摘要:
用变温XRD，变温IR以及TG-DTA等方法，系统地研究了具有Dawson结构的YmHnP2M18O62#8226;qH2O（Y=K+, NH4+, Cu2+；M=Mo，W）的热解性质，获得了它们较为精确的热分解温度，对其热分解的判断方法提出了一些新的见解.结果表明，以钼为配位原子的Dawson结构钾盐，铵盐，铜盐分别在250 ℃, 210 ℃, 240 ℃ 发生了热重排，生成了具有Keggin结构的化合物.以钨为配位原子的钾盐在410 ℃也有相似的行为，但铵盐和铜盐却没有观察到类似的热重排现象，分别在400 ℃, 450 ℃直接热分解为WO3.这些结果显示，热重排现象的发生可能与相应的Keggin结构化合物的热稳定性有关.
Abstract:
The thermal decomposition behavior of metal-oxygen clusters with Dawson structure, YmHnP2M18O62#8226;qH2O, was systematically investigated using the X-ray power thermodiffractometry and FTIR at different temperatures, TG-DTA. The experimental results indicated that Dawson-type metal-oxygen clusters with anion,[P2Mo18O62]6-,and different counter cations,NH4+,Cu2+,K+,underwent an irreversible thermal rearrangement around 210 ℃,240 ℃,250 ℃, respectively to give the corresponding Keggin-type metal-oxygen clusters containing [PMo12O40]3-as one of the products. For the metal-oxygen clusters containing tungsten, the pyrolysis procedure of potassium salt with [P2W18O62]6-anion is similar to that of metal-oxygen clusters with [P2Mo18O62]6-anion, whenas the NH4+, Cu2+salts of [P2W18O62]6-seem to decompose directly into WO3 at 400 ℃, 450 ℃,respectively.These results testify that the thermal solid-state rearrangements of Dawson-type anions correlated with the thermal stability of the corresponding Keggin-type compounds. Furthermore, some proposals about the criterion and the adjudication of thermal decomposition temperature for metal-oxygen clusters with different thermal decomposition behavior are also given.
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