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Study of phase formation in the system K2MoO4–Na2MoO4 at 500 °C showed the existence of the only double molybdate K2-xNaxMoO4 (0.4 ≤ x ≤ 1) of the glaserite-related type. Using these data, the subsolidus phase relations in the systems K2MoO4–Na2MoO4–MMoO4 (M = Mn, Zn) were studied at 470–560 °C and the extended solid solutions based on the alluaudite-type Na4−2xM1+x(MoO4)3 were found. In the structure of K1.71Na1.71Mn1.29(MoO4)3 (sp. gr. C2/c, Z = 4, a = 13.0595(3) A, b = 13.7892(3) A, c = 7.2973(2) A, β = 111.339(1)°, R = 0.0134), the potassium ions partially replace Na+ in the channels running along c-axis. The structure of K1.84Na2.11Zn1.02(MoO4)3 (sp. gr. P1, Z = 2, a = 7.3258(8) A, b = 9.4128(10) A, c = 9.4302(10) A, α = 93.104(3)°, β = 104.573(3)°, γ = 104.432(3)°, R = 0.0220) is isotypic with alluaudite-related α-K4Zn(WO4)3 and seems to be a result of stabilizing an unknown triclinic modification of K4Zn(MoO4)3 by substitution of sodium for potassium with the strong differentiation of alkali and zinc cations in the structure. In the structure of K1.5Na0.5Mn2(MoO4)3 (sp. gr. Pcca, Z = 8, a = 10.6160(7) A, b = 12.2714(8) A, c = 18.0275(11) A, R = 0.0155) of the α-K2Mn2(MoO4)3 type, one of three initial potassium positions is jointly occupied by (Na, Mn); a similar phenomenon occurs in isostructural Rb3Na3Sc2(MoO4)6. The structure contains zigzag-like ribbons of edge-sharing MnO6 octahedra linked with separate MnO6 octahedra and МоО4 tetrahedra into 3D containing channels along the c-axes filled by K+ ions. BVS maps show possible one-dimensional sodium-ion conductivity for the structures of K1.71Na1.71Mn1.29(MoO4)3 and Rb3Na3Sc2(MoO4)6.

A novel organic-inorganic hybrid supramolecular Complex (C2H8N)4SiMo12O40 based on Keggin building blocks has been successfully synthesized by solvothermal method. Single-crystal X-ray analysis revealed that it crystallized in orthorhombic system, Pnma space group. The supramolecular crystalline network is formed via intermolecular hydrogen bonds. The target product was characterized by Infrared spectrum, thermogravimetric-differentialthermal, cyclic voltammetry and fluorescent spectrum. Results prove that Complex emits blue fluorescence and has irreversible photochromic properties. Differential thermal-thermogravimetric and cyclic voltammetry shows that Complex has high thermal stability and strong oxidizability. The catalytic performances of Complex were investigated by solid-gas heterogeneous catalysis method. Using solid target product as catalyst, the catalyze degradation of methanol was tested in the temperature range from rt. to 160 °C. When the system flow rate is 5.0 mL min−1, initial concentration of methanol is 5.34 g m−3, reaction temperature is 150 °C, eliminating rate of methanol is 76%, those indicate that Complex has good catalytic activity.

In this paper, Na2Mn2(MoO4)3 doubgyle molybdate was prepared by sol-gel method to investigate the structural, morphological and optical properties. X-ray diffraction analysis showed that Na2Mn2(MoO4)3 crystallizes in the triclinic system in the P 1 ¯ group. The composition and morphology of the compound were checked by energy dispersive spectroscopy coupled with scanning electron microscope. Optical properties were analyzed by UV–Vis diffuse reflectance spectroscopy. The photocatalytic properties were evaluated by the degradation of methylene blue under natural sunlight and compared to Xe and UV lamps. The highest photodegradation efficiency (85.3%) was obtained for solar irradiation, therefore, Na2Mn2(MoO4)3 can be a potential photocatalyst for the removal of dye wastewater pollution driven by visible-light. The proposed mechanism of photodegradation in water involves creation of hydroxyl radicals and superoxide anions that attack the methylene blue molecules and decompose it to carbon dioxide and water.

Hydrothermal techniques have been used to prepare two new Cu(I)/Mo(VI)-oxide hybrids that represent a rare example of crystallization of both achiral (1) and chiral (2) polymorphic structures with the composition CuMoO3(p2c) (p2c ​= ​pyrazine-2-carboxylate). Their structures were characterized by single-crystal X-ray diffraction (1 - space group: P21/c, Z ​= ​4; a ​= ​8.4965(3) A, b ​= ​12.7471(5) A, c ​= ​7.2850(3) A), β ​= ​97.147(2)o, and 2 - P32, Z ​= ​3, a ​= ​7.6789(2) A, c ​= ​10.9164(5) A) and found to consist of highly-distorted MoO5N octahedra that are vertex-bridged to form -O-Mo-O-Mo-O- chains and connected to each other via the coordinating p2c ligands and Cu(I) cations. In the achiral structure of 1, the p2c ligands and Cu(I) cations are coordinated to a single side of the extended -O-Mo-O-Mo-O- chains. In the chiral structure of 2, by contrast, these coordinate via a helical-type arrangement down the 32 screw axis with a rotation of 120° between neighboring octahedra. The chiral polymorph is favored with higher pressure and exhibits a correspondingly higher density owing to the greater packing efficiency of the helical chains, with calculated densities (g cm−3) of 2.81 and 2.95 for 1 and 2, respectively. Both are found to have nearly identical band gaps of ~1.37 ​eV, which are significantly smaller than in other related Cu/Mo oxides . Density functional theory calculations show that 1 exhibits a slightly lower energy of ~89 ​meV per formula (or ~8.6 ​kJ ​mol−1) as compared to 2 and is thus energetically favored. Given the higher calculated energy of the chiral polymorph, 2, this suggests that the application of higher pressures can provide a convenient driving force for the crystallization of higher-density, helical-chain structures that are noncentrosymmetric.

Subsolidus phase relations in the M2MoO4–Sc2(MoO4)3–Hf(MoO4)2 (M ​= ​Li, K) systems have been studied by the method of “intersecting cuts”. No new triple molybdates have been identified in the Li2MoO4–Sc2(MoO4)3–Hf(MoO4)2 system and a new triple molybdate K5ScHf(MoO4)6 is formed in the K2MoO4–Sc2(MoO4)3–Hf(MoO4)2 system. The structure of K5ScHf(MoO4)6, have been determined in space group R 3 ‾ c through Rietveld analysis of X-ray powder diffraction data. The melting point of molybdate is 999 ​K. The compound has high ion conductivity (about 10−3 ​S ​cm−1).

Cs2[(AnO2)2(TO4)3] (where An ​= ​U, Np; T ​= ​S, Se, Cr, Mo) is a remarkable family of actinide-bearing compounds due to the surprising persistence of its structure type despite the substitutions in actinide and oxyanion sites. Cesium uranyl sulfate and selenate compounds have been analysed using high-temperature powder X-ray diffraction, Raman and luminescence spectroscopy techniques; in addition, high-temperature oxide-melt calorimetry studies had been carried out to derive the enthalpies of formation of both compounds. The crystal structures of all six known isotypic compounds have been compared to reveal specific geometric parameters, which results in differences of thermal behavior and spectra. Chemical alteration in the An and T sites results in changes of the Cs+ coordination environment, which in turn leads to an increase of its influence on the layered structural units and the stability of the structure itself. These substitution mechanisms may be regarded as an example of the chemical composition selectivity for the preparation of compounds with the desired properties.

Herein, we report a facile synthesis of bismuth molybdate (α-Bi2Mo3O12) nanoplates (NPs) via hydrothermal route and studied its gas sensing performance. The developed α-Bi2Mo3O12 was analyzed by various technique for structural and morphological studies. XRD analysis showed the monoclinic crystal structure of α phase of Bi2Mo3O12 with crystalline size 40 nm. The morphological features were studied using FE-SEM and FE-TEM, showed Bi2Mo3O12 nanoplates of thickness 20–25 nm and also showed the signs of variation with different hydrothermal reaction time. The chemical composition and their states were studied by XPS and EDAX analysis. The material was examined for gas sensing proficiency towards various reducing gases (acetone, ethanol, propanol, xylene, trimethylamine). Bi2Mo3O12 NPs corroborate good selectivity (78%) towards ethanol at an optimum operating temperature 325 °C with the response and recovery time, 1′54s and 8′30s, respectively. Furthermore, the sensor showed better reproducibility and stability in response to consecutive exposure of ethanol. The α-Bi2Mo3O12 has two acidic sites and one basic site, which excel the interactions and are responsible for better gas sensing performance.

The memory glass effect (MGE) describes the ability of some materials to recover the initial structure and crystallographic orientation after pressure-induced amorphization (PIA). In spite of numerous studies the nature and underlying mechanisms of this phenomenon are still not clear. Here we report investigations of MGE in β′-Eu{sub 2}(MoO{sub 4}){sub 3} single crystal samples subjected to high pressure amorphization. Using the XRD and TEM techniques we carried out detailed analysis of the structural state of high pressure treated single crystal samples as well as structural transformations due to subsequent annealing at atmospheric pressure. The structure of the sample has been found to be complex, mainly amorphous, however, the amorphous medium contains evenly distributed nanosize inclusions of a paracrystalline phase. The inclusions are highly correlated in orientation and act as “memory units” in the MGE. - Graphical abstract: Schematic representation of pressure-induced amorphization and “memory glass” effect in rare-earth molybdate single crystals. The XRD and TEM measurements have revealed the presence of the residual identically oriented paracrystalline nanodomains in the pressure-amorphized state. These domains preserve the information about initial structure and orientation of the sample. They act as memory units and crystalline seeds during transformation of the amorphous phase back tomore » the starting single crystalline one. - Highlights: • Pressure-amorphized Eu{sub 2}(MoO4){sub 3} single crystals were studied ex-situ by XRD and TEM. • Tiny residual crystalline inclusions were found in amorphous matrix of sample. • The inclusions keep in memory the parent crystal structure and orientation. • The inclusions account for “memory glass” effect in rare-earth molibdates.« less

A new triple molybdate Na25Cs8Fe5(MoO4)24 was synthesized using solid state reactions and studied with X-ray powder diffraction, second harmonic generation (SHG) technique, differential scanning calorimetry, Mossbauer and dielectric impedance spectroscopy. Single crystals of Na25Cs8Fe5(MoO4)24 were obtained and its structure was solved (the space group P 1 ¯ , a=12.5814(5), b=13.8989(5), c=28.4386(9) A, α=90.108(2), β=90.064(2), γ=90.020(2)°, V=4973.0(3) A3, Z=2, R=0.0440). Characteristic features of the structure are polyhedral layers composed of pairs of edge-shared FeO6 and (Fe, Na)O6 octahedra, which are connected by bridging МоО4 tetrahedra. The layers share common vertices with bridging МоО4 tetrahedra to form an open 3D framework with the cavities occupied by the Cs+ and Na+ cations. The compound undergoes first-order phase transformation at 642 K and above this phase transition, electrical conductivity reaches 10−3–10−2 S cm−1. Thus, Na25Cs8Fe5(MoO4)24 may be considered as a promising compound for developing new materials with high ionic conductivity.

A series of inorganic organic hybrid materials based on polyoxometalates(POMs), namely, [MII(HL)2(H2O)2][MoVI6O20] [M=Co (1), Ni (2), Cu (3), Zn (4)], [MnIVL2(H2O)2][MoVI6O20] (5), and (HL)3PMO12O40 (6) [L=3-(4-pyridyl)pyrazole], have been synthesized. The compounds have been characterized by elemental analysis, powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction. The results from single-crystal X-ray diffraction indicate that 1–5 are isostructural. It is worth noting that the polyanions are bridged by Mo–O–Mo to form 1D inorganic chains, which are further connected via M ions to form 2D nets. In compound 6, the ligands are used as the positive ions to balance the charge of the compound. Moreover, the magnetic properties of compound 5 have also been investigated in detail.

A new double molybdate Na9Fe(MoO4)6 was synthesized using solid state reactions and studied with X-ray powder diffraction, second harmonic generation (SHG) technique, differential scanning calorimetry, X-ray fluorescence analysis, Mossbauer and dielectric impedance spectroscopy. Single crystals of Na9Fe(MoO4)6 were obtained and its structure was solved (the space group R3, a¼14.8264(2), c ¼19.2402(3) A, V¼3662.79(9) A 3 , Z ¼6, R ¼0.0132). The structure is related to that of sodium ion

Rare earth ( R ) molybdate pyrochlores, R 2 Mo 2 O 7 , are of interest as frustrated magnets. Polycrystalline samples of Lu 2 Mo 2 O 7− x prepared at 1600 °C display a coexistence of cubic pyrochlore phases. Rietveld fits to powder neutron diffraction data and chemical analyses show that the miscibility gap is between a stoichiometric x =0 and an oxygen-deficient x ≈0.4 phase. Lu 2 Mo 2 O 7 behaves as a spin glass material, with a divergence of field cooled and zero field cooled DC magnetic susceptibilities at a spin freezing temperature T f =16 K, that varies with frequency in AC measurements following a Vogel–Fulcher law. Lu 2 Mo 2 O 6.6 is more highly frustrated spin glass and has T f =20 K.

X-ray investigation of solid state interaction of the components in the Li 2 MoO 4 –Rb 2 MoO 4 –Fe 2 (MoO 4 ) 3 system was carried out, and a subsolidus phase diagram of the said system was constructed. The subsystem Rb 2 MoO 4 –LiRbMoO 4 –RbFe(MoO 4 ) 2 was shown to be non-quasiternary. Formation of a novel triple molybdate LiRb 2 Fe(MoO 4 ) 3 was established, conditions of solid state synthesis and crystallization of the compound were found. Its crystal structure (orthorhombic, space group Pnma , Z =4, a =24.3956(6), b =5.8306(1), c =8.4368(2) A) represents a new structure type and includes infinite two-row ribbons {[Fe(MoO 4 ) 3 ] 3− } ∞ parallel to the b axis and composed of FeO 6 octahedra, terminal Mo(3)O 4 tetrahedra, and bridge Mo(1)O 4 and Mo(2)O 4 tetrahedra connecting two or three FeO 6 octahedra. The ribbons are connected to form 3D framework via corner-sharing LiO 4 tetrahedra. Rubidium cations are 11- and 13-coordinated and located in cavities of this heterogeneous polyhedral framework.

A novel method involving a molten Ga flux for the synthesis of diffraction quality crystals of the compound Cu{sub 3.82(1)}Mo{sub 3}O{sub 12}, a copper molybdate in the Lyonsite (α-Cu{sub 3}Fe{sub 4}(VO{sub 4}){sub 6}) family, has been developed. Single-crystal X-ray diffraction data have been collected. Cu{sub 3.82(1)}Mo{sub 3}O{sub 12} crystallizes in the space group P2{sub 1}2{sub 1}2{sub 1} with cell dimensions of a=4.9972(1) A, b=11.0259(3) A, and c=17.4912(5) A. Refinement of the resulting structure has enabled modeling of disorder in the channels of the structure and has indicated the localization of copper vacancies to these channel positions. Thermopower measurements indicate that Cu{sub 3.82(1)}Mo{sub 3}O{sub 12} is a rare and interesting example of a cation-deficient n-type material. - Graphical abstract: The unit cell of Cu{sub 3.82(1)}(MoO{sub 4}){sub 3} with displacement ellipsoids drawn at the 75% probability level. Cu is green, Mo is blue, O is red. Highlights: ► A repeatable method for the synthesis Cu{sub 3.82(1)}Mo{sub 3}O{sub 12} has been developed. ► Single crystals were formed from a polycrystalline sample through the use of a gallium flux. ► Thermopower measurements of Cu{sub 3.82(1)}Mo{sub 3}O{sub 12} show n-type behavior.

Alkaline earth metal molybdates are promising candidates as a host material for high efficiency narrow spectral emission phosphors. These phosphors could potentially be used for the fabrication of phosphor-converted light emitting diodes (pc-LEDs). Phosphor crystals of calcium molybdate doped with rare earth dopant Ln 3+ (Ln=Eu, Dy, Tb) grown using flux growth method have been shown to exhibit higher excitation efficiency than the powders synthesized by solid-state reaction process. Molybdenum (VI) oxide has been found to be a suitable flux for growing large size optically transparent high quality crystals at a temperature around 1100 °C. Using the excitation wavelengths of 465 nm, 454 nm and 489 nm for CaMoO 4 : Eu 3+ , CaMoO 4 : Dy 3+ and CaMoO 4 : Tb 3+ , respectively, intense emission lines at wavelengths of 615 nm, 575 nm and 550 nm were observed. The optimized doping concentrations of 12%, 2% and 5% for Eu 3+ , Dy 3+ and Tb 3+ , respectively, provided the highest luminescence intensity.

X-ray diffraction characterization of materials prepared by solid-state reactions in the ternary systems La 2 Mo 2 O 9 –Nd 2 W 2 O 9 –“Nd 2 Mo 2 O 9 ” and La 2 Mo 2 O 9 –Pr 2 W 2 O 9 –Pr 2 Mo 2 O 9 has shown that, in these systems, compounds isostructural with the oxygen ion conductor La 2 Mo 2 O 9 exist in wide single-phase regions. Partial tungsten substitution for molybdenum may yield stable Ln 2 Mo 2−2 x W 2 x O 9 compounds with the La 2 Mo 2 O 9 structure, where Ln is a rare-earth element different from lanthanum and praseodymium, e.g., neodymium. Tungsten also stabilizes Pr 2 Mo 2 O 9 , which otherwise decomposes above 700 °C. A series of continuous solid solution was found in the La 2 Mo 2 O 9 –Pr 2 Mo 2 O 9 system. Polymorphism of compounds existing in the above ternary systems was studied by differential scanning calorimetry. The conductivity of most of the compounds studied approaches that of lanthanum molybdate.

XRD study of solid-phase interaction in the Li2MoO4–K2MoO4–In2(MoO4)3 system was performed. The boundary K2MoO4–In2(MoO4)3 system is an non - quasibinary join of the K2O–In2O3–MoO3 system where a new polymolybdate K3InMo4O15 isotypic to K3FeMo4O15 was found. In the structure (а=33.2905(8), b=5.8610(1), c=15.8967(4) A, β=90.725(1)°, sp. gr. C2/c, Z=8, R(F)=0.0407), InO6 octahedra, Mo2O7 diortho groups and MoO4 tetrahedra form infinite ribbons {[In(MoO4)2(Mo2O7)]3−}∞ along the b-axis. Between the chains, 8- to 10-coordinate potassium cations are located. A subsolidus phase diagram of the Li2MoO4–K2MoO4–In2(MoO4)3 system was constructed and a novel triple molybdate LiK2In(MoO4)3 was revealed. Its crystal structure (a=7.0087(2), b=9.2269(3), c=10.1289(3) A, β=107.401(1)°, sp. gr. P21, Z=2, R(F)=0.0280) contains an open framework of vertex-shared MoO4 tetrahedra, InO6 octahedra and LiO5 tetragonal pyramids with nine- and seven-coordinate potassium ions in the framework channels.

Mixed metal oxides (MMOs) prepared by the mild thermal decomposition of layered double hydroxides (LDHs) differ in their reactivity on exposure to aqueous molybdate containing solutions. In this study, we investigate the reactivity of some T–Al containing MMOs (T=Co, Ni, Cu or Zn) towards the formation of layered transition metal molybdates (LTMs) possessing the general formula AT2(OH)(MoO4)2·H2O, where A=NH4+, Na+ or K+. The phase selectivity of the reaction was studied with respect to the source of molybdate, the ratio of T to Mo and the reaction pH. LTMs were obtained on reaction of Cu–Al and Zn–Al containing MMOs with aqueous solutions of ammonium heptamolybdate. Rehydration of these oxides in the presence of sodium or potassium molybdate yielded a rehydrated LDH phase as the only crystalline product. The LTM products obtained by the rehydration of MMO precursors were compared with LTMs prepared by direct precipitation from the metal salts in order to study the influence of preparative route on their chemical and physical properties. Differences were noted in the composition, morphology and thermal properties of the resulting products.

The role of charge density matching in the formation of templated molybdates under mild hydrothermal conditions was investigated through the use of a series of structurally related amines: piperazine, 1,4-dimethylpiperazine, 2,5-dimethylpiperazine and 2,6-dimethylpiperazine. A series of reactions was conducted in which the relative mole fractions of each component were fixed at 2.5 MoO3:1 amine:330 H2O:2 H2SO4 in order to isolate the effects of the amine, the only variation between reactions was the structure of the amine. Four distinct polyoxomolybdates anions were observed, ranging from zero-dimensional β-[Mo8O26]4− molecular anions to [Mo3O10]n2n− and [Mo8O26]n4n− chains and [Mo5O16]n2n− layers. The primary influence over the structure of the molybdate anion is charge density matching with the protonated amine, which was quantified through surface area approximations based upon both calculated molecular surfaces and polyhedral representations of each anion. Secondary influences include amine symmetry and hydrogen-bonding preferences. The synthesis and characterization of two new compounds are reported. Crystal data: [C6H16N2][Mo3O10]·H2O (1), triclinic, P-1 (no. 2), a=8.0973(7) A, b=8.8819(9) A, c=11.5969(11) A, α=71.362(9)°, β=82.586(8)°, γ=74.213(8)°, Z=2, R/Rw=0.0262/0.0564, and [C6H16N2]2[Mo8O26] (2), monoclinic, P21/n (no. 14), a=7.9987(11) A, b=12.5324(19) A, c=16.003(3) A, β=97.393(14)°, Z=2, R/Rw=0.0189/0.0454.

Red phosphors gadolinium tungstate and molybdate with the formula Gd(2−x)MO6:Eux3+ (M=Mo, W) were successfully synthesized by the solid-state reaction at 900 and 1300 °C for 4 h, respectively. The products were characterized by an X-ray powder diffractometer (XRD), TG–DSC, FT-IR, PL, UV–vis and SEM. Room-temperature photoluminescence indicated that the as-prepared Gd(2−x)MO6:Eux3+ (M=Mo, W) had a strong red emission, which is due to the characteristic transitions of Eu3+ (5D0→7FJ, J=0, 1, 2, 3, 4) for these phosphors. Meanwhile, the 5D0→7F2 is in the dominant position. The emission quantum efficiency of Eu3+ in the Gd(2−x)MO6:Eux3+ (M=Mo, W) system has been investigated. The XRD results indicate that both Gd2WO6 and Gd2MoO6 belong to the monoclinic system with space group C2/c [A. Bril, G. Blasse, J. Chem. Phys. 45 (1966) 2350–2356] and I2/a [A. Bril, G. Blasse, J. Chem. Phys. 45 (1966) 2350–2356], respectively. SEM images indicate that the shape of Gd1.96WO6:Eu0.043+ is aggregated small particles with a mean diameter of about 300 nm, and the shape of Gd1.96MoO6:Eu0.043+ is block-like structures.

Hydrothermal treatment of CuCl{sub 2}.2H{sub 2}O, MoO{sub 3}, and 3,4'-dipyridylketone (3,4'-dpk) in 1:1:2 mole ratio afforded the new mixed metal oxide phases [Cu{sub 2}(MoO{sub 4}){sub 2}(3,4'-dpk)(H{sub 2}O)] (1) or [Cu{sub 4}(3,4'-dpk){sub 4}(Mo{sub 8}O{sub 26})] (2), depending on the pH of the initial reaction mixture. Compound 1 possesses unique one-dimensional (1-D) [Cu{sub 2}(MoO{sub 4}){sub 2}(H{sub 2}O)]{sub n} ribbons constructed from the linkage of {l_brace}Cu{sup II}{sub 4}O{sub 6}{r_brace} tetrameric units through isolated [MoO{sub 4}]{sup 2-} tetrahedra. These ribbons in turn are connected into a two-dimensional (2-D) coordination polymer structure by tethering 3,4'-dpk ligands. Compound 2, containing monovalent copper ions, manifests an unprecedented 'X-rail' 1-D extended structure with (6{sup 2}8){sub 4}(6{sup 6}) topology formed from the bracketing of discrete [{beta}-Mo{sub 8}O{sub 26}]{sup 4-} anions by four [Cu{sup I}(3,4{sup '}-dpk)]{sub n}{sup n+} chains. The variable temperature magnetic susceptibility behavior of 1 was fit to a linear tetramer model, with g=2.03(3), J{sub 1}=25.8(7) cm{sup -1} and J{sub 2}=-46(1) cm{sup -1}. Antiferromagnetic inter-tetramer interactions (zJ'=-0.21(3) cm{sup -1}) were also evident. Crystallographic data: 1 monoclinic, P2{sub 1}/c, a=10.3911(11) A, b=6.9502(6) A, c=22.958(2) A, {beta}=100.658(7){sup o}, V=1629.5(3) A{sup 3}, R{sub 1}=0.1256, and wR{sub 2}=0.2038; 2 triclinic, P1-bar,a=10.9000(3) A, b=11.7912(4) A, c=13.5584(4) A, {alpha}=102.482(2){sup o}, {beta}=102.482(2){sup o}, {gamma}=117.481(2){sup o},more » V=1450.98(8) A{sup 3}, R{sub 1}=0.0428, and wR{sub 2}=0.0630. - Graphical abstract: [Cu{sub 2}(MoO{sub 4}){sub 2}(3,4'-dpk)(H{sub 2}O)] (1, 3,4'-dpk=3,4'-dipyridylketone) and [Cu{sub 4}(3,4'-dpk){sub 4}(Mo{sub 8}O{sub 26})] (2) have been prepared by hydrothermal methods. 1 possesses 1-D [Cu{sub 2}(MoO{sub 4}){sub 2}(H{sub 2}O)]{sub n} ribbons containing magnetically interacting {l_brace}Cu{sub 4}O{sub 6}{r_brace} tetramers. The ribbons are connected into 2-D by 3,4'-dpk ligands. The reduced phase 2 manifests an unprecedented 1-D 'X-rail' chain motif.« less

Yttrium molybdate (Y2Mo3O12) has been prepared by non-hydrolytic sol–gel chemistry. The phase evolution upon heating was investigated using in situ and ex situ heat treatments combined with powder X-ray diffraction. This method has led to the isolation of two orthorhombic phases with different atomic connectivity. Yttrium adopts 6- and 7-coordinate sites in the Pbcn and Pba2 structures, respectively. Cocrystallization of both phases was observed in a narrow temperature range, suggesting that crystallization kinetics play a major role in phase formation. It was found that the Pba2 phase is the stable polymorph below 550 °C, and converts to Pbcn at higher temperatures.

Two new organic–inorganic hybrid compounds of molybdenum(VI) (HDBU)3(NH4)[β-Mo8O26]·H2O 1 and (HDBU)4[δ-Mo8O26] 2 have been synthesized and characterized by elemental analyses, FT-IR and UV–vis spectroscopies, and single-crystal X-ray diffraction (at 293 and 100 K, respectively). Compound 1 is obtained at room temperature by adding 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) on aqueous molybdate solution at pH=5.7. Compound 2 is obtained hydrothermally from 1 (110 °C, 24 h, autogenous pressure). Compound 1 crystallizes in the triclinic crystal system, space group P 1 ¯ , with a=11.2492(9), b=14.1907(10), c=16.7498(10) A, α=80.993(4), β=72.272(6), γ=71.696(7)°, V=2412.5(3) A3 at T=20 °C and Z=2. The refinement of the structure leads to a residual factor R=0.0697 for 10234 independent observed reflections [I/σ(I)⩾2] and 623 parameters. Compound 2 crystallizes in the triclinic crystal system, space group P 1 ¯ , with a=11.3158(9), b=11.3773(8), c=13.2884(17) A, α=92.110(8), β=112.127(9), γ=117.581(7)°, V=1357.4(3) A3 at T=−173 °C and Z=2. The refinement of the structure leads to a residual factor R=0.0226 for 11812 independent observed reflections [I/σ(I)⩾2] and 354 parameters. The structure of 1 consists of β-[Mo8O26]4− anions with HDBU+ and NH4+ cations connected to the mineral parts by hydrogen bonds and the structure of 2 contains δ-[Mo8O26]4− anions with HDBU+ counter-cations. Both the thermal and chemical isomerizations of the two [Mo8O26]4− isomers are highlighted and discussed. Photochromic behaviors of compounds 1 and 2 are also reported.

Three new uranyl tungstates, A(8)[(UO(2))4(WO(4))(4)(WO(5))(2)] (A = Rb (1), Cs (2)), and Rb(6)[(UO(2))(2)O(WO(4))(4)] (3), were prepared by high-temperature solid-state reactions and their structures were solved by direct methods on twinned crystals, refined to R(1) = 0.050, 0.042, and 0.052 for 1. 2, and 3, respectively. Compounds 1 and 2 are isostructural, monoclinic P2(1)/n, (1): a= 11.100(7), b = 13.161(9), c = 25.018(17)angstrom, beta = 90.033(13)degrees, V = 3654(4)angstrom(3), Z = 8 and (2): a = 11.252(2)angstrom, b = 13.815(3)angstrom, c = 25.736(6)angstrom, beta = 89.988(2)degrees, V=4000.2(16)angstrom(3), Z=8. There are four symmetrically independent sites that form linear uranyl cations with rather distorted coordination in their equatorial planes. There are six W positions: W(l) and W(2) have square-pyramidal coordination (WO(5)), whereas W(3), W(4), W(5), and W(6) are tetrahedrally coordinated. The structures are based upon a novel type of one-dimensional (1D) [(UO(2))(4)(WO(4))(4)(WO(5))(2)](4-) chains, consisting of WU(4)O(25) pentamers linked by WO(4) tetrahedra and WO(5) square pyramids. The chains run parallel to the a-axis and are arranged in modulated pseudo-2D-layers parallel to (010). The A(+) cations are in the interlayer space between adjacent pseudo-layers and provide a 3D integrity of the structures. Compounds 1 and 2 are the first uranyl tungstates with 2/3 of W atoms in tetrahedral coordination. Such a high concentration of low-coordinated W(6+) cations is probably responsible for the ID character of the uranyl tungstate units. The compound 3 is triclinic, P1 a = 10.188(2), b = 13.110(2), c = 18.822(3)angstrom, alpha = 97.853(3), beta = 96.573(3), gamma = 103.894(3)degrees, V = 2388.7(6)angstrom(3), Z = 4. There are four U positions in the structure with a typical coordination of a pentagonal bipyramid that contain uranyl ions, UO(2)(2+) as apical axes. Among eight W sites, the W(1), W(2), W(3), W(4)2 W(5). and W(6) atoms are tetrahedrally coordinated, whereas the W(7) and W(8) cations have distorted fivefold coordination. The structure contains chains of composition [(UO(2))(2)O(WO(4))(4)](6-) composed of UO(7) pentagonal bipyramids and W polyhedra. The chains involve dimers of UO(7) pentagonal bipyramids that share common 0 atoms. The dimers are linked into chains by sharing corners with WO(4) tetrahedra. The chains are parallel to [-101] and are arranged in layers that are parallel to (111). The Rb(+) cations provide linkage of the chains into a 3D structure. The compound 1 has many structural and chemical similarities to its molybdate analog. Rb(6)[(UO(2))(2)O(MoO(4))(4)]. However, the compounds are not isostructural. Due to the tendency of the W(6+) cations to have higher-than-fourfold coordination, part of the W sites adopt distorted fivefold coordination, whereas all Mo atoms in the Mo compound are tetrahedrally coordinated. Distribution of the WO(5) configurations along the chain extension does not conform to its 'typical' periodicity. As a result. both the chain identity period and the unit-cell volume are doubled in comparison to the Mo analog, which leads to a new structure type. (c) 2006 Elsevier Inc. All rights reserved

The new pyrazine-pillared solids, AgReO 4 (C 4 H 4 N 2 ) ( I ) and Ag 3 Mo 2 O 4 F 7 (C 4 H 4 N 2 ) 3 (C 4 H 4 N 2 =pyrazine, pyz) ( II ), were synthesized by hydrothermal methods at 150 °C and characterized using single crystal X-ray diffraction ( I — P 2 1 /c , No. 14, Z =4, a =7.2238(6) A, b =7.4940(7) A, c =15.451(1) A, β =92.296(4)°; II — P 2 /n , No. 13, Z =2, a =7.6465(9) A, b =7.1888(5) A, c =19.142(2) A, β =100.284(8)°), thermogravimetric analysis, UV-Vis diffuse reflectance, and photoluminescence measurements. Individual Ag(pyz) chains in I are bonded to three perrhenate ReO 4 – tetrahedra per layer, while each layer in II contains sets of three edge-shared Ag(pyz) chains ( π – π stacked) that are edge-shared to four Mo 2 O 4 F 7 3– dimers. A relatively small interlayer spacing results from the short length of the pyrazine pillars, and which can be removed at just slightly above their preparation temperature, at >150–175 °C, to produce crystalline AgReO 4 for I , and Ag 2 MoO 4 and an unidentified product for II . Both pillared solids exhibit strong orange-yellow photoemission, at 575 nm for I and 560 nm for II , arising from electronic excitations across (charge transfer) band gaps of 2.91 and 2.76 eV in each, respectively. Their structures and properties are analyzed with respect to parent ‘organic free’ silver perrhenate and molybdate solids which manifest similar photoemissions, as well as to the calculated electronic band structures.

We have determined the crystal structure of the title compound, which has a triclinic cell with cell parameters of a=6.844A, b=6.933A, c=9.339A, {alpha}=76.617{sup o}, {beta}=84.188{sup o}, {gamma}=74.510{sup o} and space group P1-bar. The crystal structure suggests the chemical formula CoMoO{sub 4}.3/4H{sub 2}O. The structure consists of MoO{sub 4} tetrahedra and CoO{sub 6} octahedra, confirming the earlier X-ray absorption near-edge spectroscopic (XANES) investigation on the hydrate. The comparison of the crystal structures of the hydrate and the {alpha}-,{beta}-, and hp-phases shows that the hydrate exhibits metal cation coordinations similar to those of the {beta}-phase, but had arrangements of CoO{sub 6} and MoO{sub n} polyhedra similar to those of the hp-phase.

Three heterometallic 1-D polymers, [{Ni(1,10-phen)2(H2O)}2 {(Mo5O15)(4,4′-dbp)}·(5.75H2O)] (4,4′-dbp=O3PCH2C6H4C6H4CH2PO3) (1), [{Co(1,10-phen)2(H2O)}2 {(Mo5O15)(4,4′-dbp)}·(5.5H2O)] (2) and [{Ni(2,2′-bpy)3}{Ni(2,2′-bpy)2(H2O)} {(Mo5O15)(4,4′-dbp)}·(4.75H2O)] (3), have been synthesized under hydrothermal conditions. Their structures were determined by single crystal X-ray diffraction. The 1-D chains is constructed of [Mo5O15(4,4′-dbp)]4− units, which are further decorated and charge compensated by [M(1,10-phen)2] (M=Ni, Co) or [Ni(2,2′-bpy)2] subunits. The thermogravimetric analyses and magnetic properties of 1 and 2 were studied.

The solid hybrid material (H3/4pbpy)4[PMo12O40]·1.25H2O (1) (pbpy=5-phenyl-2-(4-pyridinyl)pyridine) has been prepared and characterized. A structural feature of compound 1 is that the polyoxometalate anions exhibit a one-dimensional inorganic double chain-like structure via weak interactions of O…O. The organic moiety exhibits regular packing with offset aromatic–aromatic interactions between the pbpys, leading to a compact supramolecular framework structure to accommodate the inorganic chains. Compound 1 was employed to fabricate the three-dimensional bulk-modified carbon paste electrode (1-CPE) to research on its electrochemistry properties. The results indicate that 1 retained Keggin molybdate anion electrocatalytic activities toward the reduction of chlorate, hydrogen peroxide and nitrite.

The structure of La 6 Mo 8 O 33 has been determined from a triple pattern powder diffraction analysis. Two high-resolution neutron diffraction patterns collected at 1.594 and 2.398 A and one X-rays were used. This molybdate crystallizes in a non-centrosymmetric monoclinic space group P 2 1 ( N °4), Z =2, a =10.7411(3) A, b =11.9678(3) A, c =11.7722(3) A, β =116.062 (1)°. La 6 Mo 8 O 33 is an unusual ordered defect Scheelite. Hence, it should be described with cation vacancies and an extra oxygen atom following the formula: La 6 □ 2 Mo 8 O 32+1 . This extra oxygen atom leads to a pyramidal environment, whereas the other molybdenum atoms present tetrahedral environment. A molybdenum tetrahedral is connecting to the pyramid, forming an [Mo 2 O 9 ] unit.

An unusual compound, [{Cu(2,2′–bpy)} 2 (tp)Mo 4 O 13 ] (tp=terephthalate) 1 , has been hydrothermally synthesized and structurally characterized by the elemental analyses, IR spectrum, X-ray photoelectron spectrum, TG analyses and the single crystal X-ray diffraction. The structure of 1 exhibits a layered network built up from bimetallic one-dimensional ribbons bridged by dicarboxylate ligands. Compound 1 represents the first hybrid molybdates composed of mixed organodiamine and dicarboxylate ligands. Crystal data for compound 1 : triclinic, space group P 1 , a =7.3748(15) A, b =9.9692(2) A, c =12.0692(2) A, α =69.223(3)°, β =76.123(3)°, γ =76.623(3)°; V =794.83(3) A 3 ; Z =1, R (final)=0.0688. The data were collected on a Rigaku R-AXIS RAPID IP diffractometer at 293 K using graphite-monochromated Mo K α radiation ( λ =0.71073 A) and oscillation scans technique in the range 1.83° θ

Hydrothermal synthesis in the K–Mo oxide system was investigated as a function of the pH of the reaction medium. Four compounds were formed, including two K2Mo4O13 phases. One is a new low-temperature polymorph, which crystallizes in the orthorhombic, space group Pbca, with Z=8 and unit cell dimensions a=7.544(1) A, b=15.394(2) A, c=18.568(3) A. The other is the known triclinic K2Mo4O13, whose structure was re-determined from single crystal data; its cell parameters were determined as a=7.976(2) A, b=8.345(2) A, c=10.017(2) A, α=107.104(3)°, β=102.885(3)°, γ=109.760(3)°, which are the standard settings of the crystal lattice. The orthorhombic phase converts endothermically into triclinic phase at ca. 730 K with a heat of transition of 8.31 kJ/mol.

Pyrolysis of rare earth (R) polyoxomolybdate, [R2(H2O)12Mo8O27]·xH2O (R=La, Nd and Sm), at 750°C for 2–8 h results in crystallization of R2Mo4O15 compounds. β-La2Mo4O15 crystallizes together with an α-form in monoclinic P21/a (No. 14), a=13.8893(5), b=13.0757(4), c=20.0927(8) A, β=95.199(2)°, V=3634.1(2) A3, Z=12, R1(I>2σ(I))=0.048, Rw (all data)=0.116. The structure is built up with {LaOn} (n=9, 10) and {MoOn′} (n′=4–6) polyhedral units. The {LaOn} units are polymerized into a linear {La6O39}∞ chain, while the {MoOn} are connected together to form {Mo4O15} and {Mo7O26} groups. The structure can be related to the α-form by partial rearrangement of O atoms and small shifts of La and Mo atoms. The R2Mo4O15 (R=Nd and Sm) compounds are isomorphous with the previously reported R=Eu and Gd analogs, crystallizing in triclinic, P 1 (No. 2), a=9.4989(5) and 9.4076(7), b=11.0088(7) and 10.9583(8), c=11.5665(6) and 11.5234(8) A, α=104.141(3) and 104.225(3), β=109.838(3) and 109.603(3), γ=108.912(3) and 108.999(3)°, V=987.3(1) and 970.5(1) A3, Z=3, R1(I>2σ(I))=0.028 and 0.030, Rw (all data)= 0.079 and 0.094, respectively. The crystal structure is composed of {RO8} and {MoOn′} (n′=4–6) polyhedral units. The molybdate units are condensed to give a corrugated {Mo4O17}∞ chain. The square-antiprismatic {RO8} units share their trigonal and square faces, forming {R2O13} and {R2O12} groups, respectively. A very short R⋯R distance (3.557(6) A for R=Nd; 3.4956(6) A for R=Sm) is achieved in the latter unusual {R2O12} group. A common cationic arrangement was found in all the structures in the R2Mo4O15 family: a R–R pair with the shortest separation and surrounding 12 Mo atoms. The symmetry of the cationic arrangement was reduced with an increase of atomic number of R, viz. La>Ce, Pr>Nd–Gd≈Tb, Ho.

Two new mixed organic–inorganic uranyl molybdates, (C 6 H 14 N 2 ) 3 [(UO 2 ) 5 (MoO 4 ) 8 ](H 2 O) 4 ( 1 ) and (C 2 H 10 N 2 )[(UO 2 )(MoO 4 ) 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) A, α =96.734(2)°, β =91.107(2)°, γ =110.193(2)°, V =1659.1(2) A] has been solved by direct methods and refined on the basis of F 2 for all unique reflections to R 1=0.058, which was calculated for the 5642 unique observed reflections (| F o |⩾4 σ F ). The structure contains topologically novel sheets of uranyl square bipyramids, uranyl pentagonal bipyramids, and MoO 4 tetrahedra, with composition [(UO 2 ) 5 (MoO 4 ) 8 ] 6− , that are parallel to (−101). H 2 O 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) A, α =86.112(1)°, β =86.434(1)°, γ =76.544(1)°, V =1203.14(10) A] has been solved by direct methods and refined on the basis of F 2 for all unique reflections to R 1=0.043, which was calculated for 5491 unique observed reflections (| F o |⩾4 σ F ). The structure contains topologically novel sheets of uranyl pentagonal bipyramids and MoO 4 tetrahedra, with composition [(UO 2 )(MoO 4 ) 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.

A novel compound [Cu(en)2]4[SiMo8VV4O40(VIVO)2][MoO4]2·5H2O has been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Black crystals crystallize in the tetragonal system, space group I4/m, a=b=14.019(2) A, c=20.341(4) A, V=3997.9(11) A3, Z=2, λ(MoKα)=0.71073 A (R(F)=0.0443 for 1819 reflections). Data were collected on a Siemens P4 four-circle diffractometer at 293 K in the range of 1.76

An interesting structural transformation from a two dimensional (2d) covalent oxide network with a layered structure to a three-dimensional (3d) network with a tunnel structure was found at room temperature in the mixture of hydrated alkali-metal molybdenum bronze and amorphous alkali-metal molybdate. From various experimental results it was concluded that the transformation was due to a room temperature solid state reaction.