The structure and thermal behaviour of some long chain cerium(III) carboxylates
The structure and thermal behaviour of some long chain cerium(III) carboxylates
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DOI：
10.1039/a800326b
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发表时间：
1998-06-21
期刊：
影响因子：
--
通讯作者：
Miguel, MD
中科院分区：
文献类型：
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作者：
Marques, EF;Burrows, HD;Miguel, MD
通过复分解反应合成了从辛酸酯到十八酸酯的均匀链长的羧酸铈（III）。热重分析表明，存在配位水的短链同系物，而较长链的只含有吸附水。X-射线衍射和红外光谱测量表明，固相具有层状，双层结构与平面的铈（III）离子协调的羧酸基团。用DSC和偏光显微镜研究了羧酸盐的相行为。在70-120 ℃的温度范围内观察到一种或多种中间相，并且在130 - 150 ℃之间发生熔融。在偏光显微镜上观察到的织构清楚地显示了中间相的各向异性性质。虽然这些化合物的熔融的总焓和熵随着链长的增加而增加，但是这些值显著低于对于烷基链的完全熔融的预期。链的熔化和金属-羧酸盐配位区域的变化之间的竞争是负责在短链和长链衍生物之间的相行为中观察到的差异的主要因素。
The even chain length cerium(III) carboxylates from the octanoate to the octadecanoate have been synthesised by metathesis. Thermogravimetry shows the presence of coordinated water for the short chain homologues, whereas the longer chain ones only contain adsorbed water. X-Ray diffraction and IR spectral measurements show that the solid phase has a lamellar, bilayer structure with planes of the cerium(III) ions coordinated to the carboxylate groups. The phase behaviour of the carboxylates has been studied by DSC and polarized-light microscopy. One or more mesophases are observed over the temperature range 70-120 degrees C and melting occurs between 130 and 150 degrees C. The textures observed on the polarizing microscope clearly show the anisotropic nature of the mesophases. Although the overall enthalpy and entropy of melting of these compounds increase with increasing chain length, the values are considerably lower than expected for complete fusion of the alkyl chains. Competition between melting of the chains and changes in the metal-carboxylate coordination region is the major factor responsible for the differences observed in the phase behaviour between the short and long chain derivatives.