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1Author    Requires cookie*
 Title    Über Isopolymolybdatfeststoffe und deren Beziehung zu Isopolymolybdationen in wäßriger Lösung* Concerning Solid Isopolym olybdates an d th e ir R elation to Isopolym olybdate Ions in Aqueous Solution  
 Abstract    After a brief discussion on the output capacity of the methods used for the study of the isopolymetalates, a classification and characterization of the solid isopolymolybdates obtainable from aqueous solution is given, and the relation of the solid isopolymolybdates to the isopolymolybdate ions in solution is studied. A correlation between the occurrence or non-occurrence of a species in a solid and in its solution detectable by Raman spectro­ scopy, the solubility of the solid, and the time necessary for the formation of the solid was found. This gives important informations on the mechanisms of formation of the iso-polym etalate ions. The m ost remarkable result of this investigation is that contrary to the view of the majority of the papers on this subject the octamolybdate ion Mo80 264_ having the structure found by L i n d q v i s t does not occur in important quantities in solution at room temperature. For setting up a reaction scheme on the isopolymolybdates only very few of the confusing multiplicity of the papers give evidentiary informations. Most of the papers are overinterpreted. 
  Reference    (Z. Naturforsch. 30b, 471—484 [1975]; eingegangen am 21. Februar 1975) 
  Published    1975 
  Keywords    Isopolyanions, Isopolymolybdates, Fingerprint Raman Spectroscopy, Reaction Mechanisms 
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 TEI-XML for    default:Reihe_B/30/ZNB-1975-30b-0471.pdf 
 Identifier    ZNB-1975-30b-0471 
 Volume    30 
2Author    Karl-Heinz TytkoRequires cookie*
 Title    Über den Mechanismus der Bildung von Polyanionen in wäßriger Lösung. Zum Bildungsmechanismus eines Polytetramolybdations [Mo4014 4-]» On the Mechanism of Formation of Polyanions in Aqueous Solution. Concerning the Mechanism of Formation of a Polytetramolybdate Ion [Mo4014 4 ~]«  
 Abstract    Possible structures and the pertinent reaction pathways for the polymetalate ion present in a slightly soluble polymetalate having the analytical formula A20 • 2 MO3 have been derived on the basis of theoretical considerations. Structure and kind of combination of the tetrameric units of one of the possibilities are in agreement with the results of X-ray structure analyses. First the previously proposed planar tetrametalate ion [M40i2(0H)4] 4_ is formed by stepwise aggregation according to an addition mechanism. This species undergoes a rearrangement of the coordination sphere of two of the M atoms and is then subject to a poly condensation resulting in a polytetrametalate chain, [M40i4 4_ ]n. 
  Reference    (Z. Naturforsch. 31b, 737—748 [1976]; eingegangen am 2. Januar/16. Dezember 1975) 
  Published    1976 
  Keywords    Isopolyanions, Isopolymolybdates, Reaction Mechanisms, Polymetalate Structures 
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 TEI-XML for    default:Reihe_B/31/ZNB-1976-31b-0737.pdf 
 Identifier    ZNB-1976-31b-0737 
 Volume    31 
3Author    R. K. Broszkiewicz+, T. Söylemez, D. Schulte-FrohlindeRequires cookie*
 Title    Reactions of OH Radicals with Acetylacetone in Aqueous Solution. A Pulse Radiolysis and Electron Spin Resonance Study  
 Abstract    Pulse radiolysis experiments monitoring optical absorbance as well as conductivity and in-situ ESR radiolysis studies show that the OH radical reacts with the enol (k = 8.6 x 10 9 M _1 s _1) and the enolate (k = 7.4 X 10 9 M _1 s -1) forms of acetylacetone by addition to the C = C double bond in aqueous N2O saturated solution. The OH reaction with enol leads to equal amounts of two radicals, CH3COCHOHCOHCH3 (2) and CH3COCHC(OH)2CH3 (4), as determined by scavenger reactions. At pH less than 1 the radical CH3COCHCOCH3 (1) is observed by ESR spectroscopy showing that radical 2 and/or 4 eliminate water by proton catalyzed reactions. Under alkaline condition the OH adducts to the enolate eliminate OH -with rate constants larger than 10 5 s -1 leading to radical 1. G(OH") is determined to be 5.6 showing that addition is the main reaction of OH with enolate. To a much smaller degree the OH radical is proposed to abstract an H atom from that CH3 group which is attached to the C —C double bond in enol and enolate, producing substituted allyl radicals which absorb in the visible region. The reaction of OH with the keto form has not been observed indicating that the rate constant of this reaction is significantly smaller than those with enol and enolate. 
  Reference    Z. Naturforsch. 37b, 368—375 (1982); received August 19 1981 
  Published    1982 
  Keywords    Pulse Radiolysis, OH Radicals, Acetylacetone, Reaction Mechanisms 
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 TEI-XML for    default:Reihe_B/37/ZNB-1982-37b-0368.pdf 
 Identifier    ZNB-1982-37b-0368 
 Volume    37 
4Author    Paolo Ghigna, M. Arco, ScaviniRequires cookie*
 Title    Kinetics and Mechanism of Nd2C u04 Synthesis  
 Abstract    The reaction N d20 3 -I-C uO -*■ N d 2C u 0 4 was investigated on the basis of the Wagner-Schmalz-ried theory of diffusion-driven reactions between crystalline solids, with the help of monodimen­ sional chemical diffusion measurements. It was found that the kinetics of the process is governed by C u2+ diffusion, and the chemical diffusion coefficient Z)(Cu2+) in the N d 2C u 0 4 matrix was obtained (9.9 • 10-13, 1.97 • 10-12 and 1.98 • 10" 11 cm 2 s -1 at 1223, 1273 and 1323 K, respectively). The rela­ tively low value of D (C u2+) was interpreted on the basis of the crystal structures of the compound and related materials, which in addition may suggest an alternative rationale for the interpretation of neodymium immobility. 
  Reference    Z. Naturforsch. 49a, 611—616 (1994); received M arch 14 1994 
  Published    1994 
  Keywords    N d 2C u 0 4 superconductor, Synthesis, Reaction mechanism, Kinetics, Chemical diffu­ sion 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0611.pdf 
 Identifier    ZNA-1994-49a-0611 
 Volume    49