Multicomponent polyanions. 39. Speciation in the aqueous hydrogen ion-molybdate(MoO42-)-hydrogenphosphate(HPO42-) system as deduced from a combined Emf-phosphorus-31 NMR study

Pettersson, Lage; Andersson, Ida; Oehman, L.-O.

doi:10.1021/ic00246a028

Cited by 156 publications

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“…The 31 P NMR spectrum of a 5 0 10 !3 M solution of I in acetonitrile contains a single signal with d P 35.20 ppm, which is consistent with the data of [8] for b-[PMo 12 O 40 ] 3! .…”

supporting

confidence: 89%

“…Furthermore, in the presence of the above-mentioned solvents, depending on the concentration of the complexes with respect to P(V), formation of [P 2 Mo 18 O 64 ] 6! anions (d P 32.40 ppm) is possible [8].…”

mentioning

confidence: 98%

“…However, the increased molar extinction coefficient, which served as criterion of the a 6 b isomerization, could also be due to a higher actual content of the a isomer in the presence of aprotic organic solvents because of a lower degree of its hydrolytic dissociation to [PMo 11 O 39 ] 7! [8]. Furthermore, in the presence of the above-mentioned solvents, depending on the concentration of the complexes with respect to P(V), formation of [P 2 Mo 18 O 64 ] 6!…”

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confidence: 99%

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One-Step Synthesis of Tetraalkylammonium Salts of the β Isomer of 12-Molybdophosphate

Trokhimenko¹

2005

Russ J Gen Chem

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One of the properties of heteropoly complexes with the central P, Si, As, and Ge atoms and peripheral Mo, W, and V atoms is the capability to exist in the form of geometric isomers [1]. The geometric isomerism is characteristic, in particular, of heteropoly complexes with the tetrahedral surrounding of the central atom, i.e., for Keggin and Dawson structures. The coordination sphere of such complexes consists of M 3 O 13 triads each of which is built of three distorted tetrahedra sharing common edges. In the Keggin structure of 12-molybdophosphate a-PMo 12 O 4 3 0 ! , four Mo 3 O 13 triads share common vertices with each other and with the central PO 4 tetrahedron [2].The Keggin structure may exist in the form of five geometric isomers. A turn of one, two, three, or all the four Mo 3 O 13 triads by 60o around the C 3 axis of the symmetrical a isomer, according to a theoretical analysis [3], gives rise to b, g, g`, and g``forms, respectively. In the g forms, in contrast to the a and b forms, the triads share common edges rather than vertices, which results in shorter Mo3Mo distances and stronger electrostatic repulsion. Such anions are thermodynamically unstable. Indeed, only a and b isomers were obtained in solution and isolated in the solid state. The structure of the a isomers is more favorable energetically than that of the b isomers; therefore, b isomers, as a rule, irreversibly isomerize into a isomers in aqueous solutions [4]. Reduction of heteropoly complexes, on the contrary, is accompanied by the a 6 b isomerization [5]. The published procedure [6] for preparing the tetrabutylammonium salt of the b isomer of 12-molybdophosphate, b-[(n-C 4 H 9 ) 4 N] 3 . [PMo 12 O 40 ] (I), involves reoxidation of the reduced four-electron acid b-H 7 PMo 12 O 40 . The synthesis is performed in three steps: (a) preparation of a Mo(V) solution by acidification and electrolytic reduction of a Na 2 MoO 4 solution, (b) synthesis of b-[PMo 12 O 40 ] 7! in aqueous solutions from H 3 PO 4 , Mo(V), and Na 2 MoO 4 , and (c) reoxidation of b-H 7 PMo 12 O 40 and isolation of solid compound I with tetrabutylammonium bromide. Hori and Fujinaga [7] reported on formation of b-[PMo 12 O 40 ] 3! in aqueous-organic solutions from a-[PMo 12 O 40 ] 3! under the action of acetone or other aprotic solvents. The formation of the b isomer was judged from the spectrophotometric data only. However, the increased molar extinction coefficient, which served as criterion of the a 6 b isomerization, could also be due to a higher actual content of the a isomer in the presence of aprotic organic solvents because of a lower degree of its hydrolytic dissociation to [PMo 11 O 39 ] 7! [8]. Furthermore, in the presence of the above-mentioned solvents, depending on the concentration of the complexes with respect to P(V), formation of [P 2 Mo 18 O 64 ] 6! anions (d P 32.40 ppm) is possible [8].We found by 31 P NMR that additions of lowmolecular-weight monobasic carboxylic acids (formic, acetic, propionic) suppress the dissociation of 12-molybdophosphate (33.20 p...

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“…The 31 P NMR spectrum of a 5 0 10 !3 M solution of I in acetonitrile contains a single signal with d P 35.20 ppm, which is consistent with the data of [8] for b-[PMo 12 O 40 ] 3! .…”

supporting

confidence: 89%

mentioning

confidence: 98%

mentioning

confidence: 99%

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One-Step Synthesis of Tetraalkylammonium Salts of the β Isomer of 12-Molybdophosphate

Trokhimenko¹

2005

Russ J Gen Chem

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“…Upon calcination these entities are transformed into the aforementioned tetrahedral adsorbed entities and upon transfer in the wet atmosphere the AlMo 6 entities are restored as shown by Raman spectra in Fig 7d and ) [28], the structure of which being given in figure 2d. The formation of this HPA was also evidenced by P NMR spectroscopy by a line at -2.45 ppm as shown in figure 9 [28].…”

Section: Iii2a Ammonium Heptamolybdate Based Impregnating Solutionsmentioning

confidence: 94%

New insight in the preparation of alumina supported hydrotreatment oxidic precursors: A molecular approach

Blanchard

Lamonier

Griboval-Constant

et al. 2007

Applied Catalysis A: General

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The science on the preparation of the hydrodesulfurization oxidic precursors is coming of age, but the chemistry governing their preparation is not yet clearly understood. In this paper, the chemistry of alumina supported oxomolybdate preparation is revisited taking into account the dissolution/precipitation concept recently developed. Classical preparations with the ammonium heptamolybdate and Co nitrate salts will firstly be discussed. Then the use of new starting materials for the preparation of the impregnating solutions will be considered, showing that at high Mo loading the dispersion is strongly dependant on the nature of the starting salts. The use of phosphomolybdate cobalt salts will also be considered. Lastly we will discuss the improvement of the Co promoting effect using molybdocobaltate heteropolyanions as starting materials and complexing agents. This study shows that the maturation step is the determining step for the improvement of preparation of these alumina based oxidic precursor.

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“…Some molybdate analogues have been isolated 160 or otherwise identified in equilibrium studies. 19,161,162 All these lacunary anions have structures in which no MO 6 octahedron has more than two (cis) terminal oxygens, and are convenient synthetic precursors of substituted "plenary" anions and functionalized species. The monovacant anions (entries 1-4, 9-11 in Table 12) generate a vast number of species in which the substituent atom is a metal cation bearing a variety of terminal ligands, or in some cases none (e.g., Sn 2þ , 163 Co 2þ , 164 ).…”

Section: Lacunary Forms Of Keggin and Wells-dawson Anionsmentioning

confidence: 99%

Polyoxo Anions: Synthesis and Structure

Pope

2013

Reference Module in Chemistry, Molecular Sciences and Chemical Engineering

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Multicomponent polyanions. 39. Speciation in the aqueous hydrogen ion-molybdate(MoO42-)-hydrogenphosphate(HPO42-) system as deduced from a combined Emf-phosphorus-31 NMR study

Cited by 156 publications

References 0 publications

One-Step Synthesis of Tetraalkylammonium Salts of the β Isomer of 12-Molybdophosphate

One-Step Synthesis of Tetraalkylammonium Salts of the β Isomer of 12-Molybdophosphate

New insight in the preparation of alumina supported hydrotreatment oxidic precursors: A molecular approach

Polyoxo Anions: Synthesis and Structure

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