MoO4 Tetrahedra Research Articles

Charge density in MoO4 tetrahedron and PbO8 octahedron in PbMoO4

The precise electronic structure of lead molybdate (PbMoO4) has been studied using powder X-ray data. The acousto-optical, photoconductivity, luminescence, ad thermoluminescence properties in PbMoO4 in general, depend on the electron density distribution in the MoO4 tetrahedron and PbO8 octahedron. Hence, a complete analysis of the bonding interaction between Mo and O atoms in MoO4 and Pb and O atoms in PbO8 has been studied. The bonding between the atoms using the maximum entropy method (MEM) and bond length distribution using pair distribution function (PDF) has been analyzed. The valence state of oxygen atom is found to be responsible for the sensible properties in PbMoO4. The particle size of PbMoO4 is also analyzed using XRD and SEM. The band gap energy has also been calculated using UV–visible spectra. A study in terms of the local structure and electron density using versatile tools like MEM and PDF is lacking in literature. Hence this work complements these aspects.

(p‐Tol3Sn)2MoO4] – A Polymeric Triorganotin Molybdate with (10,3)a Network Structure

Abstract(p‐Tol3Sn)2MoO4 was prepared by the reaction of p‐Tol3SnCl with (NBu4)2[Mo6O19] and (NBu4)OH. The title compound crystallises trigonal with a = 2769.2(2) and c = 3576.3(3) pm, space group R3. The crystal structure consists of MoO4 tetrahedra that are linked by p‐Tol3SnO2 bipyramides to give a 3D network structure and additionally every second MoO4 tetrahedron shares a corner with a terminal p‐Tol3SnO tetrahedron. (p‐Tol3Sn)2MoO4 exhibits an uninodal (10,3)a network which is related to the structure of (NBu4)[(Ph3Sn)3MoO4]·CH3CN.

Synthesis, structural and vibrational properties of microcrystalline RbNd(MoO4)2

Rubidium neodymium dimolybdate, RbNd(MoO4)2, microcrystals have been fabricated by solid state synthesis at T=550–600°C by t=324ks. Crystal structure of RbNd(MoO4)2 has been refined by Rietveld method in space group Pbcn with cell parameters a=5.1772(1)Å, b=18.7293(4)Å, and c=8.2774(1)Å (RB=5.05%). The crystal structure of RbNd(MoO4)2 consists of layers of MoO4 tetrahedrons corner-sharing with NdO8 square antiprisms. These layers are perpendicular to b-axis of the unit cell. About 20 narrow Raman lines have been observed in Raman spectrum recorded for RbNd(MoO4)2 powder sample.

Growth and crystal structure of binary molybdate CsFe(MoO4)2

CsFe(MoO4)2 single crystals have been grown by solution-melt crystallization with a charge-to-solvent ratio of 1: 3 (with Cs2Mo3O10 used as a solvent). The crystal structure of this compound has been refined by X-ray diffraction (X8 APEX automatic diffractometer, MoKα radiation, 356 F(hkl), R = 0.0178). The trigonal unit cell has the following parameters: a = b = 5.6051(2) A, c = 8.0118(4) A, V = 217.985(15) A3, Z = 1, ρcalc = 3.875 g/cm3, and sp. gr. P\( \bar 3 \)m1. The structure is composed of alternating layers of FeO6 octahedra (with MoO4 tetrahedra attached by sharing vertices) and CsO12 icosahedra.

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) A, c = 12.2016(3) A, 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) A, c = 8.0685(3) A, space group P \( \bar 3 \) 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.

Effects of doping Y on crystal structure and catalytic activity of α-Bi2Mo3O12

The single phase Y0·2Bi1·8Mo3O12 and α-Bi2Mo3O12 catalysts have been synthesised by solid state reaction, and the Y0·2Bi1·8Mo3O12 shows better catalytic performance than α-Bi2Mo3O12 in the selective oxidation of isobutene to methacrolein. X-ray powder diffraction structural analysis, X-ray photoelectron spectroscopy and O2 temperature programmed desorption have been used to reveal the effects of doping Y on the crystal structure and catalytic activity of α-Bi2Mo3O12 induced by Y substitution for Bi. It is found that when Bi in α-Bi2Mo3O12 crystal structure is partially substituted by Y with lower electronegativity, the electronic densities of oxygen will increase, which could improve the rate determining α-H abstraction at Bi sites in the selective oxidation of isobutene to methacrolein. On the other hand, the partially regularised MoO4 tetrahedra also promote the catalytic selectivity to methacrolein due to the decrease in oxidation ability. Besides, the longer interatomic distances between Mo3 and Bi in the principal cleavage plane (010) and (010) might result in the lesser catalytic activity of Mo3 sites.

Crystal Structure of Molybdenum Tantalum Oxide, Mo2Ta2O11

AbstractThe ternary molybdenum tantalum oxide Mo2Ta2O11 was synthesized through two different experimental routes. The crystal structure was determined from X‐ray powder diffraction data. Mo2Ta2O11 crystallizes in space group R\bar{3}m (no. 166) with the lattice parameters a = 562.82(2) pm and c = 2516.2(1) pm in hexagonal setting. A so far unknown layered structure with three formula units per unit cell is observed. Corner sharing TaO6 octahedra form double layers perpendicular to [001] with MoO4 tetrahedra on each side. The tetrahedra are connected by corners to the TaO6 octahedra and are isolated from each other. The crystal structure can be described in relation to the ReO3‐type.

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(AlZr0.5)(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) A, c=12.0457(4) A, V=1747.86(7) A3, Z = 6, space group R \( \bar 3 \). 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.

X-ray diffraction and vibrational Raman spectra of the Li2−xNaxCo2(MoO4)3 (0 ⩽ x ⩽ 1.4) solid solution with a lyonsite structure

Synthesis, X-ray diffraction and Raman spectroscopy studies of Li2–xNaxCo2(MoO4)3 (0⩽x⩽2) compositions have been investigated. These alkali–cobalt molybdates crystallize in the orthorhombic system (space group Pnma (D2h)) with a lyonsite structure (Z=4). The cell parameters are determined by DICVOL04 software and confirmed by Rietveld refinements. The structure is formed by a framework of MoO4 tetrahedra and (Li/Na/Co)O6 octahedra, the tetrahedra provide links between sheets and columns formed by the octahedra. The structure shows that while octahedra share corners and edges in the sheets, they share faces columns. Alkali and cobalt are distributed statically in both the octahedral and trigonal prism sites. X-ray diffraction shows the presence of a solid solution in the range of compositions (0⩽x<1.4). These results are in agreement with Raman studies where the spectra of all the compositions are similar and show linear shifts of the frequencies as a function of the composition toward low values due to the substitutions of Li+ by Na+ with a larger radius.

Crystal structure and magnetic properties of Li,Cr-containing molybdates Li 3Cr(MoO 4) 3, LiCr(MoO 4) 2 and Li 1.8Cr 1.2(MoO 4) 3

Single crystals of LiCr(MoO 4) 2, Li 3Cr(MoO 4) 3 and Li 1.8Cr 1.2(MoO 4) 3 were grown by a flux method during the phase study of the Li 2MoO 4–Cr 2(MoO 4) 3 system at 1023 K. LiCr(MoO 4) 2 and Li 3Cr(MoO 4) 3 single phases were synthesized by solid-state reactions. Li 3Cr(MoO 4) 3 adopts the same structure type as Li 3In(MoO 4) 3 despite the difference in ionic radii of Cr 3+ and In 3+ for octahedral coordination. Li 3Cr(MoO 4) 3 is paramagnetic down to 7 K and shows a weak ferromagnetic component below this temperature. LiCr(MoO 4) 2 is isostructural with LiAl(MoO 4) 2 and orders antiferromagnetically below 20 K. The magnetic structure of LiCr(MoO 4) 2 was determined from low-temperature neutron diffraction and is based on the propagation vektor k ⇒ = ( 1 2 , 1 2 , 0 ) . 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(MoO 4) 3 and LiCr(MoO 4) 2 are compared and reveal a high degree of similarity: In both structures MoO 4-tetrahedra are isolated from each other and connected with CrO 6 and LiO 5 via corners. In both modifications there are Cr 2O 10 fragments of edge-sharing CrO 6-octahedra.

Structural Characterization and Luminescent Properties of a Red Phosphor Series: Y2−xEux(MoO4)3 (x=0.4–2.0)

A series of rare earth molybdates, Y2−xEux(MoO4)3 for x=0.4, 0.8, 1.2, 1.6 and 2.0 were prepared by solid‐state method and their crystal structures, photo luminescent characteristics were investigated. The powders are mainly studied for their red light emission efficiency under near UV excitation. The crystal structures of the powders were found to depend on annealing temperature and the yttrium concentration. Mixtures of monoclinic (C2/c) and orthorhombic (Pba2, Pbna) structures were formed in varying proportions depending on the value of x and annealing temperatures (700°–800°C). The luminescence behavior depended on the resultant composition of the crystal phase and the Eu3+ concentration. The excitation spectra showed the characteristic and broad O→Mo charge transfer (CT) band of the MoO4 tetrahedra and the sharp intra‐configurational 4f–4f transitions of Eu3+ in the host lattice. The integrated emission ratio (5D0→7F2/5D0→7F1) of Eu3+ depends on the annealing temperature and reveals that the local site symmetry of Eu3+ ions decreases with increasing concentration of Eu3+. The emission spectra obtained by exciting at 396 nm, gave highest red emission intensity for Y0.4Eu1.6(MoO4)3 annealed at 700°C/6 h among this series of samples.

First Mixed Alkaline Uranyl Molybdates: Synthesis and Crystal Structures of CsNa3[(UO2)4O4(Mo2O8)] and Cs2Na8[(UO2)8O8(Mo5O20)

AbstractTwo new mixed alkaline uranyl molybdates CsNa3[(UO2)4O4Mo2O8] (1) and Cs2Na8[(UO2)8O8(Mo5O20)] (2) have been obtained by high‐temperature solid state reactions. Their crystal structures have been solved by direct methods: Compound 1: triclinic, P$\bar{1}$, a = 6.46(1), b = 6.90(1), c = 11.381(2) Å, α = 84.3(1), β = 91.91(1), γ = 80.23(1)°, V = 488.6(2) Å3, R1 = 0.06 for 2865 unique reflections with |Fo| ≥ 4σF; Compound 2: orthorhombic, Ibam, a = 6.8460(2), b = 23.3855(7), c = 12.3373(3) Å, V = 1975.2(1) Å3, R1 = 0.049 for 2120 unique reflections with |Fo| ≥ 4σF. The structure of 1 contains complex sheets of UrO5 pentagonal bipyramids and molybdenum polyhedra. The sheets have [(UO2)2O2(MoO5)] composition. Natrium and cesium atoms are located in the interlayer space. Cesium atoms are situated between the molybdenum clusters, whereas natrium atoms are segregated between the uranyl complexes. The large Cs+ ions are localized between the Mo2O9 groups and force the molybdenum polyhedra to rotate relative to the [(UO2)2O2(MoO5)] sheets. Such rotation is impossible for U6+ polyhedra due to their rigid edge‐sharing complexes. The distance between the U6+ polyhedra vertices of neighboring layers is 3.8 Å, that allows the Na+ ion to be positioned between the uranyl groups. The crystal structure of 2 is based upon a framework consisting of [(UO2)2O2(MoO5)] sheets parallel to (010). The sheets are linked into a 3‐D framework by sharing vertices with the Mo(2)O4 tetrahedra, located between the sheets. Each MoO4 tetrahedron shares two of its corners with two MoO6 octahedra in the sheet above, and the other two with MoO6 octahedra of the sheet below. Thus four MoO6 octahedra and one MoO4 tetrahedron form chains of composition Mo5O18. The resulting framework has a system of channels occupied by the Cs+ and Na+ ions.

High-Pressure Study of Gd2(MoO4)3by Raman Scattering and Ab Initio Calculations

High-pressure induced phase transitions in a single crystal of gadolinium molybdate, Gd-2(MoO4)(3) were studied by the Raman spectroscopy and ab initio calculations. The amorphization of the sample takes place at about 6 GPa in a mixture of alcohol as a pressure transmitting medium and begins as soon as 3 GPa in argon. In both media, the amorphization is irreversible in the 0-9 GPa investigated pressure range. The joint ab initio and Raman results allowed us to conclude that rotations of MoO4 tetrahedra axe the primary structural changes involved in the first phase transition (at about 2 GPa) explaining the softening of the low frequency modes at about 50 cm(-1). In addition, a progressive distortion of tetrahedra followed by a coordination change (IV-VI) of Mo atoms is observed through the five structural transitions including amorphization. This mechanism based on the steric hindrance of polyhedra is believed to be the most relevant for explaining the amorphization of Gd-2(MoO4)(3).

Correlation between AO6 Polyhedral Distortion and Negative Thermal Expansion in Orthorhombic Y2Mo3O12 and Related Materials

The Pbcn orthorhombic phase of Y2Mo3O12 has been examined through high-resolution X-ray powder diffraction (10−450 K), heat capacity determination (2−390 K), and differential scanning calorimetry (103−673 K). No phase transition was found over this temperature range. The overall thermal expansion is negative, and the average linear thermal expansion coefficient, αl, is −9.02 × 10−6 K−1 averaged over T = 20−450 K. From a thorough analysis of the structure of Y2Mo3O12, we find that the YO6 octahedra and MoO4 tetrahedra are increasingly distorted with increasing temperature. The inherent volume distortion parameter (υ) of AO6 has been introduced to quantitatively evaluate polyhedral distortion and it is observed that this parameter is strongly correlated with the linear coefficient thermal expansion (αl) of different members of the A2M3O12 family. We attribute the negative thermal expansion to the reduction of the mean Y−Mo nonbonded distances and Y−O−Mo bond angles with increasing temperature, the joint act...

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, MoKα 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) A c = 58.7095(8) A, V = 4883.15(10) A3, Z = 6, space group R\( \bar 3 \)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.

Synthesis, Characterization, and Photocatalytic Properties of ZrMo2O8

ZrMo2O8 was synthesized via two routes, namely, the traditional solid-state method and the solution combustion method. The compounds were characterized by powder X-ray diffraction, UV−visible spectroscopy, scanning electron microscopy, and transmission electron microscopy. The crystals belong to a trigonal crystal system, space group P 1c (No. 163) with a = 10.1391(6) A, c = 11.7084(8) A, and Z = 6. The band gap of the compounds was around 2.7 eV, and DFT calculations suggest the indirect nature of the band gap. The irregular MoO4 tetrahedra create a dipole and inhibit the process of electron−hole recombination, thereby making the material photoactive. The photocatalytic activity of the compounds prepared by both routes has been investigated for the degradation of various dyes under UV irradiation, and this showed the specificity of the compounds towards the degradation of non-anthraquinonic dyes.

Phase formation in the Ag2MoO4-CuO-MoO3 system and the crystal structure of the new double molybdate Ag2Cu2(MoO4)3

Subsolidus phase relations in the Ag2MoO4-CuO-MoO3 oxide-salt ternary system were determined. T-x diagram was plotted for the Ag2MoO4-CuMoO4 quasi-binary join. Double molybdate Ag2Cu2(MoO4)3 was found to exist on this join. This compound is a superstructure derived from orthorhombic Li3Fe(MoO4)3. Its structure was solved in terms of a subcell (a = 5.0749(3), b = 11.300(2), c = 18.127(3) A, space group Pnma, Z = 4, R = 0.0678). In the true unit cell, the parameter a is tripled; suggested space group is P212121. A characteristic feature of the Ag2Cu2(MoO4)3 structure is infinite columns (extended along axis a) of face-sharing oxygen octahedra, in which disordered silver atoms are located (Ag(21), Ag(22), and Ag(23)) with various degrees of irregularity of their octahedral coordination and a strong anisotropy of thermal vibrations. Distorted CuO6 octahedra form zigzag ribbons extended in the same direction. MoO4 tetrahedra, which are arranged according to the pseudo-hexagonal law, link the aforementioned major structural elements into a three-dimensional framework. Trigonal-prismatic voids of the framework are occupied by silver atoms Ag (1). Presumably, the disorder of the silver ions in octahedral columns can be responsible for the increased ion conductivity of silver copper molybdate. A partial order of the same ions is the most likely reason for the appearance of superstructure with the tripled unit cell volume.

Potassium Self-Diffusion in Potassium Bismuth/Rare Earth Molybdate Crystals

The anisotropy of self-diffusion of K+ ions, ionic conductivity, and static permittivity in stoichiometric disordered K5Bi1-xRx(MoO4)4 (R = Nd, Gd; x = 0, 0.92, 1) single crystals is studied. A high value of the 2-D diffusion and ionic conductivity by K+ ions is detected. The fast ionic transport is parallel to the double layers formed by MoO4 tetrahedrons.

Growth, Structures, and Properties of Li2Zn2(MoO4)3 and Co-doped Li2Zn2(MoO4)3

On the basis of our previous work on the investigation of the subsolidus phase relation of the system ZnO- Li2O-MoO3, we for the first time successfully prepared single crystals of Li2Zn2(MoO4)3 (I) with dimensions up to 10 × 4 × 3 mm3 and Co-doped Li2Zn2(MoO4)3 (II) with a size of 15 × 10 × 3 mm3 by using the top-seeded solution growth method. The X-ray diffraction analysis shows that the Li+ cation and transition metal ion fill in the octahedral and trigonal prism interstice composed of surrounding MoO4 tetrahedrons. The UV−vis spectra show that by doping with Co2+, there is an obvious red shift of the absorption band at 276 nm with the steep absorption edge changing from 370 nm (I) to 430 nm (II). The band gaps of I and II calculated with CASTEP are ≪ 2.4 eV and ≪ 1.9 eV, respectively, indicating that Co2+ play roles in the change of the band gap of the host crystal. The X-ray powder analysis of the system Li2−2xZn2+x(MoO4)3 suggests the framework is stable over a range of composition for −0.1 ≤ x ≤ 0....

Effect of Water Species on the Phonon Modes in Orthorhombic Y2(MoO4)3 Revealed by Raman Spectroscopy

Negative thermal expansion material of yttrium molybdate has been synthesized by rapid solidification with a CO2 laser. It crystallized in the orthorhombic phase with unique microstructures consisting of nanoparticles or nanodendrites with grain sizes around 20−30 nm. Raman spectroscopic and XRD analyses reveal that the presence of water species hinders not only the rocking motion but every type of motion of the corner shared polyhedra. Because of the presence of water species, degeneracy of the Raman bands happens for symmetric stretching, asymmetric stretching, and the bending modes, and the lattice, translational, and librational modes cannot be observed. The release of water species below 403 K (388 K for the newly prepared sample or 383 K in the second temperature cycle) has little whereas that above this temperature has great effect on the stretching and bending vibrations and also the librational and translational modes. This indicates that the water species which are released within the first step do not interact with the MoO4 tetrahedra in the Y2Mo3O12 framework while those released in the second step have a direct interaction. It is suggested that the translational and librational motions are closely coupled with stretching and bending vibrations. They together give rise to the negative thermal expansion.