Calorimetric and single crystal X-ray study of the phase transition of (PyH)2PdCl4
Calorimetric and single crystal X-ray study of the phase transition of (PyH)2PdCl4
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DOI：
10.1016/j.jpcs.2004.11.008
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发表时间：
2005-05-01
影响因子：
4
通讯作者：
Oguni, M
中科院分区：
文献类型：
--
作者：
Asaji, T;Fujimori, H;Oguni, M
通过热容测量和单晶X射线结构分析研究了四氯钯酸吡啶盐的多晶型转变。在240 K时，在热容的温度依赖性中检测到一个大的Alzada型异常。低温相（LTP）属于棒上的三斜晶系空间群P（1），在100 K时a = 6.856（1），B = 7.293（1），c = 7.721（1）埃，α = 75.180（2）度，β = 71.081（2）度，γ = 81.109（3）度，高温相（HTP）在bar上属于同一空间群P（1），a = 7.217（2），B = 7.470（2），c = 7.880（2）埃，α = 73.438（3）度，β = 65.195（3）度，293 K时γ = 82.727（4）度。吡啶阳离子在LTP中是反铁电有序的。然而，在HTP中，观察到阳离子的取向无序。本文结合单晶X射线衍射和热容的测量结果以及核磁共振氢谱的测量结果，讨论了HTP中吡啶离子重取向的威尔斯势阱间的能量差。五位无序模型与H-1 NMR和X-射线研究的结果一致。(c)2005爱思唯尔有限公司保留所有权利。
Polymorphic transition of pyridinium tetrachloropalladate(II) was investigated by heat capacity measurements and by single crystal X-ray structural analysis. A large lambda-type anomaly was detected at 240 K in the temperature dependence of the heat capacity. The low-temperature phase (LTP) belongs to the triclinic space group P (1) over bar with a = 6.856(1), b = 7.293(1), c = 7.721 (1) angstrom, alpha = 75.180(2)degrees, beta = 71.081(2)degrees, gamma = 81.109(3)degrees at 100 K, and the high-temperature phase (HTP) to the same space group P (1) over bar with a = 7.217(2), b = 7.470(2), c = 7.880(2) angstrom, alpha = 73.438(3)degrees, beta = 65.195(3)degrees, gamma = 82.727(4)degrees at 293 K. The pyridinium cations are ordered antiferroelectrically in LTP. In HTP, however, an orientational disorder of the cation was observed. The energy difference between potential wells for the reorientation of pyridinium ion in HTP is discussed referring to the results of the present single crystal X-ray and heat capacity as well as the previous H-1 NMR measurements. A five-site disorder model is shown to be consistent with both of the observations of H-1 NMR and X-ray study. (c) 2005 Elsevier Ltd. All rights reserved.