A deuterium NMR study of D(UO2XO4), 4D2O; X = P,As

Deuterium NMR spectra have been obtained by the solid echo technique for polycrystalline samples of DUO₂XO₄, 4D₂O, with X = P (DUP) and As (DUAs). Transitions (II → I) were found, by DSC measurements, to occur at 260 and 290 K for DUP and DUAs, respectively. In the high temperature tetragonal phase I, the NMR lineshapes are consistent with motionally averaged axially symmetric electric field gradient tensors, with values for $\text{〈}\text{e}{}^2\text{qQ}\text{h}\text{〉}{}_{\mathrm{<mtext>av</mtext>}}$ of 39.2 ± 0.2 and 38.2 ± 0.2 kHz for DUP and DUAs, respectively. This requires fast chemical exchange of the deuterium atoms between all of the hydrogen-bond sites in a water layer, and participation of all of the deuterium atoms in the diffusion process. There are no discernible discontinuities in the spectra at the transition temperature suggesting that there is little change in the local structure of the water layers at the transition. The spectra disappeared at about 10 K below T_c and for DUP a distorted broader spectrum became discernible below about 200 K.     

Layered Intergrowth Phases Bi4MO8X (X=Cl, M=Ta and X=Br, M=Ta or Nb): Structural and Electrophysical Characterization

The high-temperature structural behavior of the layered intergrowth phase Bi₄TaO₈Cl, belonging to the Sillén-Aurivillius family, has been studied by powder neutron diffraction. This material is ferroelectric, space group P2₁cn, at T_C<640 K. An order-disorder transition to centrosymmetric space group Pmcn is found around 640 K, which involves disordering of TaO₆ octahedral tilts. A second phase transition, of a first-order nature, to space group P4/mmm occurs at a temperature of ∼1038 K. The crystal structures of the bromide analogs Bi₄MO₈Br (M=Nb, Ta) have also been determined at room temperature; both are isomorphous with Bi₄TaO₈Cl and exhibit maxima in dielectric constant at temperatures of approximately 588 and 450 K, respectively.     

Polymorphism in PbBiOXO4 compounds (X=V, P, As): Part II—PbBiOPO4 and PbBiOAsO4 structures and characterization of related solid solutions

Reinvestigation of PbBiOXO₄ (X=V, P, As) thermal behaviour revealed a phase transition for V- and P-compounds, but no transition for the As-compound. As shown by single-crystal X-ray diffraction and high-resolution neutron powder diffraction, α-PbBiOVO₄ transforms to β-PbBiOVO₄ at 550 °C. The two PbBiOPO₄ varieties are isomorph to the vanadate forms, while PbBiOAsO₄ adopts the β-type structure whatever the temperature. PbBiP_1−xOAs_xO₄ and PbBiV_1−xOM_xO₄ (M=As, P, Cr, Mn) solid solutions display both triclinic and monoclinic domains, and the α→β transition temperature is a function of the substitution rate. The ionic conductivity of these compounds was investigated by impedance spectroscopy. The analysis of free space in the β-PbBiOVO₄ structure allows to propose a one-dimensional oxygen diffusion pathway along [010] when the temperature increases.     

The stereochemistry of Tutton's salts X2[M(H2O)6](YO4)2

Neutron structure determinations have been made of Tutton's salts, X₂[M(H₂O)₆] (YO₄)₂, where Y = Se, X = K⁺, M = Cu²⁺; Y = S, X = K⁺, M = Ni²⁺, Cu²⁺, Zn²⁺; X = Rb⁺, Cs⁺, M = Cu²⁺. This work has shown that there are extensive hydrogen networks with almost linear hydrogen bonds from [M(H₂O)₆]²⁺ to (YO₄)^2?. The (H … O) distance increases in the Cu²⁺ series for X = K⁺ to Cs⁺ but there is no difference for the potassium copper salts when Y = Se or S. Three different distorted [M(H₂O)₆]²⁺ octahedra were found in the series (orthorhombic, tetragonal with two long and four short, or four long and two short bonds). The interatomic distances from X⁺ to the neighboring O in a distorted XO₈⁺ dodecahedron increases with increased cation size, implying that the X⁺ polyhedron is maintaining its shape.     

Synthesis and characterization of organic-inorganic hybrid compounds with a pillared layer structure: Ga2(4,4′-bpy)(XO4)2 (X=P, As)

Two organic-inorganic hybrid compounds, Ga₂(4,4′-bpy)(PO₄)₂, 1, and Ga₂(4,4′-bpy)(AsO₄)₂, 2, have been synthesized under hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction. The two compounds are isostructural and crystallize in the triclinic space group (No. 2) with a=4.9723(9) Å, b=5.770(1) Å, c=11.812(2) Å, α=78.268(3)°, β=89.159(3)° γ=88.344(3)°, V=331.7(2) Å³, Z=1, and R1=0.0377 for 1, and a=5.1111(7) Å, b=5.9327(8) Å, c=11.788(2) Å, α=79.497(2)°, β=88.870(2)°, γ=88.784(2)°, V=351.3(2) Å³, and R1=0.0264 for 2. The structure consists of neutral sheets of GaXO₄ (X=P or As) which are pillared through 4,4′-bipyridine ligands. Each oxide layer, which is formed only by four-membered rings, is constructed from corner-sharing GaO₄N trigonal bipyramids and XO₄ tetrahedra. The title compounds are two of the few examples in which the gallium atoms are exclusively five-coordinate.     

Synthesis and Structure of New BiMn2MO6 Compounds Where M=P, As, or V

The new compounds BiMn₂PO₆, BiMn₂AsO₆, and BiMn₂ VO₆ have been prepared and shown to be structurally related to several other BiA₂MO₆ compounds. The structure of BiMn₂PO₆ was refined from neutron powder diffraction data in space group Pnma with a=12.04 Å, b=5.37 Å, c=8.13 Å, and Z=4. It contains (BiO₂)¹⁻ chains and (PO₄)³⁻ tetrahedra. The observed fivefold coordination for the Mn²⁺ cations is unusual for Mn in this oxidation state.     

Synthesis and characterization of mixed metal organic-inorganic hybrid compounds with a pillared layer structure: CuVO2(4,4′-bpy)(XO4) (X=P, As)

Two mixed metal organic-inorganic hybrid compounds, CuVO₂(4,4′-bpy)(PO₄), 1, and CuVO₂(4,4′-bpy)(AsO₄), 2, have been synthesized under hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction. The two compounds are isostructural and crystallize in the monoclinic space group C2/c (No. 15) with a=21.941(2) Å, b=8.0915(7) Å, c=15.856(1) Å, β=110.424(2)°, Z=8, and R₁=0.037 for 1, and a=21.923(2) Å, b=8.2447(9) Å, c=16.176(2) Å, β=110.967(2)°, Z=8, and R₁=0.041 for 2. The structure consists of bimetallic oxide layers covalently linked through 4,4′-bpy pillars into a 3D framework. Each oxide layer is constructed from corner-sharing VO₄ and PO₄ tetrahedra and CuN₂O₃ square pyramids. On the basis of magnetic susceptibility study of 1, bond-valence calculation and the presence of dioxovanadium unit, the Cu atom is divalent and the V atom is pentavalent.     

Synthesis, crystal structure and characterization of new 12H hexagonal perovskite-related oxides Ba6M2Na2X2O17 (M=Ru, Nb, Ta, Sb; X=V, Cr, Mn, P, As)

The new Ba₆Ru₂Na₂X₂O₁₇ (X=V, Mn) compounds have been prepared by electrosynthesis in molten NaOH and their crystal structures have been refined from single crystals X-ray diffraction, space group P6₃/mmc, Z=2, for X=V: , , R₁=4.76%, for X=Mn : , , R₁=3.48%. The crystal structure is a 12H-type perovskite with a (c′cchcc)₂ stacking sequence of [BaO₃]_c, [BaO₃]_h and [BaO₂]_c′ layers. The tridimensional edifice is formed by blocks of Ru₂O₉ dimers that share corners with NaO₆ octahedra. These blocks sandwich double sheets of X⁵⁺O₄ tetrahedra. Several isotypic Ba₆M⁵⁺₂Na₂X⁵⁺₂O₁₇ materials (X=V, Cr, Mn, P, As) and (M=Ru, Nb, Ta, Sb) have been prepared by solid state reaction and characterized by Rietveld analysis. The magnetic and electric properties have been investigated and show besides the Ru⁵⁺₂O₉ typical intradimer antiferromagnetic couplings, discrepancies of both χ and ρ versus T at 50 and 100 K for Ba₆Ru₂Na₂X₂O₁₇ (X=V, As). In this work, a review of the identified Ru-hexagonal perovskite materials is also reported in order to overview the wide variety of possibilities in the field of new compounds synthesis.     

Crystal Structures, and Electrical Conducting and Magnetic Properties in the Plate Crystals of (Ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide)2·MX4 (M=Fe, Ga, X=Br; M=Fe, X=C1) Salts

By the reaction of a new donor molecule, ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide (1) with FeBr₃, GaBr₃ or FeCl₃ in CH₃CN/CS₂ charge transfer (CT) salts of 1 with counteranions of FeBr₄⁻, GaBr₄⁻ or FeCl₄⁻ (1₂·FeBr₄, 1₂·GaBr₄ and 1₂·FeCl₄) as plate crystals were obtained. Their crystal structures are apparently similar to each other, in which 1 molecules are dimerized in the parallel direction of their molecular long axes, and the dimers are stacked with changing the direction of the molecular long axes alternately to form a one- dimensional column. The counteranions intervene between the 1-stacked columns and are aligned in a zigzag manner. The room-temperature electrical conductivities of 1₂·FeBr₄ and 1₂·GaBr₄ are fairly high (10-15 S cm⁻¹), but a small value (0.8 S cm⁻¹) is obtained for 1₂·FeCl₄. For all CT salts, temperature dependences of electrical conductivity are semiconducting in spite of very small activation energies (30-90 meV). Based on the comparison between their electrical conducting and magnetic properties, it is suggested that the d spins of FeBr₄⁻ or FeCl₄⁻ ions exert almost no influence on the π conducting electrons in the 1-stacked column.     

Synthesis, structure of [H3dien]·(MF6)·H2O (M=Cr, Fe) and Fe Mössbauer study of [H3dien]·(FeF6)·H2O

Single crystals of [H₃dien]·(FeF₆)·H₂O (I) and [H₃dien]·(CrF₆)·H₂O (II) are obtained by solvothermal synthesis under microwave heating. I is orthorhombic (Pna2₁) with a=11.530(2) Å, b=6.6446(8) Å, c=13.787(3) Å, V=1056.3(2) Å³ and Z=4. II is monoclinic (P2₁/c) with a=13.706(1) Å, b=6.7606(6) Å, c=11.3181(9) Å, β=99.38(1)°, V=1034.7(1) Å³ and Z=4. The structure determinations, performed from single crystal X-ray diffraction data, lead to the R₁/wR₂ reliability factors 0.028/0.066 for I and 0.035/0.102 for II. The structures of I and II are built up from isolated FeF₆ or CrF₆ octahedra, water molecules and triprotonated amines. In both structures, each octahedron is connected by hydrogen bonds to six organic cations and two water molecules. The iron-based compound is also characterized by ⁵⁷Fe Mössbauer spectrometry: the hyperfine structure confirms the presence of Fe³⁺ in octahedral coordination and reveals the existence of paramagnetic spin fluctuations.     

Formation of [CoCl4(H2O)2] complex in CoCl2·MgCl2·8H2O double salt: structural and energetic properties of [MCl4(H2O)2] and [M(H2O)6] (M=Mg, Co)

The crystal structure of the double salt CoCl₂·MgCl₂·8H₂O has been determined by the X-ray diffraction method. It crystallizes in the space group with a=6.0976(9), b=6.308(1), c=8.579(3) Å, α=81.99(2)°, β=88.40°, γ=84.61(1)°, Z=1, and R=0.027. The crystal consists of two kinds of well separated octahedra, [CoCl₄(H₂O)₂]²⁻ and [Mg(H₂O)₆]²⁺. The former is unique as aquachloro complexes of Co²⁺. In order to elucidate the reason prepared as such unique complexes in the double salts, formation energies for [MCl₄(H₂O)₂]²⁻ and [M(H₂O)₆]²⁺ (M=Co, Mg) have been calculated by using the density functional methods, and it has been revealed that the formation energies of the first coordination sphere for the metal ions and the Cl⁻?H₂O hydrogen bond networks around [CoCl₄(H₂O)₂]²⁻ play a decisive role in forming [CoCl₄(H₂O)₂]²⁻ with the regular octahedral geometry in the double salt.     

Precipitation synthesis of lanthanide hydroxynitrate anion exchange materials, Ln2(OH)5NO3·H2O (Ln=Y, Eu-Er)

Layered lanthanide hydroxynitrate anion exchange host lattices have been prepared via a room temperature precipitation synthesis. These materials have the composition Ln₂(OH)₅NO₃·H₂O and are formed for Y and the lanthanides from Eu to Er and as such include the first Eu containing nitrate anion exchange host lattice. The interlayer separation of these materials, approximately 8.5 Å, is lower than in the related phases Ln₂(OH)₅NO₃·1.5H₂O which have a corresponding value of 9.1 Å and is consistent with the reduction in the co-intercalated water content of these materials. These new intercalation hosts have been shown to undergo facile anion exchange reactions with a wide range of organic carboxylate and sulfonate anions. These reactions produce phases with up to three times the interlayer separation of the host lattice demonstrating the flexibility of these materials.     

M1−x[W2O2X6] with M=K, Tl, Ag, Hg, Pb; X=Cl, Br—A class of mixed valence tungsten (IV,V) compounds with layered structures, W-W bonds and high conductivity

The crystal structure of WOCl₃, determined on the basis of powder diffraction data (tetragonal, P4₂/mnm, a=10.6856(6), c=3.8537(2)), is isotypic to WOI₃ and contains one-dimensional strands of edge-sharing double-octahedral W₂O_4/2Cl₆ groups connected via common corners in trans position. A W-W bond of 2.99 Å is present within the planar W₂Cl₆ groups. A series of non-stochiometric, mixed valence W(IV,V) compounds M_1−x[W₂O₂Cl₆] can be obtained from WOCl₃ by reaction with metal halides (TlCl, KCl, PbCl₂) or by reaction of elemental Hg with WOCl₄. All were characterized by single crystal structure determinations and EDX measurements (Tl_0.981(2)[W₂O₂Cl₆]: monoclinic, C2/m, a=12.7050(4), b=3.7797(1), , β=107.656(1)°; K_0.84(2)[W₂O₂Cl₆]: monoclinic, C2/m, a=12.812(3), b=3.7779(6), , β=107.422(8)°; Pb_0.549(3)[W₂O₂Cl₆]: orthorhombic, Immm,a=3.7659(1), b=9.8975(4), ; Hg_0.554(6)[W₂O₂Cl₆]: monoclinic, C2/m, a=12.8361(8), b=3.7622(3), , β=113.645(3)°). Two representatives of this family of compounds have already been reported: Na[W₂O₂Br₆] [Y.-Q. Zhang, K. Peters, H.G. von Schnering, Z. Anorg. Allg. Chem. 624 (1998) 1415-1418] and Ag_0.74[W₂O₂Br₆] [S. Imhaïne, C. Perrin, M. Sergent, Mat. Res. Bull. 33 (1998) 927-933]. The Ag containing compound can be obtained from elemental Ag and WOBr₃. The crystal structure, originally reported in the triclinic system, was redetermined and shown to be monoclinic with space group C2/m (a=13.7338(10), b=3.7769(3), , β=112.401(3)°). The crystal structures of these compounds are in close relationship to the structure of WOCl₃ and all contain W₂O_4/2X₆ (X=Cl, Br) double strands with the mono and divalent cations coordinated by the terminal halogen atoms of the W₂X₆ groups and a short W-W bond (2.85 Å for X=Cl). A cube-shaped coordination environment is present for M=Tl, K and a trigonal-prismatic coordination for M=Ag, Hg. Hg_0.55[W₂O₂Cl₆] is a semiconductor with a non-Arrhenius behaviour, high specific conductivity of 0.05 Ω^-1 cm⁻¹ and a very small activation energy of 0.03 eV. Hg_0.55[W₂O₂Cl₆] and Ag_0.8[W₂O₂Br₆] show a temperature independent paramagnetism with a magnetic moment around 300×10^-6 cm³ mol^-1.     

Mechanochemical synthesis of rutile-type CrMO4 (M=V, Sb) and their solid solutions

Grinding a mixture of hydrous amorphous chromium oxide (Cr₂O₃·nH₂O), vanadium oxide (V₂O₅) and antimony oxide (Sb₂O₅) was conducted by using a planetary ball mill, to investigate their mechanochemical reactions to form chromium vanadium oxide (CrVO₄) and chromium antimony oxide (CrSbO₄). The synthesis reactions proceed with an increase in grinding periods of time. The ground samples consist of agglomerates with particle size of about ten nanometers. The synthesized CrVO₄ sample exhibits a rutile-type tetragonal crystal structure, which is a high pressure phase. Additionally, solid solutions, CrV_1−xSb_xO₄ (x=0∼1, Δx=0.25), have been synthesized mechanochemically from the mixtures of Cr₂O₃·nH₂O, V₂O₅ and Sb₂O₅.     

Hydroxyhydrogénosels: Le phosphate et l'arséniate non-stoechiométriques de formule idéale Na3Al(OH)(HXO4)(XO4) (X = P ou As)

An aluminum-sodium phosphate and the corresponding isotypic arsenate have been synthetized. Chemical analysis, density measurements, thermogravimetry, X-ray powder diffraction, and ir spectroscopy led to the conclusion that they are nonstoichiometric hydroxyhydrogen salts of ideal formula: Na₃Al(OH)(HXO₄)(XO₄) (X = P,As), the nonstoichiometry being a result of the presence of cation vacancies which are compensated for by protons. The monoclinic unit-cell parameters have been determined. The space group is $\text{C2}\text{m}\text{, C2}$, or Cm.Z = 4.     

Phase diagrams in the quaternary systems M1−xCuxCr2X4 with M = Cd,Mn, and X = S,Se

The phase diagrams of the spinel systems Cd_1?xCu_xCr₂S₄, Cd_1?xCu_xCr₂Se₄, and Mn_1?xCu_xCr₂S₄ have been studied on the basis of X-ray powder photographs of quenched samples and high-temperature X-ray diffraction patterns. At room temperature the mutual solid solubilities of the metallic copper and the semiconducting cadmium and manganese spinels are only small (x < 0.05 and >0.95). The interchangeability, however, increases largely with increasing temperature. Complete series of mixed crystals, as in the Zn_1?xCu_xCr₂X₄ (X = S, Se) systems, however, are not formed. The solid solutions with x > 0.07 and <0.95, x > 0.095 and <0.90, and x > 0.36 and <0.87, respectively, formed at higher temperatures cannot be quenched to room temperature without decomposition. The unit cell dimensions of the spinel solid solutions studied obviously do not obey Vegard's rule.     

Stoichiometry and physical properties of ternary molybdenum chalcogenides MxMo6X8 (X = S,Se; M = Li,Sn, Pb)

Chemical and electrochemical insertion of Li at room temperature, as well as insertion of lead and tin at moderate temperatures (500°C), into the binary phase Mo₆X₈ forms ternary molybdenum chalcogenides M_xMo₆X₈ (X = S, Se). Crystallographic parameters, superconducting properties, and magnetic susceptibility are reported. The stoichiometry x for lead and tin is shown not to exceed x = 1, while for Li, x can reach approximately 4.0. For the lead and tin sulfide series, the hexagonal lattice parameters and superconducting critical temperatures (T_c) are invariant to changes in the nominal composition of 0.8 < x < 1.2, while both an increase in T_c and a small decrease in c_h is observed for the selenides; a narrow homogeneity range exists near x = 1 below 500°C for both these sulfides and selenides, the single-phase region being somewhat larger in the selenides. In contrast, several single-phase regions and large unit cell changes are observed in Li_xMo₆X₈ (0 < x < 3.2). Magnetic susceptibility measurements of the lithiated compounds at x ～ 3.2 reveals a structural phase transition at 140 and 185 K for the sulfide and selenide, respectively; but neither superconducts down to 1.5 K. At lower lithium concentration near x ～ 1.0, the T_c of the sulfide is raised from that of Mo₆S₈ (1.8 K) to 5.2 K but the T_c of Mo₆Se₈ (6.5 K) is depressed to 3.9 K.     

Application de la spectrometrie vibrationnelle à un probleme de non-stoechiométrie par insertion dans les tunnels pentagonaux des réseaux (M6X4O26) (M = Nb,Ta; X = Si,Ge)

The ir spectra of A₃M₆Si₄O₂₆ (A = Ba, Sr; M = Nb, Ta) and K₆M₆Si₄O₂₆ oxides, whose structure contains linear Si₂O₇ groups, are discussed with particular emphasis on the peculiar behavior of the antisymmetric stretching frequency of the linear SiOSi bridge. In accord with previous data, this frequency is the highest of the spectrum (near 1200 cm^?1), but it is significantly lowered (by about 75 cm^?1) when passing from the A₃M₆Si₂₄O₂₆ to the K₆M₆Si₄O₂₆ compounds. This is readily explained by the peculiar structure of the K₆ compounds, in which three (out of the six) K⁺ cations are located near the bridge oxygen (A₂ sites), these sites remaining empty in the A₃M₆Si₄O₂₆ compounds. The resulting KO bonding weakens the SiO bond, thus leading to a lowering of the corresponding bridge frequency. The same type of explanation holds for the presence of a new band at an intermediate frequency (about 1150 cm^?1) in phases of intermediate composition K_6?2xBa_xM₆Si₄O₂₆, this new band being correlated with a partial occupancy of the A₂ sites. This has been applied to, and is a sensitive means of, detecting nonstoichiometry in the A₂ sites of other compounds with (M₆X₄O₂₆) layers (X = Si, Ge) such as Ba_6+xNb₁₄Si₄O₄₇, K₈M₁₄Si₄O₄₇, and K₁₀M₂₂X₄O₆₈ (M = Nb, Ta).