Synthesis of polyoxometalte-containing calixarene polymer via solid-state polymerization

由于有机化合物和金属小物种的不同性质和可能的协同效应，设计结构确定的杂化材料是材料科学中有趣的课题之一。聚氧乙烯酸盐是前过渡金属氧化物的阴离子簇合物，具有独特的结构和优异的酸碱、氧化还原、光化学等性质，具有广泛的应用前景。近年来，我们发现Keggin多钨酸根阴离子与杯[4]芳烃钠配合物形成的配位晶体具有独特的三维堆积结构，如多孔结构和单层结构。然而，这些潜在有用的结晶材料在结构上对导致所包含的溶剂化物分子消除的热处理不稳定。这一发现促使我们通过杯芳烃单元的分子设计来探索结构更稳定的杂化晶体，并尝试通过杯芳烃单元之间的交联来联锁原始的堆积结构。在本研究中，我们发现，使用的杯[4]芳烃具有两个乙氧基羰基甲氧基在较低的边缘给出了一个离子晶体与热稳定的一维微孔，其中小的醇被优先捕获由于两亲性的孔环境。我们还发现，从cimmamoyl附加的杯芳烃制备的固体杂化组件得到，在紫外光照射下，作为固相[2+2]光二聚的结果，含聚氧乙烯酸酯的杯芳烃聚合物。红外研究表明，聚合物产物的组成与聚合前几乎相同，表明无机阴离子被捕获在杯芳烃聚合物基质中。

The design of structurally defined hybrid materials consisting of organic compounds and small metal species is one of the interesting subjects in materials science because of their inherently different natures and possible synergetic effects. Polyoxometalates, anionic clusters of early transition metal oxides, are attractive inorganic building blocks because of their discrete structures and notable acid-base, redox, and photochemical properties that lead to a vast range of applications. Recently, we have found that the tonic crystals composed of Keggin polyoxotungstate anion and sodium complex of calix[4]arene-adopt characteristic 3D packing structures, such as porous and monolayr-like domain-separated structures. However, these potentially useful crystalline materials were structurally unstable towards the thermal treatment that causes the elimination of the included solvate molecules. This observation motivated us to explore more structurally stable hybrid crystals by the molecular design of the calixarene units, and also attempt the interlocking the original packing structures by cross-linking among the calixarene units. In the present study, we found that the use of a calix[4]arene having two ethoxycarbonylmethoxy groups at the lower rim gave a an ionic crystal with thermally stable 1D micropores, to which small alcohols were preferentially trapped due to the amphiphilic pore environment. We also found that solid hybrid assemblies prepared from cimmamoyl-appended calixarenes gave, upon UV light irradiation, polyoxometalate-containing calixarene polymers as the result of soild-phase [2+2] photodimerization. Infrared studies revealed that the composition of the polymer product is almost identical to that before polymerization, indicating that the inorganic anions were trapped within the calixarene-polymer matrix.