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Issue 30, 2009
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Polynuclear coordination cages

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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 M4L6 tetrahedra, M8L12 cubes, M12L18 truncated tetrahedra and M16L24 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 M12 cuboctahedra which select a combination of two types of ligand during the self-assembly process.

Graphical abstract: Polynuclear coordination cages

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Publication details

The article was received on 02 Apr 2009, accepted on 08 May 2009 and first published on 10 Jun 2009

Article type: Feature Article
DOI: 10.1039/B906726B
Chem. Commun., 2009, 4487-4499

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    Polynuclear coordination cages

    M. D. Ward, Chem. Commun., 2009, 4487
    DOI: 10.1039/B906726B

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