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Heteropolyacid
In chemistry, 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 (Mo, W) or less commonly 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 tetrahedrally-coordin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phosphotungstic Acid
Phosphotungstic acid (PTA) or tungstophosphoric acid (TPA), is a heteropoly acid with the chemical formula . It forms hydrates . It is normally isolated as the ''n'' = 24 hydrate but can be desiccated to the hexahydrate (''n'' = 6). EPTA is the name of ethanolic phosphotungstic acid, its alcohol solution used in biology. It has the appearance of small, colorless-grayish or slightly yellow-green crystals, with melting point 89 °C (24 hydrate). It is odorless and soluble in water (200 g/100 ml). It is not especially toxic, but is a mild acidic irritant. The compound is known by a variety of names and acronyms (see 'other names' section of infobox). In these names the "12" or "dodeca" reflects the fact that the anion contains 12 tungsten atoms. Some early workers who did not know the structure called it phospho-24-tungstic acid, formulating it as 3H2O·P2O5 24WO3·59H2O, , which correctly identifies the atomic ratios of P, W and O. This formula was still quoted in papers as late ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heteropolymetalate
In chemistry, 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 (Mo, W) or less commonly 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 tetrahedrally-coordinated he ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silicotungstic Acid
Silicotungstic acid or tungstosilicic acid is a heteropoly acid with the chemical formula . It forms hydrates . In freshly prepared samples, ''n'' is approximately 29, but after prolonged desiccation, ''n'' = 6. It is a white solid although impure samples appear yellow. It is used as a catalyst in the chemical industry. Applications Silicotungstic acid is used to manufacture ethyl acetate by the alkylation of acetic acid by ethylene: : It has also been commercialized for the oxidation of ethylene to acetic acid: : This route is claimed as a "greener" than methanol carbonylation. The heteropoly acid is dispersed on silica gel at 20-30 wt% to maximize catalytic ability. It has also recently been proposed as a mediator in production of hydrogen through electrolysis of water by a process that would reduce the danger of explosion while allowing efficient hydrogen production at low current densities, conducive to hydrogen production using renewable energy. Silicotungstic acid is al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Keggin Structure
Keggin structure is the best known structural form for heteropoly acids. It is the structural form of α-Keggin anions, which have 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 the most stable structure of polyoxometalate catalysts. History The first α-Keggin anion, ammonium phosphomolybdate (), was first reported by 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 valences. Tw ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has a great affinity towards oxygen, and forms a protective layer of oxide on the surface when exposed to air. Aluminium visually resembles silver, both in its color and in its great ability to reflect light. It is soft, non-magnetic and ductile. It has one stable isotope, 27Al; this isotope is very common, making aluminium the twelfth most common element in the Universe. The radioactivity of 26Al is used in radiodating. Chemically, aluminium is a post-transition metal in the boron group; as is common for the group, aluminium forms compounds primarily in the +3 oxidation state. The aluminium cation Al3+ is small and highly charged; as such, it is polarizing, and bonds aluminium forms tend towards covalency. The strong affinity tow ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phosphomolybdic Acid
Phosphomolybdic acid is the heteropolymetalate with the formula . It is a yellow solid, although even slightly impure samples have a greenish coloration. It is also known as dodeca molybdophosphoric acid or PMA, is a yellow-green chemical compound that is freely soluble in water and polar organic solvents such as ethanol. It is used as a stain in histology and in organic synthesis. Histology Phosphomolybdic acid is a component of Masson's trichrome stain. Organic synthesis Phosphomolybdic is used as a stain for developing thin-layer chromatography plates, staining phenolics, hydrocarbon waxes, alkaloids, and steroids. Conjugated unsaturated compounds reduce PMA to molybdenum blue. The color intensifies with increasing number of double bonds in the molecule being stained. Phosphomolybdic acid is also occasionally used in acid-catalyzed reactions in organic synthesis. It has been shown to be a good catalyst for the Skraup reaction for the synthesis of substituted quinolines. See ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
XM10
XM1 may refer to: * 3730 Hurban (1983 XM1), a main-belt asteroid * The Fujifilm X-M1, a mirrorless digital camera * The M1 Abrams (or XM1 prototype), a US main battle tank * The Marske XM-1, an experimental glider plane * An Sirius XM Satellite Radio broadcast satellite, XM-1 "Rock" See also * XM (other) * XMI (other) * XML (other) XML or the Extensible Markup Language is a document formatting language. XML may also refer to: * Explainable machine learning (XML), a type of artificial intelligence * Malaysian Sign Language ISO 639 language code xml * Minlaton Airport IATA ai ... {{Letter-NumberCombDisambig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Allman
{{disambiguation ...
Allman may refer to: Music *The Allman Brothers Band, Rock and Roll Hall of Fame southern rock band, formed by Duane and Gregg Allman *The Allman Joys, an early band formed by Duane and Gregg Allman *The Gregg Allman Band People *Allman (surname) Places *Allman, Indiana, a town in the US *William Allman Memorial Arena, an ice hockey arena in Stratford, Ontario, Canada Science and technology *The Allman style, an indentation style See also *Aleman (surname) *Alman (surname) Alman is an English surname of multiple origin. It can be a variant of '' Allman, Alleman'', from the Anglo-Norman for "German", or of Swedish or German ''Ahl(e)mann'', or of Jewish ''Almen'' "widower".Patrick Hanks, ''Dictionary of American Family ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
