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A novel mixed cadmium zirconium cesium oxalate with an open architecture has been synthesized from precipitation methods at room pressure. It crystallizes with an hexagonal symmetry, space group P3112 (no. 151), a=9.105(5) Å, c=23.656(5) Å, V=1698(1) Å3 and Z=3. The structure displays a [CdZr(C2O4)4]2− helicoidal framework built from CdO8 and ZrO8 square-based antiprisms connected through bichelating oxalates, which generates channels along different directions. Cesium cations, hydronium ions and water molecules are located inside the voids of the anionic framework. They exhibit a dynamic disorder which has been further investigated by 1H and 133Cs solid-state NMR. Moreover a phase transition depending both upon ambient temperature and water vapor pressure was evidenced for the title compound. The thermal decomposition has been studied in situ by temperature-dependent X-ray diffraction and thermogravimetry. The final product is a mixture of cadmium oxide, zirconium oxide and cesium carbonate. 相似文献
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Takahiro Iijima Keigo Hamada Kazunaka Endo 《Journal of Physics and Chemistry of Solids》2005,66(6):1101-1106
The temperature dependences of 2H NMR spectra and spin-lattice relaxation time T1 have been measured for paramagnetic [Mn(H2O)6][SiF6]. The obtained 2H NMR spectra were simulated by considering the quadrupole interaction and paramagnetic shift. The variation of the spectra measured in phase III was explained by the 180° flip of water molecules. The activation energy Ea and the jumping rate at infinite temperature k0 for the 180° flip of H2O were obtained as 35 kJ mol−1 and 4×1014 s−1, respectively. The spectral change in phases I and II was ascribed to the reorientation of [Mn(H2O)6]2+ around the C3 axis where the Ea and k0 values were estimated as 45 kJ mol−1 and 1×1013 s−1, respectively. From the almost temperature independent and short T1 value, the correlation time for electron-spin flip-flops, τe, and the exchange coupling constant J were obtained as 3.0×10−10 s and 2.9×10−3 cm−1, respectively. The II-III phase transition can be caused by the onset of the jumping motion of [Mn(H2O)6]2+ around the C3 axis. 相似文献
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Edward Mikuli ?ukasz Hetmańczyk Aneta Kowalska 《Journal of Physics and Chemistry of Solids》2007,68(1):96-103
Middle infrared absorption, Raman scattering and proton magnetic resonance relaxation measurements were performed for [Zn(NH3)4](BF4) in order to establish relationship between the observed phase transitions and reorientational motions of the NH3 ligands and BF4− anions. The temperature dependence of spin-lattice relaxation time (T1(1H)) and of the full width at half maximum (FWHM) of the bands connected with ρr(NH3), ν2(BF4) and ν4(BF4) modes in the infrared and in the Raman spectra have shown that in the high temperature phase of [Zn(NH3)4](BF4)2 all molecular groups perform the following stochastic reorientational motions: fast (τR≈10−12 s) 120° flips of NH3 ligands about three-fold axis, fast isotropic reorientation of BF4− anions and slow (τR≈10−4 s) isotropic reorientation (“tumbling”) of the whole [Zn(NH3)4]2+ cation. Mean values of the activation energies for uniaxial reorientation of NH3 and isotropic reorientation of BF4− at phases I and II are ca. 3 kJ mol−1 and ca. 5 kJ mol−1, respectively. At phases III and IV the activation energies values for uniaxial reorientation of both NH3 and of BF4− equal to ca. 7 kJ mol−1. Nearly the same values of the activation energies, as well as of the reorientational correlation times, at phases III and IV well explain existence of the coupling between reorientational motions of NH3 and BF4−. Splitting some of the infrared bands at TC2=117 K suggests reducing of crystal symmetry at this phase transition. Sudden narrowing of the bands connected with ν2(BF4), ν4(BF4) and ρr(NH3) modes at TC3=101 K implies slowing down (τR?10−10 s) of the fast uniaxial reorientational motions of the BF4− anions and NH3 ligands at this phase transition. 相似文献