Synthesis and properties of pyrazine-pillared Ag3Mo2O4F7 and AgReO4 layered phases

The new pyrazine-pillared solids, AgReO₄(C₄H₄N₂) (I) and Ag₃Mo₂O₄F₇(C₄H₄N₂)₃ (C₄H₄N₂=pyrazine, pyz) (II), were synthesized by hydrothermal methods at 150 °C and characterized using single crystal X-ray diffraction (I—P2₁/c, No. 14, Z=4, a=7.2238(6) Å, b=7.4940(7) Å, c=15.451(1) Å, β=92.296(4)°; II—P2/n, No. 13, Z=2, a=7.6465(9) Å, b=7.1888(5) Å, c=19.142(2) Å, β=100.284(8)°), thermogravimetric analysis, UV-Vis diffuse reflectance, and photoluminescence measurements. Individual Ag(pyz) chains in I are bonded to three perrhenate ReO₄^- 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 Mo₂O₄F₇^3- 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 AgReO₄ for I, and Ag₂MoO₄ 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.     

Use of molybdate as novel complex-forming selector in the analysis of polyhydric phenols by capillary zone electrophoresis

Molybdate was examined as a complex-forming additive to the CE background electrolytes (BGE) to affect the selectivity of separation of polyhydric phenols such as flavonoids (apigenin, hyperoside, luteolin, quercetin and rutin) and hydroxyphenylcarboxylic acids (ferulic, caffeic, p-coumaric and chlorogenic acid). Effects of the buffer concentrations and pH and the influence of molybdate concentration on the migration times of the analytes were investigated. In contrast to borate (which is a buffering and complex-forming agent generally used in CE at pH ≥9) molybdate forms more stable complexes with aromatic o-dihydroxy compounds and hence the complex-formation effect is observed at considerably lower pH. Model mixtures of cinnamic acid, ferulic acid, caffeic acid and 3-hydroxycinnamic acid were separated with 25 mM morpholinoethanesulfonic acid of pH 5.4 (adjusted with Tris) containing 0.15 mM sodium molybdate as the BGE (25 kV, silica capillary effective length 45 cm × 0.1 mm I.D., UV-vis detection at 280 nm). With 25 mM 2-hydroxy-3-[4-(2-hydroxyethyl)-1-piperazinyl]propanesulphonic acid/Tris of pH^* 7.4 containing 2 mM sodium molybdate in aqueous 25% (v/v) methanol as the BGE mixtures of all the above mentioned flavonoids, p-coumaric acid and chlorogenic acid could be separated (the same capillary as above, UV-vis detection at 263 nm). The calibration curves (analyte peak area versus concentration) were rectilinear (r > 0.998) for ≈8-35 μg/ml of an analyte (with 1-nitroso-2-naphthol as internal standard). The limit of quantification values ranged between 1.1 mg l⁻¹ for p-coumaric acid and 2.8 mg l⁻¹ for quercetin. The CE method was employed for the assay of flavonoids in medicinal plant extracts. The R.S.D. values ranged between 0.9 and 4.7% (n = 3) when determining luteolin (0.08%) and apigenin (0.92%) in dry Matricaria recutita flowers and rutin (1.03%) and hyperoside (0.82%) in dry Hypericum perforatum haulm. The recoveries were >96%.     

Phase formation, structural and microstructural characterization of novel oxynitride-perovskites synthesized by thermal ammonolysis of (Ca,Ba)MoO4 and (Ca,Ba)MoO3

Reactions of AMoO₄ and AMoO₃ (A=Ca²⁺, Ba²⁺) with ammonia were investigated at 873 K<T<1123 K with the particular intention to synthesize novel oxynitride-perovskites of the general composition AMo(O,N)₃ and to study their crystal structure. CaMo(O,N)₃ and BaMo(O,N)₃ were prepared by thermal ammonolysis of the corresponding CaMoO₃ and BaMoO₃ precursors at T=898 and 998 K, respectively. The structural parameters of the oxynitrides were obtained from Rietveld refinements of X-ray and neutron powder diffraction data. CaMo(O,N)₃ crystallizes in the GdFeO₃ distorted perovskite structure with orthorhombic space group Pbnm and a=5.5029(1) Å, b=5.5546(1) Å, c=7.8248(1) Å as determined by X-ray powder diffraction. Its O/N content refined from the neutron diffraction data corresponds to the composition CaMoO_1.7(1)N_1.3(1). BaMo(O,N)₃ crystallizes in the cubic perovskite structure with space group Pm3¯m and a=4.0657(1) Å as determined by X-ray powder diffraction. Transmission electron microscopy reveals a complex microstructure for both CaMoO₃ and CaMoO_1.7(1)N_1.3(1) represented by twin domains of different orientation.     

Kinetic spectrophotometric determination of submicromolar orthophosphate by molybdate reduction

A kinetic spectrophotometric procedure was developed for determination of submicromolar orthophosphate based on the reaction in which orthophosphate serves as a catalyst in the reduction of molybdenum, and the initial rate of molybdenum-blue formation (λ_max = 780 nm) is proportional to the concentration of orthophosphate in the samples. The detection limit (3 × standard deviation of blank, n = 8) was 6 nM and the linear calibration ranged from 10 to 100 nM (r² = 0.997). The precisions of this method were 3.3% at 10 nM and 5.4% at 50 nM (n = 8), respectively. Similar to other molybdate based methods, silica and arsenate in the samples can interfere with phosphate determination. The responses of silicate and arsenate were about 25% and 7% of that of orthophosphate, respectively, and their interferences were enhanced in the presence of phosphate in the samples due to the synergistic effect of phosphate with arsenate or silicate on the molybdate reagent.     

Influence of fluoride on f-f transitions of Eu in LiEuM2O8 (M=Mo, W)

The influence of fluoride on the luminescence of LiEuM₂O₈ (M=Mo, W) was studied. LiEuMo₂O₈ and LiEuW₂O₈ formed the whole range of solid solutions, which emitted intense red luminescence under the excitations by 395, 465 and 535 nm wavelengths. When doped with fluoride, the materials also formed solid solutions and the luminescent intensity was remarkably enhanced. The phosphor with optimized compositions in this system would be a promising red component for solid-state lighting devices based on GaN light-emitting diodes.     

Characterisation of the anodic layers formed on 2024 aluminium alloy, in tetraborate electrolyte containing molybdate ions

Anodic layer growth on 2024 aluminium alloy at 70 °C, under 40 V, during 60 min, in 50 g L⁻¹ di-sodium tetraborate solution containing di-sodium molybdate from 0.1 to 0.5 M (pH 10) is examined. Anodising behaviours strongly depend on additive concentration. Development of anodic films is favoured with weak molybdate additions (<0.3-0.4 M). The film thicknesses increase and the porosity of anodic layers decreases. Molybdenum (+VI), detected by X-ray photoelectron spectroscopy (XPS) analysis, is present in the anodic films and the Mo incorporation, studied by energy dispersive spectroscopy (EDS) analysis, increases with molybdate concentration. However, for high molybdate concentrations (>0.4 M), anodising behaviour becomes complex with the formation of a blue molybdenum oxide at the cathode. The growth of aluminium oxide is hindered. As the anodic layers are thinner, the Mo(+VI) incorporation significantly decreases. These two configurations implicate different corrosion performances in 5% sodium chloride solution at 35 °C. As the alkaline anodic layer formed with 0.3 M molybdate species is the thickest and the Mo incorporation is the more pronounced, its corrosion resistance is the highest. The effect of morphology and composition of anodic films on pitting corrosion is also discussed.     

Dimethylsulfoxide as a kinetic booster for the chemical generation of singlet oxygen in methanol

The kinetic booster effect of dimethylsulfoxide on the chemical generation of singlet oxygen, ¹O₂, from the disproportionation of hydrogen peroxide catalyzed by molybdate ions in methanol has been evidenced by detection of the IR luminescence of ¹O₂ at 1270 nm and by ⁹⁵Mo NMR spectroscopy. DMSO interacts rapidly, through a direct oxygen transfer with the stable tetraperoxomolybdate , leading to DMSO₂ and to the unstable triperoxomolybdate , which releases ¹O₂. The procedure was applied to accelerate the dark singlet oxygenation of β-citronellol and α-terpinene.     

(Me2NH2)[(Ph3Sn)3(MoO4)2], ein Triorganozinnmolybdat mit Schichtstruktur

(Me₂NH₂)[(Ph₃Sn)₃(MoO₄)₂], a Triorganotin Molybdate with Layer Structure The reaction of [(Ph₃Sn)₂MoO₄] with (Me₂NH₂)Cl in an acetonitrile/water mixture leads to the formation of (Me₂NH₂)[(Ph₃Sn)₃(MoO₄)₂] ( 1 ). ( 1 ) crystallizes in the space group Pca2₁ with a = 1967.0(4), b = 1353.1(2) and c = 2176.6(5) pm. In the crystal structure of 1 Ph₃SnO₂ bipyramides and MoO₄ tetrahedra are linked by corner sharing to give a layer structure. Additionally the layers are connected by O···H···N hydrogen bridges between MoO₄ groups and [Me₂NH₂]⁺ ions to give a 3D network structure.     

铑（Ⅲ）－钼酸盐－罗丹明B显色体系的研究和应用

在聚乙烯醇（ＰＶＡ）存在下，铑（Ⅲ）与钼酸盐和罗丹明Ｂ（ＲＢ）形成离子缔合物，缔合物的最大吸收位于５８０ｎｍ，摩尔吸光系数ε值１．６８×１０５Ｌ·ｍｏｌ－１·ｃｍ－１，服从比耳定律范围０～１０μｇＲｈ／２５ｍＬ，方法用于催化剂和冶金产品中铑的测定，结果满意     

Using sequential injection analysis for fast determination of phosphate in coastal waters

A sequential injection analysis system (SIA) is described which is suited for the fast determination of filterable molybdate reactive phosphate (FRP, 0.2 μm) in coastal waters. It processes up to 270 samples per hour with a detection limit (3σ) of 0.05 μM and is used for surface mapping of phosphate in areas with steep concentration gradients like the Wadden Sea. The determination is based on the reaction of phosphate with acidic molybdate to phosphomolybdate, which builds non-fluorescent ion pairs with rhodamine 6G. The remaining rhodamine fluorescence is detected at 550 nm with an excitation at 470 nm. Syringe pump, valve and detector were controlled by a self made python programme, which was optimised for high speed SIA measurements in monitoring applications.