Anions molybdate

Figure B 1.11.5 is an example of how relative integrals can detennine structure even if the peak positions are not adequately understood. The decavanadate anion has the structure shown, where oxygens lie at each vertex and vanadiums at the centre of each octaliedron. An aqueous solution of decavanadate was mixed with about 8 mol% of molybdate, and the tiiree peaks from the remaining decavanadate were then computer-subtracted...

Molybdate orange and red are pigments (qv) that contain lead(II) molybdate [10190-33-3], PbMoO, formulated in mixed phases with PbCrO and PbSO. The mixed phase is more intensely colored than any of the component phases. Concerns about lead content are lessening the use of these materials (see also Paint). Various organic dyes are precipitated with heteropolymolybdates. This process allows the fixation of the dye in various fabrics. The molybdenum anion generally imparts light stabiHty to the colorant as weU (91). 

Soil Nutrient. Molybdenum has been widely used to increase crop productivity in many soils woddwide (see Fertilizers). It is the heaviest element needed for plant productivity and stimulates both nitrogen fixation and nitrate reduction (51,52). The effects are particularly significant in leguminous crops, where symbiotic bacteria responsible for nitrogen fixation provide the principal nitrogen input to the plant. Molybdenum deficiency is usually more prominent in acidic soils, where Mo(VI) is less soluble and more easily reduced to insoluble, and hence unavailable, forms. Above pH 7, the soluble anionic, and hence available, molybdate ion is the principal species. 

Sensitivity of the proposed method correlates with molai absorptivity of the cyanine dye. Mixed POMs PMeMo O j (Me=TP+, Sb +, BP+) were chosen as analytical form because of its higher stability as compared with 12-molybdophosphate. Only 2-3T0 concentration of molybdate is enough for complete formation of POM avoiding in this way formation of lA with polymolybdate ions. In addition, mixed POMs are stable in wider interval of pH. Increasing of anion chai ge from 3 to 5(6) is also favorable. Constant absorbance of lA is observed in the acidity range of 0.12-0.28 M. 

Mild and reversible reduction of 1 12 and 2 18 heteropoly-molybdates and -tungstates produces characteristic and very intense blue colours ( heteropoly blues ) which find application in the quantitative determinations of Si, Ge, P and As, and commercially as dyes and pigments. The reductions are most commonly of 2 electron equivalents but may be of 1 and up to 6 electron equivalents. Many of the reduced anions can be isolated as solid salts in which the unreduced structure remains essentially unchanged and... 

Fluoride, in the absence of interfering anions (including phosphate, molybdate, citrate, and tartrate) and interfering cations (including cadmium, tin, strontium, iron, and particularly zirconium, cobalt, lead, nickel, zinc, copper, and aluminium), may be determined with thorium chloranilate in aqueous 2-methoxyethanol at pH 4.5 the absorbance is measured at 540 nm or, for small concentrations 0-2.0 mg L 1 at 330 nm. 

Molybdate is always used in conjunction with other anion inhibitors, not only to reduce the cost of the inhibitor program, but also because, through synergism, much-improved barrier films are produced when coupled with nitrite or silicate. 

Selective oxidation and ammoxldatlon of propylene over bismuth molybdate catalysts occur by a redox mechanism whereby lattice oxygen (or Isoelectronlc NH) Is Inserted Into an allyllc Intermediate, formed via or-H abstraction from the olefin. The resulting anion vacancies are eventually filled by lattice oxygen which originates from gaseous oxygen dlssoclatlvely chemisorbed at surface sites which are spatially and structurally distinct from the sites of olefin oxidation. Mechanistic details about the... 

Figure 10 Capillary ion analysis of 30 anions 1 = thiosulfate, 2 = bromide, 3 = chloride, 4 = sulfate, 5 = nitrite, 6 = nitrate, 7 = molybdate, 8 = azide, 9 = tungstate, 10 = monofluorophosphate, 11 = chlorate, 12 = citrate, 13 = fluoride, 14 = formate, 15 = phosphate, 16 = phosphite, 17 = chlorite, 18 = galactarate, 19 = carbonate, 20 = acetate, 21 = ethanesulphonate, 22 = propionate, 23 = propanesulphonate, 24 = butyrate, 25 = butanesulphonate, 26 = valerate, 27 = benzoate, 28 = D-glutamate, 29 = pentane-sulphonate and 30 = D-gluconate. Experimental conditions fused silica capillary, 60 cm (Ld 52 cm) x 50 p i.d., voltage 30 kV, indirect UV detection at 254 nm, 5 mM chromate, 0.5 mM NICE-Pak OFM Anion-BT, adjusted to pH 8.0, with 100 mM NaOH. (From Jones, W. R. and Jandik, R, /. Chromatogr., 546, 445,1991. With permission.)...

Recent data provided by Cocke et a/.174,175 in an RBS study of the distribution of heavy anions (tungstates, molybdates, manganates) yield unusual oscillatory anion profiles. 

The rate of y -alumina island formation essentially depends on the nature of the electrolyte used. If outwards migrating (in the terms of Xu et al.102) anions, such as tungstates and molybdates, are used in the anodization process, y- alumina seed crystals are surrounded by pure alumina and crystallization occurs easily. In the case of inwards migrating anions (e.g., citrates, phosphates, tartrates), the oxide material surrounding the y-nuclei is enriched... 

The effect of other inorganic anions (sulfate, molybdate, silicate), low molecular mass organic ligands (LMMOLs, such as oxalate, malate, citrate, tartrate and succinate), and fulvic or humic acid on the sorption of arsenate and arsenite onto variable charge minerals and soils has been studied (Roy et al. 1986 Grafe et al. 2001 Liu et al. 2001 Violante et al. 2005a,b). 

Isaeva [181] described a phosphomolybdate method for the determination of phosphate in turbid seawater. Molybdenum titration methods are subject to extensive interferences and are not considered to be reliable when compared with more recently developed methods based on solvent extraction [182-187], such as solvent-extraction spectrophotometric determination of phosphate using molybdate and malachite green [188]. In this method the ion pair formed between malachite green and phosphomolybdate is extracted from the seawater sample with an organic solvent. This extraction achieves a useful 20-fold increase in the concentration of the phosphate in the extract. The detection limit is about 0.1 ig/l, standard deviation 0.05 ng-1 (4.3 xg/l in tap water), and relative standard deviation 1.1%. Most cations and anions found in non-saline waters do not interfere, but arsenic (V) causes large positive errors. 

Many important soil components are not present as simple cations or anions but as oxyanions that include both important metals and nonmetals. The most common and important metal oxyanion is molybdate (Mo042 ). The most common and important nonmetal oxyanions are those of carbon (e.g., bicarbonate [HC03 ] and carbonate [C032-]), nitrogen (e.g., nitrate [N03 ] and nitrite [NQ2 ]), and phosphorus (e.g., monobasic phosphate [H2P04 ], dibasic... 

Finally, mixtures of ionic salts may form glasses, which contain discrete anions (iodide, or molybdate...) without any macromolecular anions. This is the case for glasses in the Agl-AgMoO system for which the pure limiting compositions Agl or AgMoO do not form glasses. 

The chromatographic separation of technetium from molybdenum is based on the different extent to which molybdate and pertechnetate are adsorbed from alkaline and acid solutions. The distribution coefficient of molybdate between the anion exchanger Dowex 1-X8 and 3 M NaOH is 12, while it is 10 for pertechnetate under the same conditions. Molybdate is also adsorbed to a much lesser extent from hydrochloric acid solutions than pertechnetate. Thus, molybdemun can be eluted by hydroxide or HCl solutions while nitric acid, perchlorate or thiocyanate are used for the elution of technetium . 

Hall and Hohns have found that 10 /ig of technetiiun can be separated quantitatively from as much as 50 g of molybdenum using the Amberlite IRA-400 anion exchange resin in the perchlorate form. The irradiated metal is dissolved in a NaOH/HjOj mixture and the solution passed through the column. Molybdate is removed by elution with 10% NaOH solution pertechnetate is eluted with 0.5 M NH4SCN. 

Oxyanions also affect the coordination chemistry of the metal center (84). Molybdate and tungstate are tightly bound noncompetitive inhibitors (Ki s of ca. 4 (iM) (85). These anions bind to the reduced form of the enzyme, changing the rhombic EPR spectrum of the native enzyme to axial (Figure 1) and affecting the NMR shifts observed (84,85). Comparisons of the ENDOR spectra of reduced uterofenin and its molybdate complex show that molybdate binding causes the loss of iH features which are also lost when the reduced enzyme is placed in deuterated solvent (86). These observations suggest that molybdate displaces a bound water upon complexation. 

The heavy alkali molybdates and -tungstates are known to exist in an orthorhombic modification as well, having the space group D h, Z =4) (55). The IR and Raman data 84), reproduced in Table 9, show clearly that vi and vz appear in the spectra for all these substances and that vz and vi are spht into three bands in the Raman effect. These comply for the most part with the simple site symmetry treatment where the anion has Cs S5nnmetry. 

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