Ward Michael D
Department of Chemistry, University of Sheffield, Sheffield, UKS3 7HF.
Chem Commun (Camb). 2009 Aug 14(30):4487-99. doi: 10.1039/b906726b. Epub 2009 Jun 10.
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.
含有两个与中心芳族间隔基相连的螯合吡唑基吡啶单元的简单双齿配体，与六配位过渡金属二价阳离子反应，导致一系列广泛的多面体笼状配合物自组装。这些包括M(4)L(6)四面体、M(8)L(12)立方体、M(12)L(18)截顶四面体和M(16)L(24)四帽截顶四面体。在所有情况下，金属与配体的比例均为2:3，这反映了六配位金属离子与四齿配体的结合。所得结构基于那些顶点与面的比例为2:3的多面体，每个顶点处有一个金属离子，每条边上有桥连配体。这些笼子展现出一系列有趣的性质，例如在较小的例子中基于阴离子的模板效应；与中心空腔相关的主客体化学；贫电子和富电子配体片段之间在外围的芳族堆积，这似乎对它们的稳定性有很大贡献；以及由于构建在配体主链中的萘基和蒽基等荧光团的芳族堆积而产生的修饰荧光性质。使用面帽（三齿配体）和边桥连（双齿配体）配体的混合物可以得到更复杂的结构类型，例如在自组装过程中选择两种类型配体组合的M(12)立方八面体的例子。
