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

由有机化合物和小金属物种组成的结构明确的杂化材料的设计是材料科学中感兴趣的课题之一，因为它们具有内在的不同性质和可能的协同效应。多金属氧酸盐是早期过渡金属氧化物的阴离子簇合物，由于其离散的结构和显著的酸碱、氧化还原和光化学性质而成为吸引人的无机构建块，导致了广泛的应用。最近，我们发现由Keggin多氧钨酸根阴离子和杯[4]芳烃钠络合物组成的激元晶体具有独特的三维堆积结构，如多孔性和类单层的磁区分离结构。然而，这些潜在有用的晶体材料在结构上对导致所包含的溶剂酸盐分子消除的热处理是不稳定的。这一观察结果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。在目前的研究中，我们发现在下缘含有两个乙氧基甲氧基的杯[4]芳烃可以得到具有热稳定的一维微孔的离子晶体，由于两亲孔环境，小分子醇优先被捕获到其中。我们还发现，在紫外光照射下，通过固相[2+2]光二聚反应制备的含杯芳烃的含氧多酸聚合物的固体杂化组装。红外光谱研究表明，聚合物产物的组成与聚合前几乎相同，说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.