Coordination number of molybdenum(VI) in monomeric molybdic acid

Cruywagen, J. J.; Rohwer, E.F.C.H.

doi:10.1021/ic50154a061

Cited by 78 publications

(61 citation statements)

References 2 publications

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“…, respectively. The subsequent addition of niobium oxalate (in amount that corresponds to the atomic ratio Nb/Mo = 0.27/1) is accompanied with the formation of a sediment and with a decrease in pH to 3.5, which corresponds to the region of existence of octamolybdate Mo 8 O 26 4-in aqueous molybdate solutions [7]. At that, the 95 М о spectra (Fig.…”

Section: Resultsmentioning

confidence: 95%

The formation of an active component in V-Mo-Nb-O catalysts of ethane oxidation and ammoxidation

Бондарева

Андрушкевич

Aleshina

et al. 2006

React Kinet Catal Lett

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Genesis of an active component in V-Mo-Nb-O catalysts for the oxidation and ammoxidation of ethane was studied. It was shown that the mixing of aqueous solutions of initial reactants leads to the formation of MoV complexes in the solution and to sedimentation of a binary Nb-Mo compound. The latter serves as the basis for the formation of the catalyst active component phase (a triple V-Mo-Nb compound with a variable composition of Mo 5 O 14 -like structure) during the subsequent treatment in air at 400°C.

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Section: Resultsmentioning

confidence: 95%

The formation of an active component in V-Mo-Nb-O catalysts of ethane oxidation and ammoxidation

Бондарева

Андрушкевич

Aleshina

et al. 2006

React Kinet Catal Lett

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“…It has been confirmed 10,18 that the tetrahedral ion MoO4 2-transforms into an octahedral especies at the stage of second protonation. When a basic molybdate solution at millimolar or higher concentrations is acidified, the molybdate ions have been found to condense in definite steps, as evidenced by the foregoing electrometric study, to form different isopolymolybdate species.…”

Section: Isopolymolybdate Anionsmentioning

confidence: 84%

Electrometric investigations on the system acid-molybdate and the formation of heavy metal molybdates

Prasad¹,

Guimarães²

1998

J. Braz. Chem. Soc.

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A natureza precisa dos poliânions formados pela ação de ácido clorídrico sobre soluções de molibdato de sódio foi estudada por meio de titulações de pH e condutométricas. As inflexões e degraus nas curvas de titulações indicaram a formação de ânions polimolibdatos para-Mo7O24 6-e octa-Mo8O26 4-ao redor do pH 5,5 e 4,1, correspondendo às razões 8H:7Mo e 3H:2Mo, respectivamente. Titulações semelhantes de pH e condutométricas entre Hg 2+ e MoO4 2-, Mo7O24 6-e Mo8O26 4-forneceram evidências incontestáveis sobre a formação de molibdato normal HgO.MoO3, paramolibdato 3HgO.7MoO3 e octamolibdato 2HgO.8MoO3 de mercúrio(II) nas vizinhanças de pH 4,9; 4,2 e 3,7 respectivamente. Estudos analíticos também foram realizados sobre precipitados de molibdatos de mercúrio(II) confirmando os resultados obtidos pelas técnicas eletrométricas.The precise nature of the polyanions formed by the action of hydrochloric acid on sodium molybdate solutions has been studied by pH and conductometric measurements involving glass electrode and conductometric titrations. The inflections and breaks in the titration curves indicate the formation of para-Mo7O24 6-and octa-Mo8O26 4-polymolybdate anions around pH 5.5 and 4.1, corresponding to the molar ratio 8H:7Mo and 3H:2Mo, respectively. Similar pH and conductometric titrations between Hg 2 + and MoO4 2-, Mo7O24 6-, and Mo8O26 4-provide definite evidence for the formation of normal molybdate HgO.MoO3, paramolybdate 3HgO.7MoO3 and octamolybdate 2HgO.8MoO3 of mercury(II) in the vicinity of the pH 4.9, 4.2 and 3.7, respectively. The analytical investigations of the precipitates of mercuric molybdates have also been carried out, which substantiate the results of the electrometric study.

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“…To keep the charge electrons as far away as possible from each other because of the Coulombic repulsion [22, 35, 36a, [87][88][89], the ionic charge of the polyanion resides preferably on the surface oxygen atoms; that is, the corresponding resonance formulae are more favorable [22, 35, 36a].…”

Section: The Coulombic Repulsion Between Like Chargesmentioning

confidence: 99%

A bond model for polyoxometalate ions composed of MO6 octahedra (MOk polyhedra with k>4)

Tytko¹

Structure and Bonding

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The literature relating to the bonding in polyoxometalate ions is reviewed. The author's opinions are presented and expanded to give a bond model for polyoxometalate ions of the early transition elements (groups V and VI) composed of MO 6 octahedra (MOk polyhedra with k > 4). This bond model concerns in particular the bond valence (bond lengths) and charge distribution in the polyoxometalate ions and the factors modifying them. It is based on the following commonly used concepts and principles as applied to polyoxometalate ions: -Lewis's octet rule, extended to the decet and dodecet rule for M v and MVI; -prc-drc M----O double bond and the coordinate bond (dative bond); -the resonance concept; -the resonance bond number (or the bond valence concept and the valence sum rule); -polydentate ligands and the chelate effect; -the larger space requirements of unshared electron pairs (cf. the VSEPR model); -the model of multicenter prc-drc multiple bonds for certain #-oxo bridges between metal atoms; -Bronsted's acid/base concept and acid/base equilibria; -Pauling's rules for the acid/base strength of (monomeric) oxoacids/oxoanions; -the law of mass action (Le Chatelier's principle), and others. The result is a set of resonance structures for polyoxometalate species in which three types of resonance can be distinguished. These, in turn, explain: -the cohesion of the strongly distorted tetrahedral M04 building units in the structures by formation of MO 6 octahedra and hence the enhanced stability of the polyoxometalate ions; -the distribution of the formal ionic charge over (nearly) all types of oxygen atoms, but preferably the terminal ones; -the occurrence of positively charged oxygen atoms, caused by charge separation processes; -the enhanced basicity of polyoxometalate ions; and further features. A "meshing effect" defines the increase of the bond valence in inner (bridging) M-O bonds and hence the stabilization of the structures due to extension of the coordination spheres of MO4 tetrahedra. Thus, the bond lengths of the different structure types are governed by a maximization of the bond valence of the inner, bridging (or minimization of the bond valence of the outer, terminal, in contrast to frequent statements in the literature) M-O bonds. The limits of the maximization of the inner bond valences of the polyoxometalate ions are determined -by minimum stoichiometric requirements for corresponding resonance formulae (inevitability of charge on bridging oxygen atoms); -by the necessity to fulfill simultaneously the geometrical relationships of the M-O bond lengths (as defined by their interdependence in the M-O frameworks) and the valence

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Coordination number of molybdenum(VI) in monomeric molybdic acid

Cited by 78 publications

References 2 publications

The formation of an active component in V-Mo-Nb-O catalysts of ethane oxidation and ammoxidation

The formation of an active component in V-Mo-Nb-O catalysts of ethane oxidation and ammoxidation

Electrometric investigations on the system acid-molybdate and the formation of heavy metal molybdates

A bond model for polyoxometalate ions composed of MO6 octahedra (MOk polyhedra with k>4)

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