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Boron molecules that look like fullerenes.

It didn't take Harvard chemist William N. Lipscomb long to pick up on the link between boron molecules and the hollow, 60-carbon molecule called the buckyball. In 1976, he had predicted that a molecule with 32 boron exhibit an icosahedral atoms would exhibit an icosahedral structure not unlike the buckyball's soccerball shape, though that molecule had yet to be detected. Lipscomb also knew of smaller boron compounds that resembled other carbon molecules: For example, the eight-carbon cubane matches with a six-boron hydride ion.

Now lipscomb and Lou Massa, a materials scientist at Hunter College in New York City, have taken a systematic look at the possible correspondence between boron molecules and fullerences, the new class of all-carbon molecules that includes the buckyball. In the June 10 INORGANIC CHEMISTRY, they describe how a one-to-one match between the faces of one type and the vertices of the other leads to similar shapes and symmetries in these molecules. They use a classical law in geometry to predict matches.

In the boron hydrides, the boron atoms bond to each other to form a particular shape and are the atoms considered in the researchers' comparisons with carbon molecules. The hydrogen atoms radiate from these boron cages.

Superimposing the two molecules, the buckyball's 60 atoms would match up with the boron compound's 60 faces, while each of the 32 boron atoms would fall smack in the middle of the faces formed by the buckyball's carbon atoms, says Lipscomb.

The Descartes-Euler formula describes the fit between the two types of molecules. It sums the number of faces and the number of atoms -- which represent the vertices -- and subtracts two to get the number of contacts. In closed geometrical stuctures, contacts represent the connecting lines between verices; in molecules, they represent the shortest distances between neighboring atoms.

Like fullerences, hollw boron molecules should have usefull new properties, Lipscomb and Massa say. They recommend that chemists try to make closed boron hydrides using lasers to vaporize a calcium boron compound in the presence of hydrogen.
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Author:Pennesi, Elizabeth
Publication:Science News
Article Type:Brief Article
Date:Jun 20, 1992
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