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排序方式: 共有169条查询结果,搜索用时 93 毫秒
1.
Lisheng Chi Ian Swainson Jae-Hyuk Her Osvald Knop 《Journal of solid state chemistry》2005,178(5):1376-1385
The perovskite-structured compound methylammonium lead chloride orders into a low-temperature phase of space group Pnma, in which at 80 K each of the orthorhombic axes , and is doubled with respect to the room temperature disordered cubic phase (). The structure was solved by ab initio methods using the programs EXPO and FOX. This unusual cell basis for space group Pnma is not that of a standard tilt system. This phase, in which the methylammonium ions, are ordered shows distorted octahedra. The octahedra possess a bond angle variance of 60.663°2 and a quadratic elongation of 1.018, and are more distorted than those in the ordered phase of methylammonium lead bromide. There is also an alternating long and short Pb-Cl bond along a, due to an off-center displacement of Pb within the octahedron. This suggests that the most rigid unit is actually the methylammonium cation, rather than the PbCl6 octahedra, in agreement with existing spectroscopic data. 相似文献
2.
Sherif El-Basil Gani Jashari Jan V. Knop Nenad Trinajstić 《Monatshefte für Chemie / Chemical Monthly》1984,115(11):1299-1312
The reduced graph model, when used in conjunction with the search trees method, provides a novel combinatorial procedure for the enumeration and generation ofKekulé structures. The procedure is suited for large benzenoid hydrocarbons consisting of cata- and thin peri-condensed parts.
Zur Anwendung des Reduced Graph Model im Zusammenhang mit Search Trees zur Ermittlung der Anzahl möglicherKekulé-Strukturen
Zusammenfassung Das Modell erlaubt mit der im Titel genannten Kombination eine neuartige Methode zur Ermittlung und Generierung vonKekulé-Strukturen. Das Verfahren ist für große benzoide Kohlenwasserstoffe geeignet, die aus cata- und (dünnen) peri-kondensierten Teilstrukturen bestehen.相似文献
3.
M. Althoff W. Braunschweig F.J. Kirschfink H.-U. Martyn P. Rosskamp D. Schmitz H. Siebke W. Wallraff J. Eisenmann H.M. Fischer H. Hartmann A. Jocksch G. Knop H. Kolanoski H. Kück V. Mertens R. Wedemeyer G. Zobernig 《Physics letters. [Part B]》1984,149(6):524-532
We have determined the average lifetime of hadrons containing b quarks produced in e+e? annihilation to be . Our method uses charged decay products from both non-leptonic and semileptonic decay modes. 相似文献
4.
Osvald Knop 《Journal of solid state chemistry》1982,45(2):223-234
It is shown how the 6:(3 + 3)-coordinated AB2 layer structure of the C 19 type can be derived by continuous rhombohedral distortion from the cubic 8:8-coordinated C 1-type structure. The magnitude of the distortion actually observed (as manifested in the ratio per AB2 layer, R1) is considered in relation to geometric factors, with particular attention to the competing CdI2 (C 6) structure type. Reasons are suggested for the nonoccurrence of the C 19 structure type among M(OH)2 and of the anti-C 19 type among the simple hexahalometallates(IV), A2MX6. Finally, the structures of alkylammonium hexahalometallates(IV), (RnNH4?n)2MX6, are surveyed to demonstrate how the charge arrangements of the composite cations and anions in these compounds are able to mimic the structure types encountered with simple AB2 compounds. 相似文献
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Marcel Meury Matthias Knop Florian P. Seebeck 《Angewandte Chemie (International ed. in English)》2017,56(28):8115-8119
The formylglycine-generating enzyme (FGE) is a unique copper protein that catalyzes oxygen-dependent C−H activation. We describe 1.66 Å- and 1.28 Å-resolution crystal structures of FGE from Thermomonospora curvata in complex with either AgI or CdII providing definitive evidence for a high-affinity metal-binding site in this enzyme. The structures reveal a bis-cysteine linear coordination of the monovalent metal, and tetrahedral coordination of the bivalent metal. Similar coordination changes may occur in the active enzyme as a result of CuI/II redox cycling. Complexation of copper atoms by two cysteine residues is common among copper-trafficking proteins, but is unprecedented for redox-active copper enzymes or synthetic copper catalysts. 相似文献
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Quasielastic neutron scattering experiments on TMNB show for T > 2.8 K a diffraction pattern characteristic for a 1-D ferromagnet with an exchange energy along the chain J/kB ? 10 K. For T < TN =2.7 K the 3-D magnetic ordering was found to be of a simple antiferromagnetic type. A lattice distortion was observed as well below 200 K. 相似文献
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