Ba3 (VO4)2-K2 Ba(MoO4)2 and Pb3 (VO4)2-K2 Pb(MoO4)2 systems

Phase equilibria in the Ba₃(VO₄)₂-K₂Ba(MoO₄)₂ and Pb3(VO₄)₂-K₂Pb(MoO₄)₂ systems have been investigated. In the first system, a continuous series of substitutional solid solutions with the palmierite structure is formed, and in the second one, the polymorphic transition in lead orthovanadate at 100°C restricts the extent of the palmierite-type solid solution to 10–100 mol % K₂Pb(MoO₄)₂. Original Russian Text ? V.D. Zhuravlev, Yu.A. Velikodnyi, A.S. Vinogradova-Zhabrova, A.P. Tyutyunnik, V.G. Zubkov, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 10, pp. 1746–1748.     

Crystal structures of phosphomolybdyl salts: Pb(MoO2)2(PO4)2 and Ba(MoO2)2(PO4)2

Crystal structures of Pb(MoO₂)₂(PO₄)₂ and Ba(MoO₂)₂(PO₄)₂ were determined. Both compounds contain the molybdyl group MoO₂. The monoclinic unit-cell parameters are a = 6.353(7), b = 12.289(4), c = 11.800 Å, β = 92°56(6), and Z = 4 for the lead salt and a = 6.383(8), b = 7.142(7), c = 9.953(8) Å, β = 95°46(8), and Z = 2 for the barium salt. $\text{P2}{}_1\text{c}$ is the common space group. The R values are respectively R = 0.027 and R = 0.031 for 1964 and 1714 independent reflections. The frameworks built up by a three-dimensional network of monophosphate PO₄ and molybdyl MoO₂ groups are similar, characterized mainly by corner-sharing PO₄ and MoO₆ polyhedra. Two oxygen atoms of each MoO₆ group are bonded to the molybdenum atom only as in other molybdyl salts.     

Synthesis of Cr2(MoO4)3

Studies on the kinetics and mechanism of the reaction leading to Cr₂(MoO₄)₃ have been made using X-ray diffraction and infrared spectroscopy. The apparent activation energy, E=285±22 kJ/mol has been calculated, based on the Ginstling-Brounstein diffusion controlled model.     

Crystal structure and magnetic properties of Li,Cr-containing molybdates Li3Cr(MoO4)3, LiCr(MoO4)2 and Li1.8Cr1.2(MoO4)3

Single crystals of LiCr(MoO₄)₂, Li₃Cr(MoO₄)₃ and Li_1.8Cr_1.2(MoO₄)₃ were grown by a flux method during the phase study of the Li₂MoO₄-Cr₂(MoO₄)₃ system at 1023 K. LiCr(MoO₄)₂ and Li₃Cr(MoO₄)₃ single phases were synthesized by solid-state reactions. Li₃Cr(MoO₄)₃ adopts the same structure type as Li₃In(MoO₄)₃ despite the difference in ionic radii of Cr³⁺ and In³⁺ for octahedral coordination. Li₃Cr(MoO₄)₃ is paramagnetic down to 7 K and shows a weak ferromagnetic component below this temperature. LiCr(MoO₄)₂ is isostructural with LiAl(MoO₄)₂ and orders antiferromagnetically below 20 K. The magnetic structure of LiCr(MoO₄)₂ was determined from low-temperature neutron diffraction and is based on the propagation vektor . The ordered magnetic moments were refined to 2.3(1) μ_B per Cr-ion with an easy axis close to the [1 1 1¯] direction. A magnetic moment of 4.37(3) μ_B per Cr-ion was calculated from the Curie constant for the paramagnetic region.The crystal structures of the hitherto unknown Li_1.8Cr_1.2(MoO₄)₃ and LiCr(MoO₄)₂ are compared and reveal a high degree of similarity: In both structures MoO₄-tetrahedra are isolated from each other and connected with CrO₆ and LiO₅ via corners. In both modifications there are Cr₂O₁₀ fragments of edge-sharing CrO₆-octahedra.     

Crystal Structure of Ternary Molybdate Rb5FeHf(MoO4)6 — a New Phase in the Rb2MoO4-Fe2(MoO4)3-Hf(MoO4)2 System

Physicochemical analysis (XRPA, DTA) was used to study phase equilibria in a ternary salt system Rb₂MoO₄-Fe₂(MoO₄)₃-Hf(MoO₄)₂ in the subsolidus region. Ternary molybdates with compositions 5:1:3, 5:1:2, and 1:1:1 have been found and synthesized. Crystal and thermal characteristics have been determined. Single crystals of the ternary molybdate Rb₅FeHf(MoO₄)₆ with a composition of 5:1:2 were grown. The crystal structure of the compound was solved using X-ray diffractometry (CAD-4 automatic diffractometer, MoK _α radiation, 1766 F(hkl), R = 0.0298). Hexagonal crystals with unit cell dimensions: a = b = 10.124(1) Å, c =15.135(3) Å, V = 1343.4(4) ų, Z = 2, ρ_calc = 4.008 g/cm³, space group P6₃. The mixed three-dimensional framework of the structure is formed from two sorts of MoO₄ tetrahedra and Fe and Hf octahedra linked through their common O-vertices. Rubidium atoms of three varieties occupy the large voids of the framework.Original Russian Text Copyright © 2004 by B. G. Bazarov, R. F. Klevtsova, A. D. Tsyrendorzhieva, L. A. Glinaskaya, and Zh. G. Bazarova__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 1038–1043, November–December, 2004.     

Subsolidus phase equilibrium in Cs2MoO4-Al2(MoO4)3-Zr(MoO4)2 system and crystal structure of new ternary molybdate Cs(AlZr0.5)(MoO4)3

The subsolidus area of Cs₂MoO₄-Al₂(MoO₄)₃-Zr(MoO₄)₂ system was studied by X-ray powder diffraction. Two new molybdates with component molar ratios of 1: 1: 1 (S₁) and 5:1:2 (S₂) were synthesized for the first time. The crystallographic parameters of the 5:1:2 compound were determined. Solution- melt crystallization and spontaneous nucleation yielded crystals of new 1:1:1 cesium aluminum zirconium molybdate Cs(AlZr_0.5)(MoO₄)₃. Its formula unit and crystal structure were refined by X-ray diffraction (1592 reflections, R=0.0249). Trigonal crystals: a=12.9441(2) ?, c=12.0457(4) ?, V=1747.86(7) ?³, Z = 6, space group R $ \bar 3 $ \bar 3 . The three-dimensional combined framework of this structure is formed by MoO₄ tetrahedrons linked through common vertices to (Al,Zr)O₆ octahedrons. Cesium atoms occupy large cavities of the framework. Crystallographic position M(1) is occupied by randomly distributed Al³⁺ and Zr⁴⁺ cations.     

Synthesis of Flower-like NaY(MoO4)2 and Optical Property of NaY(MoO4)2:Eu3+

Flower-like NaY(MoO₄)₂ particles were synthesized through a microwave-assisted hydrother-mal process followed by a subsequent calcination process. The products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron mi-croscopy. The possible formation mechanism of the flower-like NaY(MoO₄)₂ precursor was proposed. The NaY(MoO₄)₂:Eu³⁺ phosphors were also prepared and their luminescence properties showed the NaY(MoO₄)₂:Eu³⁺ materials with the emission peak at 612 nm had potential application as a red phosphor for white light-emitting diodes. Furthermore, the microwave-assisted hydrothermal process followed by a subsequent calcination process could be extended to prepare the other lanthanide molybdates with the flower-like morphology.     

Cr2(WO4)3和Cr2(MoO4)3的负热膨胀特性研究

用液相反应-前驱物烧结法制备了Cr₂(WO₄)₃和Cr₂(MoO₄)₃粉体。298～1 073 K的原位粉末X射线衍射数据表明Cr₂(WO₄)₃和Cr₂(MoO₄)₃的晶胞体积随温度的升高而增大, 本征线热膨胀系数分别为(1.274±0.003)×10^-6 K^-1和(1.612±0.003)×10^-6 K^-1。用热膨胀仪研究了Cr₂(WO₄)₃和Cr₂(MoO₄)₃在静态空气中298～1 073 K范围内热膨胀行为，即开始表现为正热膨胀，随后在相转变点达到最大值，最后表现为负热膨胀，其负热膨胀系数分别为(-7.033±0.014)×10^-6 K^-1和(-9.282±0.019)×10^-6 K^-1。     

Phase formation in the K2MoO4-Lu2(MoO4)-Hf(MoO4)2 system and the structural study of triple molybdate K5LuHf(MoO4)6

Interactions in the ternary system K₂MoO₄-Lu₂(MoO₄)₃-Hf(MoO₄)₂ have been studied by X-ray powder diffraction and differential thermal analysis. A new triple (potassium lutetium hafnium) molybdate with the 5: 1: 2 stoichiometry has been found. Single crystals of this molybdate have been grown. Its X-ray diffraction structure has been refined (an X8 APEX automated diffractometer, MoK _α radiation, 1960 F(hkl), R = 0.0166). The trigonal unit cell has the following parameters: a = 10.6536(1) ?, c = 37.8434(8) ?, V = 3719.75(9) ?, Z = 6, space group R c. The mixed 3D framework of the structure is built of Mo tetrahedra sharing corners with two independent (Lu,Hf)O₆ octahedra. Two sorts of potassium atoms occupy large framework voids. Original Russian Text ? E.Yu. Romanova, B.G. Bazarov, R.F. Klevtsova, L.A. Glinskaya, Yu.L. Tushinova, K.N. Fedorov, Zh.G. Bazarova, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 5, pp. 815–818.     

Etude structurale des molybdates doubles: Cs2Mg(MoO4)2, 4H2O et (NH4)2Mg(MoO4)2, 2H2O

Le sel double Cs₂Mg(MoO₄)₂, 4H₂O cristallise dans le syste`me monoclinique, groupe d'espace P2<sub>1/c</sub> avecZ = 2. La structure ae´te´re´soluea`l'aide d'une synthe`se de Patterson et de sommations de Fourier tridimensionnelles. La valeur finale du facteur de reliabilite´estR = 0.068. L'environnement octae´drique du magne´sium est assure´par quarte mole´cules d'eau et deux atomes d'oxyge`ne de groupements molybdates. Dans le cas du sel (NH₄)₂Mg(MoO₄)₂, 2H₂O qui cristallisee´galement dans le syste`me monoclinique, groupe d'espace P2<sub>1/c</sub> avec Z = 2, l'environnement du magne´sium est assure´par deux mole´cules d'eau et quatre atomes d'oxyge`ne de groupements molybdates. La structure est de type “kro¨hnkite”. La valeur finale du facteur de reliabilite´est: R = 0.061.     

High-pressure Raman study of Al2(WO4)3

A high-pressure Raman scattering study of the tungstate Al₂(WO₄)₃ is presented. This study showed the onset of two reversible phase transitions at 0.28±0.07 and 2.8±0.1 GPa. The pressure evolution of Raman bands provides strong evidences that both the transitions involve rotations/tilts of nearly rigid tungstate tetrahedra and that the structure of the stable phase in the 0.28-2.8 GPa range may be the same as the structure of the ambient pressure, low-temperature monoclinic (C_2h⁵) ferroelastic phase of Al₂(WO₄)₃.     

Pressure-induced phase transitions in Al2(WO4)3

The high pressure behavior of aluminum tungstate [Al₂(WO₄)₃] has been investigated up to ∼18 GPa with the help of Raman scattering studies. Our results confirm the recent observations of two reversible phase transitions below 3 GPa. In addition, we find that this compound undergoes two more phase transitions at ∼5.3 and ∼6 GPa before transforming irreversibly to an amorphous phase at ∼14 GPa.     

Phase formation in Cs2MoO4-MMoO4-Zr(MoO4)2 (M = Mn, Mg, Co, Zn) systems and crystal structure of new double molybdates Cs2MnZr2(MoO4)6 and Cs2MnZr(MoO4)4

Subsolidus phase relations in the Cs₂MoO₄-MMoO₄-Zr(MoO₄)₂ (M = Mn, Zn) ternary systems were determined, and two groups of new isostructural triple molybdates were synthesized: Cs₂MZr(MoO₄)₄ and Cs₂MZr₂(MoO₄)₆ (M = Mn, Mg, Co, Zn). Cs₂MnZr₂(MoO₄)₆ and Cs₂MnZr(MoO₄)₄ crystals were grown by spontaneous flux crystallization and used in structure solution for both groups of compounds. The Cs₂MnZr₂(MoO₄)₆ structure (a =13.4322(2) ?, c = 12.2016(3) ?, group R3, Z = 3, R = 0.0367) is a new structure type characterized by a mixed three-dimensional framework built of corner-sharing MoO₄ tetrahedra and (M, Zr)O₆ octahedra where large channels are occupied by cesium cations. Cs₂MnZr₂(MoO₄)₄ (a =5.3890(1) ?, c = 8.0685(3) ?, space group P $ \bar 3 $ \bar 3 m1, Z = 0.5, R = 0.0247) has the layered glaserite-like KAl(MoO₄)₂ type structure, where Al³⁺ octahedral positions are randomly occupied by a 0.5M²⁺ + 0.5Zr⁴⁺ mixture.     

Combinatorial topology of uranyl molybdate sheets: syntheses and crystal structures of (C6H14N2)3[(UO2)5(MoO4)8](H2O)4 and (C2H10N2)[(UO2)(MoO4)2]

Two new mixed organic-inorganic uranyl molybdates, (C₆H₁₄N₂)₃[(UO₂)₅(MoO₄)₈](H₂O)₄ (1) and (C₂H₁₀N₂)[(UO₂)(MoO₄)₂] (2), have been obtained by hydrothermal methods. The structure of 1 [triclinic, , Z=1, a=11.8557(9), b=11.8702(9), c=12.6746(9) Å, α=96.734(2)°, β=91.107(2)°, γ=110.193(2)°, V=1659.1(2) Å] has been solved by direct methods and refined on the basis of F² for all unique reflections to R1=0.058, which was calculated for the 5642 unique observed reflections (|F_o|?4σ_F). The structure contains topologically novel sheets of uranyl square bipyramids, uranyl pentagonal bipyramids, and MoO₄ tetrahedra, with composition [(UO₂)₅(MoO₄)₈]⁶⁻, that are parallel to (−101). H₂O groups and 1,4-diazabicyclo [2.2.2]-octane (DABCO) molecules are located in the interlayer, where they provide linkage of the sheets. The structure of 2 [triclinic, , Z=2, a=8.4004(4), b=11.2600(5), c=13.1239(6) Å, α=86.112(1)°, β=86.434(1)°, γ=76.544(1)°, V=1203.14(10) Å] has been solved by direct methods and refined on the basis of F² for all unique reflections to R1=0.043, which was calculated for 5491 unique observed reflections (|F_o|?4σ_F). The structure contains topologically novel sheets of uranyl pentagonal bipyramids and MoO₄ tetrahedra, with composition [(UO₂)(MoO₄)₂]²⁻, that are parallel to (110). Ethylenediamine molecules are located in the interlayer, where they provide linkage of the sheets. All known topologies of uranyl molybdate sheets of corner-sharing U and Mo polyhedra can be described by their nodal representations (representations as graphs in which U and Mo polyhedra are given as black and white vertices, respectively). Each topology can be derived from a simple black-and-white graph of six-connected black vertices and three-connected white vertices by deleting some of its segments and white vertices.     

Syntheses, structures, and properties of Ag4(Mo2O5)(SeO4)2(SeO3) and Ag2(MoO3)3SeO3

Ag₄(Mo₂O₅)(SeO₄)₂(SeO₃) has been synthesized by reacting AgNO₃, MoO₃, and selenic acid under mild hydrothermal conditions. The structure of this compound consists of cis-MoO₂²⁺ molybdenyl units that are bridged to neighboring molybdenyl moieties by selenate anions and by a bridging oxo anion. These dimeric units are joined by selenite anions to yield zigzag one-dimensional chains that extended down the c-axis. Individual chains are polar with the C₂ distortion of the Mo(VI) octahedra aligning on one side of each chain. However, the overall structure is centrosymmetric because neighboring chains have opposite alignment of the C₂ distortion. Upon heating Ag₄(Mo₂O₅)(SeO₄)₂(SeO₃) looses SeO₂ in two distinct steps to yield Ag₂MoO₄. Crystallographic data: (193 K; MoKα, λ=0.71073 Å): orthorhombic, space group Pbcm, a=5.6557(3), b=15.8904(7), c=15.7938(7) Å, V=1419.41(12), Z=4, R(F)=2.72% for 121 parameters with 1829 reflections with I>2σ(I). Ag₂(MoO₃)₃SeO₃ was synthesized by reacting AgNO₃ with MoO₃, SeO₂, and HF under hydrothermal conditions. The structure of Ag₂(MoO₃)₃SeO₃ consists of three crystallographically unique Mo(VI) centers that are in 2+2+2 coordination environments with two long, two intermediate, and two short bonds. These MoO₆ units are connected to form a molybdenyl ribbon that extends along the c-axis. These ribbons are further connected together through tridentate selenite anions to form two-dimensional layers in the [bc] plane. Crystallographic data: (193 K; MoKα, λ=0.71073 Å): monoclinic, space group P2₁/n, a=7.7034(5), b=11.1485(8), c=12.7500(9) Å, β=105.018(1) V=1002.7(2), Z=4, R(F)=3.45% for 164 parameters with 2454 reflections with I>2σ(I). Ag₂(MoO₃)₃SeO₃ decomposes to Ag₂Mo₃O₁₀ on heating above 550 °C.     

Crystal structure of binary molybdate Pr2Hf3(MoO4)9

Crystals of binary praseodymium and hafnium molybdate of Pr₂Hf₃(MoO₄)₉ composition are grown by solution-melt crystallization under spontaneous nucleation conditions. By the X-ray diffraction data (X8 Apex automated diffractometer, MoK _α radiation, 2262 F(hkl), R = 0.0170) its composition and crystal structure are determined. Parameters of the trigonal unit cell are: a = b = 9.8001(1) ? c = 58.7095(8) ?, V = 4883.15(10) ?³, Z = 6, space group R c. The crystal structure is composed of three types of polyhedra: MoO₄ tetrahedra, HfO₆ octahedra, and nine-vertex PrO₉. All three types of polyhedra are bonded among themselves by common oxygen vertices of bridging MoO₄ tetrahedra forming an openwork three-dimensional structure. Original Russian Text Copyright ? 2009 by B. G. Bazarov, V. G. Grossman, R. F. Klevtsova, A. G. Anshits, T. A. Vereshchagina, L. A. Glinskaya, Yu. L. Tushinova, K. N. Fedorov, and Zh. G. Bazarova __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 3, pp. 587–590, May–June, 2009.     

Isomerization and secondary metathesis of 2-butenes over a MoO3/Al2O3 catalyst

Transformation of cis- and trans-2-butene at 40°C was investigated over a MoO₃/A₂O₃ catalyst reduced with hydrogen and subjected to different pretreatments. Isomerization is accelerated by hydrogen preadsorbed either at low or high temperatures. The cometathesis of 2-butenes with the 1-butene intermediate, however, is enhanced only by hydrogen preadsorbed at low and suppressed by hydrogen adsorbed at high temperatures.

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- -2- 40°C MoO₃/Al₂O₃, . , , . 2- 1- , ; , .

     

Syntheses and single-crystal structures of CsTh(MoO4)2Cl and Na4Th(WO4)4

Colorless crystals of CsTh(MoO₄)₂Cl and Na₄Th(WO₄)₄ have been synthesized at 993 K by the solid-state reactions of ThO₂, MoO₃, CsCl, and ThCl₄ with Na₂WO₄. Both compounds have been characterized by the single-crystal X-ray diffraction. The structure of CsTh(MoO₄)₂Cl is orthorhombic, consisting of two adjacent [Th(MoO₄)₂] layers separated by an ionic CsCl sublattice. It can be considered as an insertion compound of Th(MoO₄)₂ and reformulated as Th(MoO₄)₂·CsCl. The Th atom coordinates to seven monodentate MoO₄ tetrahedra and one Cl atom in a highly distorted square antiprism. Na₄Th(WO₄)₄ adopts a scheelite superlattice structure. The three-dimensional framework of Na₄Th(WO₄)₄ is constructed from corner-sharing ThO₈ square antiprisms and WO₄ tetrahedra. The space within the channels is filled by six-coordinate Na ions. Crystal data: CsTh(MoO₄)₂Cl, monoclinic, P2₁/c, Z=4, a=10.170(1) Å, b=10.030(1) Å, c=9.649(1) Å, β=95.671(2)°, V=979.5(2) Å³, R(F)=2.65% for I>2σ(I); Na₄Th(WO₄)₄, tetragonal, I4₁/a, Z=4, a=11.437(1) Å, c=11.833(2) Å, V=1547.7(4) Å³, R(F)=3.02% for I>2σ(I).     

Neutron powder diffraction experiments on the layered triangular-lattice antiferromagnets RbFe(MoO4)2 and CsFe(SO4)2

Powder specimens of the layered triangular-lattice antiferromagnets RbFe(MoO₄)₂ and CsFe(SO₄)₂ were prepared and neutron powder diffraction experiments were carried out in order to determine the magnetic structure. The magnetic structure of both compounds is the so-called 120^° structure in the triangular plane and is incommensurate between the planes. The ordered moments are confined in the basal ab-plane. It is also found that RbFe(MoO₄)₂ exhibits structural phase transition at around 190 K from to .     

Catalysts for metathesis of olefins, prepared by anchoring of MoO2(acac)2 to Al2O3

New highly active catalysts for metathesis of olefins were obtained through the interaction of bis(acetylacetonato)dioxymolybdenum(VI) with surface OH groups of -Al₂O₃ and subsequent reduction in H₂ or CO.

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()(VI) OH -Al₂O₃ H₂ CO .