Solid-State Crystal-to-Crystal Phase Transitions and Reversible Structure–Temperature Behavior of Phosphovanadomolybdic Acid, H5PV2Mo10O40

The crystal packing and secondary
structure of H5PV2Mo12O40 was followed by careful X-ray
diffraction studies that revealed four unique structures and three
solid phase transitions at temperatures between 25 and 55 °C,
with loss of solvated water and concomitant contraction of the volume
and increase of the packing density. Above 60 °C H5PV2Mo12O40 becomes amorphous and
then anhydrous although the polyoxometalate cluster is stable indefinitely
up to 300 °C. Above this temperature, combined IR, Raman, XRD,
and XPS measurements show the decomposition of H5PV2Mo12O40 to crystalline MoO3 and probably amorphous vanadium oxide and vanadylphosphate, the
latter appearing to cover the surface of MoO3. Importantly,
H5PV2Mo12O40 can be easily
recovered by dissolution in water at 80 °C.

对H5PV2Mo12O40的晶体堆积和二级结构进行了细致的X射线衍射研究，揭示了其在25至55°C温度范围内存在四种独特的结构及三种固态相变，伴随溶剂水的丢失、体积收缩及堆积密度的增加。在60°C以上，H5PV2Mo12O40转变为非晶态，尽管多氧化物簇在300°C以下保持无限期的稳定。在此温度之上，结合红外、拉曼、X射线衍射及X射线光电子能谱测量，显示出H5PV2Mo12O40分解为晶态MoO3以及可能的非晶态五氧化二钒和钒磷酸盐，后者似乎覆盖了MoO3的表面。值得注意的是，H5PV2Mo12O40可通过在80°C水中溶解轻易回收。