Blogging a crystal structure a day in 2014


Contributed by

Stuart Batten

What’s in a name? The Octapi Catenane

Prof. Batten tells us about one of the molecules that his group cooked up.


Chemists love to give names to things. Sometimes to explain a new concept or phenomenon, sometimes to make a discussion easier, and sometimes to just amuse ourselves and others. So when we discovered the structure shown here, we couldn't resist. But more on that later. I need to give some background first. 

The structure is a type of molecule called a catenane. It consists of two ring-shaped molecules that are locked together like rings in a chain. This unusual arrangement of molecules, while fascinating, does not happen by accident. Usually there are weak interactions between the molecules (much weaker than the bonds that define the molecules themselves) that encourage them to associate and form with this particular arrangement. In this case there are flat parts of the molecules called aromatic rings (look for the hexagons in the picture) that like to stack roughly parallel to each other. This is called π-stacking (so-named for the π electron clouds above and below the rings that facilitate this arrangement), and in this catenane there are eight aromatic rings, four from each molecule, that stack through the centre of the structure and stabilise this unusual entanglement of molecules.

So we decided to amuse ourselves by christening this interaction of the eight π (pi) rings stacked through the structure an "Octapi" interaction. We were then delighted when the prestigious journal Science took a shine to our structure, reporting it as an "Editor's pick" of all the papers published that week. They even highlighted it with a picture. Of an octopus. Perhaps we outsmarted ourselves…


"Octapi Interactions: Self-Assembly of a Pd-Based [2]-Catenane Driven by Eight-Fold p-Interactions", Jinzhen Lu, David R. Turner, Lindsay P. Harding, Lindsay T. Byrne, Murray V. Baker and Stuart R. Batten, J. Am. Chem. Soc., 2009, 131, 10372. DOI: 10.1021/ja9041912

See also Science, 2009, 325, 518 (DOI:10.1126/science.325_518d).

CCDC Deposition code: 731890

Tags: molecular   catenane