Forging a carbon nanobelt

Rings of carbon atoms can be fashioned into balls, tunnels, and sheets. Yet before the discoveries of fullerenes, carbon nanotubes, and graphene, chemists dreamed of building a different carbon-ringed structure: a loop of edge-sharing benzene molecules. Now, more than six decades after it was proposed, Guillaume Povie and colleagues at Nagoya University in Japan have created the elusive carbon nanobelt.

The researchers started by combining an aldehyde and a benzylic bromide. Using a series of creative chemical reactions, some of which had rarely been employed before, Povie and colleagues assembled building blocks, joined them together to form a ring, and then introduced additional bonds that solidified the belt configuration. X-ray crystallography measurements confirmed a roughly 8-Å-diameter nanobelt structure made up of a single strand of 12 benzene rings, as shown here. The hexagonal panels stand perpendicular to the cross-sectional plane of the belt, like the slats of a fence surrounding a garden.

The researchers performed fluorescence, light-absorption, and Raman spectroscopy measurements on their creation and found similarities to a metallic, single-walled nanotube that has the same diameter and orientation of benzene rings. The resemblances are especially notable because of the new nanobelt’s potential to serve as a template from which to grow those (6,6) nanotubes. Current fabrication methods tend to produce a hodgepodge of nanotube species, each with different electronic and thermal properties. The new nanobelt, which is, in effect, an ultrashort nanotube open on both ends, could form the basis of a production method that yields uniform tubes. Povie and colleagues are working on ways to stack nanobelts to build lengthy nanotubes. (G. Povie et al., Science 356, 172, 2017, doi:10.1126/science.aam8158 .)