共查询到20条相似文献,搜索用时 31 毫秒
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Michael Scholten 《Journal of solid state chemistry》2003,174(2):349-356
The mixed-valent compound In4Br7 undergoes a higher-order phase transition below which leads to a decrease in symmetry from the trigonal to the monoclinic (C2/c) system via . The phase transition has been monitored by X-ray powder diffraction using a linear position-sensitive detector between 15 and , and the crystal structures at room temperature and at 90 K have been refined by means of time-of-flight neutron powder-diffraction data; at , the lattice parameters are , , , and β=98.20(1)°; the new unit cell contains 88 atoms (Z=8) of which 12 are symmetry-independent. Due to their electronic instability because of a second-order Jahn-Teller effect, two of the three crystallographically independent monovalent indium cations are severely affected by the phase transition with respect to their coordination spheres; bond-valence calculations reveal significant strengthening of In+-Br− bonding upon symmetry reduction. Structural changes and group-subgroup relationships as well as possible intermediate phases are discussed. 相似文献
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Ilona Turowska-Tyrk Karolina Grze?niak El?bieta Trzop Tomasz Zych 《Journal of solid state chemistry》2003,174(2):459-465
We studied the [2+2]-photodimerization in crystals of pyridine analogs and hydroxy derivatives of chalcone using the X-ray structure analysis. The mutual orientation of adjacent molecules in the crystals was analyzed in a quantitative way and the results were compared with data for known photoactive crystals undergoing the [2+2]-photodimerization. In the case of one pyridine analog, we processed the single-crystal-to-single-crystal photodimerization and determined the structure for the mixed crystal containing both the substrate and the product. We also explained a role of hydrogen bonds in the [2+2]-photodimerization in the case of the hydroxy derivatives of chalcone. C5H4N-CO-CHCH-C6H5: , , , β=91.318(10)°, monoclinic, . The irradiated crystal of the above analog: , , , β=91.870(10)°, monoclinic, . C6H5-CO-CHCH-C5H4N: , , , β=110.01(3)°, monoclinic, C2/c,Z=8. C6H5-CO-CHCH-C6H4(o-OH): , , , β=109.73(5)°, monoclinic, . C6H5-CO-CHCH-C6H4(p-OH): , , , orthorhombic, . 相似文献
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