Polynuclear coordination cages
Polynuclear coordination cages
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DOI：
10.1039/b906726b
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发表时间：
2009-01-01
影响因子：
4.9
通讯作者：
Ward, Michael D.
中科院分区：
文献类型：
--
作者：
Ward, Michael D.
简单的双齿配体（包含两个连接到中心芳香族间隔基的螯合吡唑基吡啶单元）与六配位过渡金属双阳离子的反应导致一系列广泛的多面体笼配合物的自组装。这些包括 M(4)L(6) 四面体、M(8)L(12) 立方体、M(12)L(18) 截断四面体和 M(16)L(24) 四帽截断四面体。在所有情况下，金属：配体比率为2：3，反映了六配位金属离子与四齿配体的结合。所得结构基于顶点与面的比例为 2:3 的多面体，每个顶点都有一个金属离子，每个边缘都有桥接配体。这些笼子显示出一系列有趣的特性，例如在较小的例子中基于阴离子的模板效应；与中心腔相关的主客体化学；贫电子和富电子配体片段之间的芳香族堆积在外围，这似乎对其稳定性有很大贡献；以及由荧光团（例如内置于配体主链中的萘基和蒽基）的芳族堆积产生的改进的荧光特性。使用面封端（三二齿）和边缘桥接（双二齿）配体的混合物可以获得更复杂的结构类型，例如 M(12) 立方八面体的例子，它在自组装过程中选择两种配体的组合。
Reaction of simple bis-bidentate ligands, containing two chelating pyrazolyl-pyridine units connected to a central aromatic spacer, with six-coordinate transition metal dications results in self-assembly of an extensive series of polyhedral cage complexes. These include M(4)L(6) tetrahedra, M(8)L(12) cubes, M(12)L(18) truncated tetrahedra and M(16)L(24) tetra-capped truncated tetrahedra. In all cases the metal : ligand ratio is 2 : 3, reflecting the combination of six-coordinate metal ions with tetradentate ligands. The resulting structures are based on those polyhedra which have a 2 : 3 ratio of vertices to faces, with a metal ion at each vertex and bridging ligand spanning each edge. The cages display a range of interesting properties such as an anion-based template effect in the smaller examples; host-guest chemistry associated with the central cavity; aromatic stacking around the periphery between electron-poor and electron-rich ligand fragments which appears to contribute substantially to their stability; and modified fluorescence properties arising from the aromatic stacking of fluorophores such as naphthyl and anthracenyl groups built into the ligand backbone. Even more complex structural types are available using a mixture of face-capping (tris-bidentate) and edge-bridging (bis-bidentate) ligands, such as examples of M(12) cuboctahedra which select a combination of two types of ligand during the self-assembly process.