8 Legs or 8 Faces?

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Science  31 Jul 2009:
Vol. 325, Issue 5940, pp. 518
DOI: 10.1126/science.325_518d

Octopi are so named because these intriguing sea creatures have eight legs. Lu et al. have prepared an “octapi” supramolecular complex, so named because it assembles through the stacking interactions of eight faces—more specifically, the faces of aromatic rings bearing delocalized pi-bonded electrons. The authors mixed palladium ions in solution with phenyl-substituted phosphine ligands and pyridine-substituted pyrazole ligands. When the latter ligands were properly sized (with a two-carbon bridge linking a pair of pyridylpyrazoles), crystals formed in which, at the molecular scale, two tightly interlocked macrocycles were held together by a 2.5-nm-long column of stacking interactions involving eight phenyl and pyridyl faces, supplementing phosphorus and pyridyl-nitrogen coordination to the metal centers. Extending the pyrazole bridge length by one carbon disrupted the geometric balance, leading to separated (rather than linked) macrocycles in the resultant crystal lattice.

J. Am. Chem. Soc. 131, 10.1021/ja9041912 (2009).

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