Polymolybdates

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. 

Polymerisierbarkeit, /. polymerizability, polymerisieren, v.t. i. polymerize, Polymerisierung, /. polymerization. Polymolybdansaure, /. polymolybdic acid, polymorph, polymorphisch, a. polymorphous, polymorphic. 

Even more remarkable differences arise after calcination at 775 K. The sharp Raman spectra of the calcined Mo03/Si02 catalysts are those of crystalline Mo03. No crystalline Mo03 is present in the calcined Mo03/Al203 catalysts, however. Here the Raman spectra show similarities with those of the polymolybdates, which indicates that these species have a sufficiently strong interaction with the alumina support to withstand calcination at 775 K. 

Specifics such as indications that Bronsted acidity may be associated with polymolybdate structure and the observation of a low frequency feature at 1310 reciprocal centimeters will be described along with generalizations regarding the present limitations of this technique. 

Counter ions play a decisive role in the isolation of polyoxoanions. Ions occurring in negligible amounts in solution such as [Mo6Oi9]2 can be precipitated from aqueous solution with the cation [(C4H9)4N]+ while major species remain in solution. Different ions can be isolated at the same pH by using different cations. Conditions favorable for the precipitation of some polymolybdates from aqueous solution with the cations NH4, [(NH2)3C]+, [(CH3)4N]+, and [(n-C4H9)4N)]+ have been determined (98). The polyions isolated with these and some other cations are listed in Table VII. Most of these polyions have been structurally characterized. 

A mixed-valent polymolybdate on active carbon was prepared from molybdenum metal and H202, followed by the addition of active carbon to the aqueous solution [114,115], This catalyzed the epoxidation of several alkenes in 2-propanol using H202 as an oxidant, while the efficiency of H202 utilization was very low (< 25%). The epoxidation likely proceeded mainly on the surface of the catalyst because the recovered catalyst showed almost similar catalytic activity. 

Srinivasan and Ford [158] reported that epoxidation of cyclooctene using excess H202 was catalyzed by polymolybdate such as [Mo7024]6 tethered on the colloidal polymer with alkylammo-nium cations. Cyclooctene was oxidized to give 1,2-epoxy cyclooctane with >99% selectivity at 90% conversion for 24 h at 313 k ... 

Aveston J, Anacker EW, Johnson JS (1964) Hydrolysis of molybdenum (VI). Ultracentrifugation, acidity measurements, and Raman spectra of polymolybdates. Inorg Chem 3 735-746 Baes Jr. CF, Mesmer RE (1986) The Hydrolysis of Cations. Krieger Publishing Company, Melbourne, EL Barling J, Anbar AD (2004) Molybdenum isotope fractionation during adsorption by manganese oxides. Earth Planet Sci Lett, in press... 

SiMouO ]4-.134 The structure of the heteropoly blue species (four-electron-reduced PM012O40]3-) formed in the molybdenum blue determination of phosphorus has been reported135 and a review of molybdate heteropoly blues has appeared.130 A stability index of polyanion structures has been discussed.137 The presence of two PMo, anions in aqueous solutions of molybdate and phosphate has been demonstrated by 31P NMR.138 Solid state NMR (nonspinning and MAS techniques) has been used for characterization of heteropolyanions.139 Molybdenum-95 NMR spectra of some polymolybdates have been reported.140... 

Solutions of MoVI acidified to H+/[Mo04]2 1.8 contain one or more very large polymolybdate structures. Earlier measurements based on ultracentrifugation and EMF... 

Mononuclear examples are dominant in the simple coordination chemistry of molybdenum(VI). This is due in part to the absence of d electrons in Movl complexes, which precludes the formation of MoVI—Mo 1 metal-metal bonds. However, note must be taken of the very large class of homo- and hetero-polymolybdates which contain polynuclear Mo. These... 

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