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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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The rare-earth dicyanamides Ln[N(CN)2]3 (Ln=La, Ce, Pr, Nd, Sm, Eu) were obtained via ion exchange in aqueous medium and subsequent drying: The crystal structures were solved and refined based on X-ray powder diffraction data and they were found to be isotypic: Ln[N(CN)2]3; Cmcm (no. 63), Z=4, Ln=La: , , ; Ce: , , ; Pr: , , ; Nd: , , ; Sm: , , ; Eu: , , ). The compounds represent the first dicyanamides with trivalent cations. The Ln3+ ions are coordinated by three bridging N atoms and six terminal N atoms of the dicyanamide ions forming a three capped trigonal prism. The structure type is related to that of PuBr3. The novel compounds Ln[N(CN)2]3 have been characterized by IR and Raman spectroscopy (Ln=La) and the thermal behavior has been monitored by differential scanning calorimetry (Ln=Ce, Nd, Eu). 相似文献