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Sunday, January 17, 1999 Published at 10:54 GMT


Sci/Tech

Chemical cages

The MoS2 cage (sulphur atoms not shown)

US scientists think they have produced what may be among the first "inorganic fullerenes". This would mark another step forward in what has become one of the most fashionable areas of chemistry.

Fullerenes - carbon molecules of a certain size that have assembled themselves into cage-like structures - were first discovered in 1985. C60 is the most famous example - 60 carbon atoms linked together in 12 pentagons and 20 hexagons and looking rather like a soccer ball.

These "buckyballs", as they are called, have unique properties and applications are envisaged in everything from superconductors to superlubricants. Fullerenes have opened up a whole new field for study.

The search is also on for non-carbon, or inoragnic, materials that will perform the same trick. And whilst some labs have managed to produce cages from substances like boron nitride and molybdenum disulphide (MoS2), their structures have not displayed the specific sizes and geometries shown in the carbon fullerenes.

Closed-cage octahedra

But now researchers from the National Renewable Energy Laboratory (NREL) in Golden, Colorado, look to be making progress towards the first true inorganic fullerenes.


[ image: Harry Kroto shared the Nobel Prize for his part in discovering C60]
Harry Kroto shared the Nobel Prize for his part in discovering C60
In scientific correspondence to the journal Nature, they describe how they made closed-cage octahedra by firing a laser at a target of MoS2.

"We think that the octahedron is the preferred geometry of MoS2 and we formed them in two sizes with the larger size having three MoS2 layers and the smaller size having two MoS2 layers," NREL researcher Dr Mike Heben told BBC News Online. "They are approximately 30 to 40 angstroms in cross-section.


Mike Heben says inorganic fullerenes should have a wide range of applications
"There may be a family of these that extend to larger sizes, much like Russian dolls."

Future applications

The desire of MoS2 to make cages of preferred sizes and of a preferred shape suggests the structures may display fullerene-type properties.

If this is correct, and it can be shown for other inorganic materials as well, scientists could greatly extend the range of applications for fullerenes.

"We want to make bulk quantities of this octahedron. We want to make enough of them so that we can begin to probe their interesting properties," Dr Heben said. "We think they may be useful in photocatalysis, perhaps in electricity generation some day, magnetic memory and in lubricants."

The NREL team includes Philip A. Parilla, Anne C. Dillon, Kim M. Jones, Gerald Riker, Douglas L. Schulz, David S. Ginley and Michael J. Heben.



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