Mo 2O Research Articles

Determination of thiamazole in pharmaceutical samples by phosphorus molybdenum blue spectrophotometry

A novel method is established to determine thiamazole by phosphorus molybdenum blue spectrophotometry. The experiment indicates that PO 4 3− reacts with Mo 7O 24 6− in 0.30 mol/L H 2SO 4 solution to form a product with phosphorus–molybdenum heteropoly acid ([H 2PMo 12O 40] −). Then [H 2PMo 12O 40] − is deoxidized to form phosphorus molybdenum blue (H 3PO 4·10MoO 3·Mo 2O 5) by thiamazole. The amount of thiamazole can be determined based on the absorbance of phosphorus molybdenum blue ( λ max = 710 nm). A good linear relationship is obtained between the absorbance and the concentration of thiamazole in the range of 0.035–70 μg/mL. The equation of the linear regression is A = 0.03384 + 0.00834 c (μg/mL), with a linear correlation coefficient of 0.9990. The apparent molar absorption coefficient is 1.0 × 10 3 L/(mol cm). The method has been successfully applied to the determination of thiamazole in pharmaceutical samples with satisfactory results, and recoveries are in the range of 99.6–100.6%.

Anomaly diffuse and dielectric relaxation in strontium doped lanthanum molybdate

The dielectric properties of the La 2− x Sr x Mo 2O 9− δ ( x = 0–0.2) ceramics were investigated in the temperature range of 300–800 K. Dielectric measurement reveals that two dielectric anomalies, associated with the oxygen ion diffusion, exist in frequency spectrum with x = 0.5. The broad dielectric peaks in tan δ( ω) can be well fitted by a modified Cole–Cole approach. When x = 0.1, only one dielectric relaxation peak is observed, corresponding to different oxygen ion diffusion processes, as distinct from the only relaxation peak in the pure La 2Mo 2O 9. The relaxation parameters τ 0, the dielectric relaxation strength Δ, and the activation energy E a were obtained. The result of this work shows that, the conductivity change caused by doping between the two phases is due to the combination of the dipolar effects and motion of ions.

Thermal spreading of MoO 3 in H–ZY

This work provides a structural, optical and kinetics approach to the molybdenum oxo-species formed during thermally driven migration on H–ZY starting from mechanical mixtures with MoO 3. The samples were characterized as a function of time of treatment by UV–vis diffuse reflectance, X-ray diffraction, N 2 adsorption and scanning transmission electron microscopy (STEM). Local analysis of elemental compositions obtained from linear scan of characteristic X-ray signal show a direct evidence of molybdenum presence into the zeolite crystals. Ultraviolet absorption spectra were used to determine both the kinetics of the spreading and the speciation of MoO x in the H–ZY. Besides MoO 3, three surface molybdenum oxo-species were identified according to the edge energy ( E g) values of bulk molybdenum oxide reference compounds. This study shows that the tetrahedral species prevailed on H–ZY. This is consistent with limitations in the migration and growth of MoO x in the channel structure of the zeolite. Kinetic study suggest that migration of MoO x in the H–ZY at low temperature (ca. 723 K) occurs across the formation and diffusion of hydrated species such as MoO 2(OH) 2, which interact with the zeolite and form monomeric and dimeric structures (like (MoO 4) 2− and (Mo 2O 7) 2−). Migration of MoO x species in the H–ZY studied is significant even at 723 K and after very short periods of treatment (<5 min).

Enhanced red luminescence of Eu 3+ and R 3+ -doped La 2Mo 2O 9 phosphors under blue light excitation

The red phosphors La 2− x− y Eu x R y Mo 2O 9 ( x = 0.6, y = 0–0.07, R = Gd, Dy, Y and Yb) were prepared by solid-state reactions, and their photoluminescent properties were investigated. Under the excitation of 465 nm blue light, the red emission around 615 nm originating from the 5D 0 → 7F 2 transition of Eu 3+, is obviously shown in these phosphors. After the co-doping of small amounts of rare earth (Gd, Dy, Y and Yb) ions with Eu 3+, the emission intensity of phosphors is effectively enhanced. In particular, the La 1.37Eu 0.6Yb 0.03Mo 2O 9 sample exhibits the strongest emission intensity (about 160% as compared with that of La 1.4Eu 0.6Mo 2O 9 sample) due to the addition of Yb 3+ with relative smaller ionic radius. This is a welcome change for the red phosphor used in white light-emitting diodes.

Structural properties of molybdenum-lead-borate glasses

Glasses and glass ceramics in the system xMoO 3·(100 − x)[3B 2O 3·PbO] with 0 ≤ x ≤ 30 mol% have been prepared from melt quenching method and characterized by means of X-ray diffraction, FTIR, UV–VIS and EPR spectroscopy. We have examined and analyzed the effects of systematic molybdenum ions intercalation on lead-borate glasses and glass ceramics with interesting results. The observations present in these mechanisms show the lead ions bonded ionic have a strong affinity towards [BO 3] units containing non-bridging oxygens and [MoO 4] 2− molybdate units. The pronounced affinity towards molybdate anions yields the formation of the PbMoO 4 crystalline phase. Then, the excess of oxygen can be supported into the glass network by the formation of [MoO 6] and [Mo 2O 7] structural units. Pb 2+ ions with 6s 2 configuration show strong absorption in the ultraviolet due to parity allowed s 2–sp transition and yield an absorption band centered at about 310 nm. The changes in the features of the absorption bands centered at about 310 nm can be explained as a consequence of the appearance of additional absorption shoulder due to photoinduced color centers in the glass such as the formation of borate-molybdate and lead-molybdate paramagnetic defect centers in the glasses. The concentration of molybdenum ions influences the shape and width of the EPR signals located at g ∼ 1.86, 1.91 and 5.19. The microenvironment of molybdenum ions in glasses is expected to have mainly sixfold coordination. However, there is a possibility of reduction of a part of molybdenum ions from the Mo 6+ to the Mo 5+ and Mo 4+ to the Mo 3+ states.

Hydrated {Mo 72Fe 30} clusters: Low-frequency hydrogen modes and self-aggregation

Using incoherent quasi-elastic and inelastic neutron scattering, we have investigated the hydrogen relaxational dynamics and hydrogen vibrational modes in the polyoxomolybdate specie [Mo 72Fe 30O 252(CH 3COO) 12[Mo 2O 7(H 2O)] 2[H 2Mo 2O 8(H 2O)](H 2O) 91]· ≈ 150 H 2O. The translational dynamics of the water molecules in the compound is profoundly different from that of bulk water at the same temperature showing a non-Debye relaxation behavior. The temperature dependence of the relaxation time can be described in terms of an Arrhenius law, indicating that the dynamics is triggered by the breaking of the bonds connecting the crystal water molecules with the hydrophilic nanocapsule surfaces. Inelastic neutron scattering spectra confirm the attenuation of water translational modes with respect to the bulk water case due to the strong destructuring effect imposed by the nanocage interface and the enhancement of the highest frequency librational mode as already found in hydrated Vycor or Gelsil matrix. Small angle X-ray scattering on freshly prepared aqueous solution evidences the presence of nanocapsule structures proper of the monomer (2.6 nm in diameter) that coexist with a small amount of oligomers. After 1 month the polyoxomolibdate specie self-assembles in a supramolecular structure with a polydisperse distribution of dimensions spanning from the monomer to the “blackberry” vesicular structure already reported in literature.

Synthesis and characterisation of dinuclear oxomolybdenum(V) complexes with thienyl carboxylate ligands

The first structurally characterised oxomolybdenum(V) complexes with thienyl carboxylate ligands were prepared by the reaction of [Mo 2O 3(C 5H 7O 2) 4] or (NH 4) 2[MoOCl 5] with the corresponding acid (2-thiophenecarboxylic, 5-methyl-2-thiophenecarboxylic or 3-(3-thienyl)acrylic acid). Complexes [Mo 2O 3(μ-OC 2H 5)(μ-O 2CR)(C 5H 7O 2) 2](R = –C 4H 3S ( 1), –C 4H 2S(CH 3) ( 2) or –CH CHC 4H 3S ( 3)) were obtained upon substitution of two acetylacetonate ligands from [Mo 2O 3(C 5H 7O 2) 4] with RCOO − in dry ethanol. Reactions of (NH 4) 2[MoOCl 5] with the corresponding thienyl carboxylic acid in the presence of γ-picoline (C 6H 7N) yielded complexes (C 6H 7NH)[Mo 2O 4(μ-O 2CR)Cl 2(C 6H 7N) 2] (R = –C 4H 3S ( 4), –C 4H 2S(CH 3) ( 5) or –CH CHC 4H 3S ( 6)). All of the six new complexes were characterised as dinuclear. The molecular structures of 1, 3, 4· 0. 5CH 3CN and 5 were determined by the single crystal X-ray diffraction method. In the complexes the two molybdenum atoms are doubly bridged either by one oxygen and one ethoxy-oxygen, or alternatively by two oxo-oxygens, and are additionally bridged by the thienyl carboxylate ion in a didentate bridging manner. All complexes were further characterised by means of chemical analysis, IR spectroscopy, TG and in some cases by the one and two-dimensional NMR method.

Selective synthesis of triangular cluster oxido-sulfidocomplexes of Mo and W: High yield preparations of [Mo 3O 2S 2(H 2O) 9] 4+, [W 3O 2S 2(H 2O) 9] 4+, [W 2MoO 2S 2(H 2O) 9] 4+ and their derivatization

Reaction of [Mo 2O 2(μ-S) 2(H 2O) 6] 2+ with Mo(CO) 6 or metallic Mo under hydrothermal conditions (140 °C, 4 M HCl) gives oxido-sulfido cluster aqua complex [Mo 3(μ 3-S)(μ-O) 2(μ-S)(H 2O) 9] 4+ ( 1). Similarly, [W 3(μ 3-S)(μ-O) 2(μ-S)(H 2O) 9] 4+ ( 2) is obtained from [W 2O 2(μ-S) 2(H 2O) 6] 2+ and W(CO) 6. While reaction of [Mo 2O 2(μ-S) 2(H 2O) 6] 2+ with W(CO) 6 mainly proceeds as simple reduction to give 1, [W 2O 2(μ-S) 2(H 2O) 6] 2+ with Mo(CO) 6 produces new mixed-metal cluster [W 2Mo(μ 3-S)(μ-O) 2(μ-S)(H 2O) 9] 4+ ( 3) as main product. From solutions of 1 in HCl supramolecular adduct with cucurbit[6]uril (CB[6]) {[Mo 3O 2S 2(H 2O) 6Cl 3] 2CB[6]}Cl 2⋅18H 2O ( 4) was isolated and structurally characterized. The aqua complexes were converted into acetylacetonates [M 3O 2S 2(acac) 3(py) 3]PF 6 (M 3 = Mo 3, W 3, W 2Mo; 5a– c), which were characterized by X-ray single crystal analysis, electrospray ionization mass spectrometry and 1H NMR spectroscopy. Crystal structure of (H 5O 2)(Me 4N) 4[W 3(μ 3-S)(μ 2-S)(μ 2-O) 2(NCS) 9] ( 6), obtained from 2, is also reported.

A density functional theory study of multioxomolybdenum(VI) compounds [Mo 2O 6(imi) 6] (imi = imidazole) and Mo 2O 6: Structure, bonding, and properties

Two dinuclear multioxomolybdenum(VI) compounds containing rare trans-configuration O–Mo–O groups, [Mo 2O 6(imi) 4] ( 1) (imi = imidazole) and Mo 2O 6, have been investigated by the density functional theory level (DFT) calculation. The geometrical structure, electronic structure, and bonding properties of important Mo–ligand interactions (including Mo–O (terminal), Mo–O (bridging) and Mo–N (imi)) have been analyzed detailedly. Moreover, the influence of weak imi subgroup on the Mo 2O 6 core in 1 has been examined by the Mulliken population analysis (MPA), and the partial states of density (PDOS) and the overlap population density of states (OPDOS) analyses. The bond strength and covalency in them are in an order of Mo–O (terminal) > Mo–O (bridging) > Mo–N (imi). The introduction of imi ligand results in significant weakness of important Mo–ligand interactions, implying that the catalytic reactivity of such compounds in organic reactions can be suitably tuned by ligation of N-donor ligand to multioxomolybdenum(VI) core.

Structural and electrical properties of La 2− xBa xMo 2O 9− x/2 ( x = 0–0.18)

La 2− x Ba x Mo 2O 9− x/2 ( x ≤ 0.18) have been prepared by solid state reaction method. The lattice parameter of La 2− x Ba x Mo 2O 9− x/2 ( x ≤ 0.18) determined by XRD data refinement shows a linear dependence on the dopant Ba content x. For the specimen with a La/Ba molar ratio of 0.18–0.2, additional reflection of secondary phase exists in the XRD pattern, so the value of solubility limit for Ba in La 2Mo 2O 9 is defined in range of 0.18 < x < 0.2. As the replacement degree of La 3+ by Ba 2+ increases, the bulk conductivity of La 2− x Ba x Mo 2O 9− x/2 ( x ≤ 0.18) decreases initially and then increases, a minimum value at La 1.9Ba 0.1Mo 2O 8.95 exists. Hebb–Wagner studies in argon atmosphere, which use an oxide-ion blocking electrode, show that La 2− x Ba x Mo 2O 9− x/2 ( x ≤ 0.18) are predominantly oxide-ion conducting in the temperature ranging from 773 to 1173 K. The average thermal expansion coefficient of La 1.84Ba 0.16Mo 2O 8.92 determined by high-temperature XRD was deduced as great as 17.5 × 10 −6 K −1 between 298 and 1173 K.

Coordination chemistry of copper-molybdates with alkoxide ligands: The {Mo 4O 10(OMe) 6} 2− and [Mo 2O 4{RC(CH 2O) 3} 2] 2− clusters as building blocks

The reactions of the Keplerate super cluster [Mo 132O 372(CH 3CO 2) 30(H 2O) 72] 42− with a Cu(II) source and an organonitrogen donor in methanol/DMF solutions yielded a series of bimetallic organic–inorganic oxide hybrid materials, including the molecular species [Cu(phen) 2MoO 4] ( 1) and [{Cu(terpy)} 2(MoO 4) 2] ( 2) and a series of materials constructed from the tetranuclear building block {Mo 4O 10(OMe) 6} 2−: the molecular [{Cu 2(phen) 2(O 2CCH 3) 2 (MeOH)}Mo 4O 10(OMe) 6] ( 3), [{Cu(terpy)(O 2CCH 3)} 2Mo 4O 10(OMe) 6] ( 4) and [{Cu(terpy)Cl} 2Mo 4O 10(OMe) 6] ( 5), the one-dimensional phases [{Cu(bpy)(HOMe) 2}Mo 4O 10(OMe) 6] ( 6), [{Cu(bpy)(DMF) 2}Mo 4O 10(OMe) 6] ( 7), [{Cu(bpa)(DMF) 2}Mo 4O 10(OMe) 6] ( 8), [{Cu(phen)(DMF) 2}Mo 4O 10(OMe) 6] ( 9) and [{CuCl(dpa)} 2Mo 4O 10(OMe) 6] ( 10), and the two-dimensional material [{Cu 2(DMF) 2(pdpa)}{Mo 4O 10(OMe) 6} 2] ( 11). When methanol is replaced by the tridentate alkoxide tris-methoxypropane (trisp), the {Mo 2O 4(trisp) 2} 2− cluster building block is observed for [Cu(phen)Mo 2O 4(trisp) 2] ( 12), [Cu(bpa)(DMF)Mo 2O 4(trisp) 2] ( 13) and [{Cu(bpy)(NO 3)} 2Mo 2O 4(trisp) 2] ( 14).

Synthesis, characterization and spectroscopic study of riboflavin–molybdenum complex

A riboflavin–molybdenum [(RF)–Mo(V)] complex in powder form was synthesized and characterized by elemental analysis, UV–Vis, IR, NMR spectroscopy and X-ray diffraction. During the synthesis of this metal complex, another metal complex [Mo 2O 4(H 2O) 6] 2+ was also synthesized and characterized. The results of X-ray diffraction study have revealed an orthorhombic cubic system for the RF–Mo complex. The steady state absorption and emission studies of RF and RF–Mo in hydrochloric acid (HCl) of varying pH were investigated. The steady state absorption with RF–Mo showed distinct changes in the absorption spectra of RF after complexation. The steady state emission results, consistent with prior reports showed fluorescence quenching in the aqueous solution of both RF and RF–Mo in HCl with the proton acting as a quencher. The Stern–Volmer constant observed was 108.79 and 98.68 for RF and RF–Mo, respectively. The binding constant for RF–Mo complex was found to be 1.201 × 10 3 M −1 at 298 K.

Cathodic electrodeposition of mixed molybdenum–selenium oxides

Molybdenum–selenium oxides were electrochemically deposited onto indium–tin oxide (ITO) coated glass substrates from aqueous solutions containing molybdate ( Mo VI O 4 2 - ), selenate ( Se IV O 3 2 - ), and dimeric and tetrameric peroxo-polymolybdate (i.e., [Mo 2O 3(O 2) 4(H 2O) 2] 2−, [Mo 4O 9(O 2) 4] 2−) anions. Electrodeposition mechanisms were elucidated using chronocoulometry, cyclic voltammetry, spectroelectrochemistry, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and electrochemical quartz crystal nanogravimetry (EQCN). At relatively positive deposition potentials from −0.1 V to −0.4 V (versus Ag/AgCl) a substoichiometric molybdenum oxide phase, Mo 3O 8, co-deposits with an insulating phase of Se 0. At more negative potentials, mixed molybdenum–selenium oxides (Mo x Se 1− x O y , 0 < x < 0.4) are deposited. Competing side reactions involving hydrogen and hydrogen selenide influence the structure, composition, and morphology of the mixed molybdenum–selenium oxide deposits.

Synthesis of Cu(I) octamolybdates using tetrakis-acetonitrilecopper(I) hexafluorophosphate

Reaction of (NBu 4) 2[Mo 2O 7] with [Cu(CH 3CN) 4](PF 6) in acetonitrile results in isolation of the orange β-octamolybdate [Cu(CH 3CN) 4] 2[Mo 8O 26Cu 2(CH 3CN) 4] ( 1) along with the colourless α-octamolybdate [Cu(CH 3CN) 4] 4[Mo 8O 26]·2CH 3CN ( 2). Both products decompose rapidly upon removal from their mother liquors, forming an insoluble, dark brown coloured phase with the composition Cu 4[Mo 8O 26]·0.6CH 3CN·16H 2O ( 3). The copper(I) acetonitrile derivatised isopolyanion in 1 thus represents an intermediate structure between the simple, underivatised octamolybdate 2 and fully condensed, polymeric phase 3.

First principle study of structural, phase stabilization and oxygen-ion diffusion properties of β-La 2 − xL xMo 2O 9 (L = Gd, Sm, Nd and Bi) and β-La 2Mo 2 − yM yO 9 (M = Cr, W)

We have performed a first principle study of structural and phase stabilization of β-La 2 − x L x Mo 2O 9 (L = Gd, Sm, Nd and Bi) and β-La 2Mo 2 − y M y O 9 (M = Cr, W). The substitutional-site properties were discussed in terms of the empirical parameter, bond valence sums (BVS), which characterizes the interactions between atoms and its nearest-neighbor atoms and correlates well with the stability of the structure. We found that Gd, Sm and Nd atoms prefer the crystallographic sites with largest BVS values. The nonlinear dependence of cell parameter on W content in W-doped systems results from the nonlinear change in Mo/W–O bond length with W content. The decrease of cohesive energy and the deviation of BVS values from the expected values upon the Gd, Sm, Nd and W-doped concentration help us understand the experimentally observed stabilization of the β phase to lower temperatures in these doped system. The O ion diffusion properties in W-doped systems have been studied using the nudged elastic band method and the dimer method. We found that, W-doping leads to the obvious increase in the energy barriers of O ion concerted diffusion. In addition, there is a remarkable decrease in the difference of energy barriers between two diffusion channels involving O(1) ion, which sheds light on only one relaxation peak in the mechanical relaxation measurement in W-doped system, compared to undoped system.

En route to {Mo 2O 2(μ 2-O) 2} 2+ species: Isolation and structural characterization of a novel methoxide-bridged Mo(V) complex

Reaction of a mononuclear [MoOCl 4(H 2O)] − with pyridinium acetate in methanol leads to formation of an unusual complex, (PyH) 2[Mo 2O 3(OMe)(OOCCH 3)Cl 4]. Instead of the common dioxide-bridged structure, the anionic complex features a pair of metal centres bridged by oxide, methoxide and acetate. The Mo−Mo bond distance is 2.6390(2) Å. The intermediate nature of this triply-bridged species was shown by its reactions with pyridine and methanol which afforded stable {Mo 2O 2(μ 2-O) 2} 2+ species.

Phase stability of Keplerate-type polyoxomolybdates controlled by added cationic surfactant

Phase stability of two nanometer-scale Keplerate-type polyoxomolybdates, (NH 4) 42[Mo VI 72Mo V 60O 372(CH 3COO) 30(H 2O) 72]⋅300H 2O⋅10CH 3COONH 4 ({Mo 132}) and Mo VI 72Fe III 30O 252L 102⋅ca. 180H 2O with L = H 2O/CH 3COO −/Mo 2O n− 8/9 ({Mo 72Fe 30}), can be easily achieved by controlling the concentration of a cationic surfactant, tetradecyltrimethylammonium bromide (TTABr), in aqueous solution. Precipitates and floccules were observed when the stoichiometric ratios of r TTA + / { Mo 132 } and r TTA + / { Mo 72 Fe 30 } were 40:1 and 90:1, respectively, which were determined by zeta potential measurements. The surface charge properties and structure morphologies of {Mo 132} and {Mo 72Fe 30} induced by controlling cationic TTABr in aqueous solution were determined by zeta potential measurements and transmission electron microscopy (TEM) observations. {Mo 132} and {Mo 72Fe 30} can self-assemble into supramolecular “Blackberry” structures and exist at compositions less than the stoichiometric ratios of r TTA + / { Mo 132 } and r TTA + / { Mo 72 Fe 30 } in aqueous solution. Above the 1:1 stoichiometric ratio of TTABr/{Mo 132} or TTABr/{Mo 72Fe 30}, the precipitates and floccules dissolve. Dynamic laser light scattering (DLS) measurements clearly demonstrated that the R h values have essentially no angular dependence at excess amounts of TTABr, suggesting the presence of spherically symmetric aggregates of {Mo 132} and {Mo 72Fe 30}. Bilayer-like structures in aqueous solution were also demonstrated by TEM images. The interesting phase transition observed in our model systems of {Mo 132} and {Mo 72Fe 30} macroanions with high chemical stability, similar shape, and masses could provide models for the understanding of more complex polyelectrolyte solutions and self-assembled soft magnetic materials and in bioapplications for highly selective adsorbents of proteins with different molecular sizes and charges.

Molybdenum(VI) complexes of a few pyrimidine derived ligands and the study of metal mediated C [dbnd]N bond cleavage resulting in ligand transformation during complex formation

The syntheses of dioxomolybdenum(VI) complexes were attempted using the Schiff base ligands HL 1 and HL 2. The ligands were prepared by the condensation of 4,6-dimethyl 2-hydrazino pyrimidine with salicyl aldehyde (for HL 1) and o-hydroxy acetophenone (for HL 2). When MoO 2(acac) 2 was used as a metal precursor, HL 1 yielded the normal ligand exchange product [MoO 2(L 1)Cl] ( 1) in a medium acidified by HCl. However, instead of the normal product, HL 2 produced two bis chloro dioxomolybdenum(VI) complexes [MoO 2(L 3)Cl 2] ( 2) and [Mo 2O 5(L 3)Cl 2] ( 3) in the same reaction medium. Here, L 3 is a bidentate neutral ligand 2-(3,5-dimethyl-1-pyrazolyl) 4,6-dimethyl pyrimidine, which is afforded by a transformation of the used ligand. This ligand transformation reaction is probably triggered by molybdenum mediated C N bond cleavage in the hydrazone part of HL 2 followed by cyclization with acetylacetone released from the metal precursor. Again, when MoO 2(acac) 2 was reacted with another related ligand H 2 L 1 ′ , a bis salicyl hydrazone of 2,4-dihydrazino pyrimidine, in acidic medium, [MoO 2(L 4)Cl] ( 4) was produced as the only product. Here, also a similar ligand transformation, but only to a partial extent, leads to the formation of the ligand HL 4, the salicyl hydrazone of 2-hydrazino-4-(3,5-dimethyl-1-pyrazolyl) pyrimidine. HL 4, thus produced in the reaction medium binds in a monoanionic fashion to the MoO 2 2+ core to form the complex [MoO 2(L 4)Cl] ( 4). The complexes are characterized by elemental analyses, electronic spectra, IR, 1H NMR, magnetic measurements, EPR and by cyclic voltammetry. Complexes 1, 2, 3 and 4, as well as the ligand HL 2, have been crystallographically characterized in order to probe into the structures and the ligand transformation process in a comprehensive way.

Structure and reducibility of titania-supported monomeric and dimeric molybdenum oxide entities studied by DFT calculations

Molybdenum oxide deposited on anatase can be used to catalyse mild oxidation of hydrocarbons or alcohols. The nature of the active site is still under debate even if the catalytic activity has been related to the reducibility of the deposited phase. After the determination of MoO 3 and Mo 2O 6 adsorption geometries, we have investigated, by DFT calculations, the effect of the molecularity on the molybdenum reducibility. In dehydrated conditions, the monomeric species is in a rigid tetrahedral geometry and is less reducible than the support. Because of the interaction with the support’s surface, the molybdenum atoms in a dimeric specie are not in a regular tetrahedral environment. This distorted geometry allows an important reconstruction upon reduction that favours the reduction of the molybdenum phase instead of the support and leads to the formation of paramagnetic centres upon reduction. As a consequence, the polymeric species may be active in oxidation reactions, whereas monomeric species are not. In order to strengthen the conclusions, the reduction of a tetrameric species has also been investigated and shows that it can be reduced by H 2.

Comprehensive survey of Nd 3+ substitution In La 2Mo 2O 9 oxide-ion conductor

Differential thermal analysis coupled to temperature-controlled diffraction have given evidence of a topological metastability phenomenon in an extended compositional range of the La 2− x Nd x Mo 2O 9 solid solution. A metastable–stable phase diagram is proposed for this series of LAMOX-type fast oxide-ion conductors. In the Nd range 0< x⩽0.35, a freezing of the oxygen/vacancy disorder of the β-phase at ambient temperature can be achieved through a splat-quenching to water–ice mixture or/and shaping/sintering into pellet. In the intermediate 0.4⩽ x⩽1.2 range, the amount of β-metastable phase grows upon substitution for powders. The negative impact of β-metastable to α phase transition on conductivity tends to disappear through the partial stabilization of the β phase by shaping/sintering.