Silver ions and organic ligands can self-assemble directly into tri- or tetra-nuclear molecular knots in a one-pot reaction
The topology of a molecule has a crucial role in determining its properties, and so the synthesis of entangled species such as knots and links has attracted considerable interest. Molecular knots can be made by using a number of different covalent or non-covalent templating strategies, but such approaches have traditionally involved multi-step syntheses.
Now, Mir Wais Hosseini, Jean-Marc Planeix and co-workers1 at the Université Louis Pasteur in France have observed the self-assembly of silver ions and organic ligands directly into molecular knots. The ligands consist of a flexible oligo-ether chain with a rigid quinoline group at each end. The two different types of coordinating sites — oxygen atoms in the linker and nitrogen atoms in the aromatic end groups — combine to wrap around a small number of silver ions to produce knotted structures when the components slowly diffuse together in a mixture of solvents. Different knotted complexes were formed depending on the length of the oligo-ether chain.
The ligand with a longer ether chain (ten carbon atoms) formed a trinuclear knot — in which three ligands combine with three silver ions — whereas the ligand with the eight-carbon-atom chain resulted in a tetranuclear knot comprising four ligands and four metal ions. In both cases, the metal centres act as connecting nodes and cannot be removed without disrupting the entire structure.
References
Bourlier, J. et al. Direct synthesis and structural characterisation of tri- and tetra-nuclear silver metallaknotanes by self-assembly approach. Chem. Commun. 10.1039/b815580a (2008).
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Pichon, A. Knot your usual molecules. Nature Chem (2008). https://doi.org/10.1038/nchem.87
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DOI: https://doi.org/10.1038/nchem.87