Science 344, 499–504 (2014)

Non-covalent interactions such as hydrogen bonds and π–π interactions can be used to build intricate self-assembled nanostructures. These interactions are typically weaker than covalent bonds and the steps of the assembly process can be reversible, allowing 'errors' to be corrected and for highly ordered structures to be created. Manipulating the nanostructures once they are assembled is, however, a significant challenge. Takuzo Aida and colleagues in Japan have now shown that ferrocene-based building blocks can be self-assembled into nanotubes and then disassembled into individual nanorings by altering the non-covalent interactions between the components.

Ferrocene is a sandwich compound in which two cyclopentadienyl (C5H5) rings are bonded to opposite sides of an iron atom. Two aromatic arms, with metal-coordinating pyridyl groups (RC5H4N) at their ends, are attached to each of the cyclopentadienyl rings, and in the presence of silver ions, the building blocks can self-assemble into metal–organic nanotubes with diameters of around 7 nm and 13 nm, depending on the size of the pyridyl arms. The nanotubes can then be sliced into their constituent nanorings through oxidation of the ferrocene groups, which reduces the attractive interaction between the rings. The researchers also show that the nanorings can be transferred onto substrates electrostatically or reassembled into nanotubes through reduction of the ferrocene groups.