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Dawson Structure
The Dawson structure is a well-known structural motif for heteropoly acids. The Dawson structure can be viewed as the fusion of two defect Keggin structure, fragments with three missing octahedra. As in Keggin structures, the Dawson structure has an oxyanion at its core. Unlike Keggin structures, there are two such anions, one at each side of the ellipsoidal anion. An example is , which can also be described as . Commonly, Dawson structures feature phosphate as the central oxyanion An oxyanion, or oxoanion, is an ion with the generic formula (where A represents a chemical element and O represents an oxygen atom). Oxyanions are formed by a large majority of the chemical elements. The formulae of simple oxyanions are determine ...s. When the Keggin anion is allowed to stand in aqueous solution, it converts to . References {{reflist Cluster chemistry Heteropoly acids Anions ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dawson Ion
Dawson may refer to: People and fictional characters *Dawson (surname), including a list of people and fictional characters with the name * Dawson (given name), including a list of people and fictional characters with the name Places Antarctica *Dawson Head, Palmer Land * Dawson Nunatak, Mac. Robertson Land * Dawson Peak, Ross Dependency Australia *Division of Dawson, an electoral district in the Australian House of Representatives, in Queensland * Dawson River (New South Wales) *Dawson River (Queensland), a river in eastern Queensland, Australia * Dawson, South Australia, a locality and former town northeast of Peterborough Canada *Dawson City, Yukon * Dawson (electoral district), Yukon Territory * Dawson Range (Yukon), in the Yukon Ranges *Dawson Creek, a city in northeastern British Columbia, Canada *Dawson Range (British Columbia) * Dawson Falls, British Columbia * Dawson, Ontario, a township *Dawson Township, Manitoulin District, Ontario United States * Dawson, Ala ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heteropoly Acid
The heteropolymetalates are a subset of the polyoxometalates, which consist of three or more transition metal oxyanions linked together by shared oxygen atoms to form a closed 3-dimensional molecular framework. In contrast to isopolymetalates, which contain only one kind of metal atom, the heteropolymetalates contain differing main group oxyanions. The metal atoms are usually group 6 element, group 6 (Mo, W) or less commonly Group 5 element, group 5 (V, Nb, Ta) transition metals in their highest oxidation states. They are usually colorless to orange, diamagnetic anions. For most heteropolymetalates the W, Mo, or V, is complemented by main group oxyanions phosphate and silicate. Many exceptions to these general statements exist, and the class of compounds includes hundreds of examples. Structure Certain structural motifs recur. The Keggin ion for example is common to both molybdates and tungstates with diverse central heteroatoms. The Keggin and Dawson structures have tetrahedral m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Keggin Structure
The Keggin structure is the best known structural form for heteropoly acids. It is the structural form of α-Keggin anions, having a general formula of , where X is the heteroatom (most commonly are pentavalent phosphorus PV, tetravalent silicon SiIV, or trivalent boron BIII), M is the addendum atom (most common are molybdenum Mo and tungsten W), and O represents oxygen. The structure self-assembles in acidic aqueous solution and is a commonly used as a type of polyoxometalate catalysts. History The first α-Keggin anion, ammonium phosphomolybdate (), was first reported by Jöns Jakob Berzelius in 1826. In 1892, Blomstrand proposed the structure of phosphomolybdic acid and other poly-acids as a chain or ring configuration. Alfred Werner, using the coordination compounds ideas of Copaux, attempted to explain the structure of silicotungstic acid. He assumed a central group, ion, enclosed by four , where R is a unipositive ion. The are linked to the central group by primary v ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phosphate
Phosphates are the naturally occurring form of the element phosphorus. In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid, phosphoric acid . The phosphate or orthophosphate ion is derived from phosphoric acid by the removal of three protons . Removal of one proton gives the dihydrogen phosphate ion while removal of two protons gives the hydrogen phosphate ion . These names are also used for salts of those anions, such as ammonium dihydrogen phosphate and trisodium phosphate. File:3-phosphoric-acid-3D-balls.png, Phosphoricacid File:2-dihydrogenphosphate-3D-balls.png, Dihydrogenphosphate File:1-hydrogenphosphate-3D-balls.png, Hydrogenphosphate File:0-phosphate-3D-balls.png, Phosphate or orthophosphate In organic chemistry, phosphate or orthophosphate is an organophosphate, an ester of orthophosphoric acid of the form where one ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxyanion
An oxyanion, or oxoanion, is an ion with the generic formula (where A represents a chemical element and O represents an oxygen atom). Oxyanions are formed by a large majority of the chemical elements. The formulae of simple oxyanions are determined by the octet rule. The corresponding oxyacid of an oxyanion is the compound . The structures of condensed oxyanions can be rationalized in terms of AO''n'' polyhedral units with sharing of corners or edges between polyhedra. The oxyanions (specifically, phosphate and polyphosphate esters) adenosine monophosphate ( AMP), adenosine diphosphate ( ADP) and adenosine triphosphate (ATP) are important in biology. Monomeric oxyanions The formula of monomeric oxyanions, , is dictated by the oxidation state of the element A and its position in the periodic table. Elements of the first row are limited to a maximum coordination number of 4. However, none of the first row elements has a monomeric oxyanion with that coordination number. Instead, c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cluster Chemistry
Nanoclusters are atomically precise, crystalline materials most often existing on the 0-2 nanometer scale. They are often considered kinetically stable intermediates that form during the synthesis of comparatively larger materials such as semiconductor and metallic nanocrystals. The majority of research conducted to study nanoclusters has focused on characterizing their crystal structures and understanding their role in the nucleation and growth mechanisms of larger materials. Materials can be categorized into three different regimes, namely bulk, nanoparticles and nanoclusters. Bulk metals are electrical conductors and good optical reflectors and metal nanoparticles display intense colors due to surface plasmon resonance. However, when the size of metal nanoclusters is further reduced to form a nanocluster, the band structure becomes discontinuous and breaks down into discrete energy levels, somewhat similar to the energy levels of molecules. This gives nanoclusters similar q ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
