The crystal structure of pascoite, Ca3V10O28.16H2O

Swallow, A. G.; Ahmed, Faruk; Barnes, W. H.

doi:10.1107/s0365110x66002974

Cited by 71 publications

(26 citation statements)

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“…From the sum of the bond valences ("bond strengths") 1 about the oxygen atoms in several isopolyoxometalate ions [8][9][10][11][12][13], the present author [14a, 15a] concluded, contrary to the above proposal, that the ionic charge is mainly distributed over the terminal oxygen atoms which, therefore, are the most basic oxygen atoms of a polyoxometalate structure. This is in line with -the observation that the cations in polyoxometalates are in contact mainly with the terminal oxygen atoms of the polyanions [8][9][10][11][12][13][16][17][18][19], -the assumption that in ion pairs (i.e., in solution) the cations are in contact with terminal oxygen atoms of the polyanions [10,11,20], and -the view that terminal oxygen atoms behave as if they are bigger than the other oxygen atoms [21] or make available more space to the unshared electron pairs in which the charge electrons are merged in [14a, 22a].…”

Section: Introductionsupporting

confidence: 68%

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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Section: Introductionsupporting

confidence: 68%

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

Tytko¹

Structure and Bonding

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“…The study of hummerite led us to re-examine the atomic arrangement of pascoite. That arrangement was not well defined, as the only previous structural study (Swallow et al 1966) did not reveal hydrogen atom positions nor did it offer a definitive space-group. Candidate space-groups I2 and I2/m both yielded realistic structure-models, with nearly identical R values, that correspond to ordered and disordered models, respectively.…”

Section: (Traduit Par La Rédaction)mentioning

confidence: 83%

“…Bond-valence calculations allow all three possibilities for Ca1 coordination (Table 3); the half-occupied nature of the O13X sites yields the average coordination of Ca1O 7 . The possibility of such disorder was recognized by Swallow et al (1966).…”

Section: The Interstitial Complexmentioning

confidence: 97%

“…The initial solution was undertaken without knowledge of the earlier solution proffered by Swallow et al (1966). Their solution was undertaken in the nonconventional space-groups I2 and I2/m; those authors tentatively concluded that the ordered I2 model was correct, although they noted that their conclusion that the mineral crystallized in the acentric alternative was not definitive.…”

Section: (Traduit Par La Rédaction)mentioning

confidence: 99%

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THE C2/m DISORDERED STRUCTURE OF PASCOITE, Ca3[V10O28]{middle dot}17H2O: BONDING BETWEEN STRUCTURAL UNITS AND INTERSTITIAL COMPLEXES IN COMPOUNDS CONTAINING THE [V10O28]6 DECAVANADATE POLYANION

Hughes¹,

Schindler²,

Francis³

2005

The Canadian Mineralogist

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The atomic arrangement of pascoite has been solved and refined to R = 0.0257 using three-dimensional data obtained with MoKa X-radiation and a CCD detector. The mineral crystallizes in space group C2/m, a 19.5859(6), b 10.1405(3), c 10.9110(3) Å, b 120.815(1)°. The atomic arrangement of pascoite was previously presented in two possible space-groups, consistent with a C2/m disordered model and a C2 ordered model. The earlier authors preferred the ordered model, but noted the ambiguity of the solution. Using CCD data and locating the hydrogen atoms allow us to assign the C2/m disordered model to the atomic arrangement. The structural unit, or anionic portion of the atomic arrangement in pascoite, is the decavanadate polyanion (V 10 O 28 ) 6-, similar to the decavanadate group found in hummerite and numerous synthetic vanadates. Linking the decavanadate groups together are interstitial groups, formed of the cationic group {Ca 3 (H 2 O) 17 } 6+ . All oxygen atoms in the interstitial complex occur as (H 2 O) groups, in contrast to the structural unit, which is devoid of hydrogen atoms. There are two distinct Ca atoms in the interstitial complex. The disorder that occurs in the coordinating oxygen atoms leads to an average coordination of Ca1O 7 for the Ca1 atom, although the disordered coordinating oxygen atoms yield possible Ca1O 6 , Ca1O 7 , and Ca1O 8 coordinations. The Ca2 atom, in Ca2O 7 coordination, also bonds to disordered oxygen atoms. Examination of the structure of compounds with the decavanadate polyanion structural unit and with simple mono-, di-, and trivalent cations in the interstitial complex demonstrates that the sum of bonds emanating from the interstitial cations correlates with the number of (H 2 O) groups per cation. SoMMaiRENous avons déterminé l'agencement des atomes dans la pascoïte, et nous l'avons affiné jusqu'à un résidu R égal à 0.0257 en utilisant des données tridimensionnelles obtenues avec rayonnement MoKa et un détecteur de type CCD. Ce minéral cristallise dans le groupe spatial C2/m, a 19.5859(6), b 10.1405(3), c 10.9110(3) Å, b 120.815(1)°. L'agencement des atomes de la pascoïte était antérieurement présenté en deux groupes d'espace possibles, un modèle désordonné conforme au groupe C2/m et un modèle ordonné C2. Les auteurs antérieurs ont préféré le modèle ordonné, mais ont souligné l'ambiguïté de la solution. Avec des données CCD et la possibilité de bien situer les atomes d'hydrogène, nous avons pu conclure que le modèle désordonné C2/m est le bon. L'unité structurale, c'est-à-dire la portion anionique de la structure, est le polyanion décavanadate (V 10 O 28 ) 6-, que l'on retrouve dans la hummerite et de nombreux vanadates synthétiques. Ce sont les groupes interstitiels qui joignent les groupes décavanadate; ils contiennent le groupe cationique {Ca 3 (H 2 O) 17 } 6+ . Tous les atomes d'oxygène du complexe interstitiel font partie de groupes (H 2 O), contrairement à l'unité structurale, qui est dépourvue d'atomes d'hydrogène. Il y a deux atomes de Ca dans le complexe interstitiel....

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“…The structural similarity of decavanadate (V1002S6-) [21,22] with IP3 suggested that they might interact with the same sites. Therefore, we investigated the effects of different vanadate species on binding of IP3 to its receptor.…”

Section: Decavanadate Displaces Ip3from Its Receptormentioning

confidence: 99%

Decavanadate displaces inositol 1,4,5-trisphosphate (IP3) from its receptor and inhibits IP3 induced Ca2+ release in permeabilized pancreatic acinar cells

et al. 1991

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-Inositol 1,4,5-trisphosphate (IP3) induced Ca 2 + release in digitonin permeabllized rat pancreatic acinar cells is specifically inhibited by decavanadate. The ca 2 + release induced with 0.18 flM IP3 is half maximally inhibited with approximately 5 flM decavanadate. Complete inhibition is achieved with around 20 flM decavanadate. Removal of decavanadate from the permeabilized cells fully restores sensitivity towards IP3, indicating the reversibility of the inhibition. Oligovanadate, which inhibits A TP dependent ca 2 + up1ake into intracellular stores, does not influence IP3 induced ca 2 + release. In order to reveal the mechanism underlying the effects of the different vanadate species, binding of IP3 to the same cellular preparations was investigated. We found that binding of IP3 to a high affinity receptor site (I

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The crystal structure of pascoite, Ca₃V₁₀O₂₈.16H₂O

Cited by 71 publications

References 1 publication

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

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

THE C2/m DISORDERED STRUCTURE OF PASCOITE, Ca3[V10O28]{middle dot}17H2O: BONDING BETWEEN STRUCTURAL UNITS AND INTERSTITIAL COMPLEXES IN COMPOUNDS CONTAINING THE [V10O28]6 DECAVANADATE POLYANION

Decavanadate displaces inositol 1,4,5-trisphosphate (IP3) from its receptor and inhibits IP3 induced Ca2+ release in permeabilized pancreatic acinar cells

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