Molecular Tinkertoys Yield a Box

Imagine building a house out of rope. It wouldn’t be easy. Neither is building individual molecules into rigid, hollow shapes. In fact, one of the most simple of molecular geometries-a stand-alone cube-has so far eluded scientists.

Now, Thomas Rauchfuss, a chemist at the University of Illinois at Urbana-Champaign, and his co-workers have constructed a molecular box that measures 5 angstroms on a side and 132 cubic angstroms in volume. Big enough to hold single atoms inside. The ability to trap atoms could one day enable the molecular box to function as a highly sensitive sensor.

The key to molecular box-building is a Tinkertoy strategy alternating two types of corners, explains Rauchfuss. One type of corner is a cobalt atom studded with carbon arms; the other type is a rhodium atom with nitrogen appendages. The carbon and nitrogen groups connect to form a stable cube. What’s more, says Rauchfuss, the boxes are constructed in a way that allows them to exist as separate molecules.

The box joins a growing list of molecular shapes made by chemists in recent years. Examples include fullerenes-60 carbon atoms arranged like a geodesic sphere-and pipette-like carbon nanotubes. And there’s no reason to stop at a box, says Rauchfuss. “We might make a bowl or maybe a giant tetrahedron next.”