering the dimer), Dc = 1.748 Mg m−3, 2814 unique reflections, R = 0.042. The crystal structure shows a two-ring bridged-assembly DISPIRO pattern.

Structural evolution of the Aurivillius framework in the solid solutions Bi2WO6-Sb2WO6

Abstract The existence of two solid solutions of Bi2 − xSbxWO6 composition is demonstrated, the first one isostructural with the ferroelectric Bi2WO6 oxide (SSB, 0 ≤ x ≤ 1.25), and the second one (SSS, 1.5 ≤ x ≤ 2) isostructural with the ferroelastic Sb2WO6 compound. Both structures keep the basic framework of Aurivillius oxides, but the study of the structural evolution with x in SSB phases shows the progressive distortion of Bi2WO6 prototype network, that can be related to their possible ferroelectric behavior. The Bi-O2-Bi arrangement of Bi2O2 layers for x = 0 transforms to Bi,Sb-O-O-Bi,Sb for x > 0, being the interspace region between oxygen sheets, along [001] direction, larger for larger x values. This fact is correlated to the less stereochemical activity of 6s2 lone pair of electrons of Bi3+ relative to the 5s2 electrons of Sb3+ cation. The SSB orthorhombic structure remains until such (Bi,Sb)2O2 modification cannot be assumed by the framework, leading to the SSS triclinic structure.

Crystal structure of Nd2Te4O11: An example of a rare earth tellurium oxide

Abstract The preparation and growth of single crystals and crystal structure determination of Nd2Te4O11 are reported. It crystallizes in the monoclinic system, space groupC/2c,with parametersa = 12.635(6)A,b = 5.204(1)A,c = 16.277(3)A, β = 106.02(8)°, andZ = 4.An agreement factor ofR = 2.3%was obtained after refinement of positional and anisotropic thermal parameters. The structure is described as an interconnecting network of NdO8 distorted square antiprisms, which link in two dimensions through edge sharing, with TeO4 polyhedra which link in the same two dimensions through corner sharing. Sheets of (Nd2O10)∞ join with those of (Te8O20)∞ to form a three-dimensional network. The location and role of the lone pairs are discussed. The structure can also be described as a distorted hcp array of oxygen ions, neodymium ions, and lone pairs in which tellurium ions occupy selected trigonal bipyramidal sites.

CH3CN: X-ray structural investigation of a unique single crystal. β → α phase transition and crystal structure

The phase transition from the low- (β) to the high-temperature (α) form of acetonitrile, CH3CN, has been directly observed and studied on a unique single crystal. Both the β and α structures have been determined at temperatures close to the transition temperature (206 K and 201 K), taking advantage of the hysteresis. A single crystal of the β form was obtained for the first time.

Single-crystal X-ray investigations of the structures of γ(H)Bi2MoO6 and its partially substituted As3+ and Sb3+ homologues

In order to establish the possible existence of the solid solutions Bi2−xSbxMoO6 and Bi2−yAsyMoO6, solid state syntheses were realized and single phases obtained with 0≤x<1 and 0≤y<0.5 homogeneity ranges. High quality single crystals of the γ(H)-Bi2MoO6 prototype structure were grown for the first time and carefully refined (R=0.048) by X-ray single-crystal techniques. This phase crystallizes in the monoclinic system, space group P21/c; the observed general atomic architecture confirms a previous neutron diffraction investigation on a powder sample. A detailed description of the structure is given showing the imbrication of three different module types: A: {Bi12O14}n column, B: {Bi2Mo2O10}n and C: {BiMo3O12}n ribbons. Both Bi2−xSbxMoO6 and Bi2−yAsyMoO6 phases crystallize with γ(H) structure and the fine structural analysis performed for several values of x and y indicate that Sb and As atoms are preferentially located in specific Bi sites at the periphery of the typical A and B modules. These results are discussed in the light of the typical coordination of the lone pair cations BiIII, SbIII and AsIII, the latter adopting the one-sided coordination CN3, while the two former Sb and Bi can present CN4 and CN5 coordinations.

Crystal and molecular structure of the two MACRO-ANSA and MACRO-SPIRO isomeric cyclotriphosphazenes N3P3Cl4 [HN(CH2)3O(CH2)4O(CH2)3NH]

Abstract Reaction of N 3 P 3 Cl 6 with 4,9-dioxadodecane-1,12-diamine (coded as 3O4O3) proceeds cleanly to yield two isomeric cyclotriphosphazenic species, namely MACRO-ANSA (3O4O3) and MACRO-SPIRO (3O4O3), depending on experimental conditions. These two chemicals crystallize in monoclinic and orthorhombic systems, respectively. MACRO-ANSA (3O4O3): P 2 1 / n , a =15.405(7), b =8.728(2), c =15.685(5)A, β=98.10(3)°, V =2088 A 3 , Z =4, D X =1.52(3) Mg m −3 , R =0.077 for 1743 unique observed reflections and 247 variable parameters. MACRO-SPIRO (3O4O3): P 2 1 2 1 , a =12.638(4), b =17.364(9), c =19.334(14) A, V =4242A 3 , Z =8, D X =1.50(5) Mg m −3 , R =0.046 for 1395 unique observed reflections and 441 variable parameters. The structures of these two isomers exhibit a spatial arrangement N 3 P 3 Cl 4 with [HN(CH 2 ) 3 O(CH 2 ) 4 O(CH 2 ) 3 NH] as a 17-membered arch onto two P atoms of the N 3 P 3 ring for the MACRO-ANSA derivative and as a 15-membered loop on one P atom of the N 3 P 3 ring for the MACRO-SPIRO compound.

An original oxide of antimony and tungsten related to Aurivillius phases

Aurivillius s phases exhibit original [Bi2O2]n layers; up to now such phases exist only with bismuth. The aim of this paper is to report new related phase, containing only antimony, which is promissing because its ferroelastic properties. Synthesis, crystal growth and structure determination of the original double oxide Sb2WO6 has been performed. It crystallizes in the triclinic system, space group P1, with a=5.554(1), b=4.941(2), c=9.209(3)A, α=90.05(3), β=96.98(2), γ=90.20(2)°, V=250.8(7)A3. TEM and optical microscopy investigations allow to evidence a ferroelastic behaviour at room temperature with a phase transition in the range 300–400°C. The crystal structure of Sb2WO6 is built up by [WO4]n layers of WO6 octahedra sharing corners sandwiched by two [Sb2O2]n layers; it can be described as [WO2Sb2O4]n thick layers held together by weak Sb...O interactions. The antimony atoms exhibit typical 3+1 one sided coordination. Via structural relationships with Sb2O3, VOSb2O4 and Bi2WO6, Sb2WO6 is related with the Aurivillius phases announcing how [Bi2O2]n layers with the shape encountered in red PbO can be formed or distorted.

A New Mixed Oxide with (Bi12O14)n Columns: PbBi12Mo5O34

The title compound, lead(II)dodecabismuth(III) pentamolybdenum(VI) oxide, was prepared by solid-state methods. The structure consists of (Bi12O14)8n+n columns surrounded by (MoO4)2− tetrahedra. The Pb atoms occupy specific sites between four tetrahedra.