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

由有机化合物和小金属组分组成的结构明确的杂化材料由于其固有的不同性质和可能的协同效应而成为材料科学研究的热点之一。多金属氧酸盐是早期过渡金属氧化物的阴离子簇，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有吸引力的无机建筑材料，具有广泛的应用前景。近年来，我们发现Keggin多氧钨酸盐阴离子与杯状[4]芳烃钠络合物组成的强直晶体采用多孔、单层结构等特征三维填充结构。然而，这些潜在有用的晶体材料在热处理过程中结构不稳定，导致溶剂化物分子的消除。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连锁原有的填充结构。在本研究中，我们发现使用杯状[4]芳烃下缘有两个乙氧羰基甲氧基，可以得到一个具有热稳定的一维微孔的离子晶体，由于两亲性孔环境，小醇优先被捕获。我们还发现，在紫外光照射下，由邻苯甲酰基附加的杯芳烃制备的固体杂化组合物由于固相[2+2]光二聚化而产生了含多金属氧酸的杯芳烃聚合物。红外研究表明，聚合物产物的组成与聚合前几乎相同，表明无机阴离子被困在杯芳烃-聚合物基体中。

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.