Sep. 3, 1999 BLACKSBURG, Aug. 30, 1999 -- Leaky lab equipment and Virginia Tech researchers' eagle eyes have resulted in a new family of molecules with potential applications ranging from medicine to optical-electronic devices, and beyond. The researchers report in the Sept. 2, 1999, issue of Nature that they can produce C80 fullerenes containing three metal atoms ("Small-bandgap endohedral metallofullerenes in high yield and purity").
Researchers worldwide, who have been experimenting with the new form of carbon atoms called fullerenes, have been mystified for about five years by a small peak in their mass spectrometry readouts, called 1109 because that is its mass.
Discovered in 1985 and named after Buckminster Fuller, designer of the geodesic dome, fullerenes are clusters of carbon with an even number of atoms forming a ball-shaped cage. Since determining that clusters with even numbers of atoms, in particular in the range of 60 to 80 atoms (C60 etc.), form a stable molecular structure, scientists have been trying to insert metals into the cages and to produce the structures in useful quantities. There has been some success in getting fullerenes to carry one or two metal atoms – but not with ease or in high quantity.
Now, however, the Virginia Tech researchers report they can produce metallofullerenes cheaply and with high yield.
Lead researcher Harry Dorn, Virginia Tech professor of chemistry, and Steve Stevenson, post doctoral fellow at Tech, have also applied for a patent for their inexpensive, high-yield process and for the new family of molecules.
"Not only is it unique and beautiful," says Dorn, "It has many potential applications, depending upon the metals and metal mixtures inserted." Insert magnetic material and there are semiconductor and, perhaps, superconductor applications. Insert other metals for fluorescent and other optical properties and to amplify fiber optic applications. Insert radioactive material and use the molecule as a tracer in medical applications, with the carbon cage protecting the radioactive center. Fluorescent and optical tags can also be used as tracers for medical and other applications. The carbon cage can also protect materials used as contrast agents in MRI procedures. Quantum computing devices can be created by including atoms that have unpaired electrons and/or spin active materials.
Even when destroyed, the molecule is useful. "It doesn't decompose until heated to 400 degrees centigrade," says Dorn. "Then it turns from black to white as the carbon burns off, leaving metal oxide particles with different properties than the original metals. This is a new way to prepare metal oxide, such as for protective surfaces or as a catalyst when materials are bonded," says Dorn.
The cages can also be formed into tubes or "nano-pencils" to record and store data or draw lines that could only be seen with powerful electronic scanning microscopes. "Not only wouldn't you be able to see the lines, you wouldn't be able to see the pencil," says Stevenson. Dorn points out that in addition to being able to record a lot of data in a small area, the tubes could draw conductive lines on tiny chips for a host of modern applications.
About that mysterious readout
The discovery of the stable metallofullerene is a result of tracking down a small, unexplained peak in the data that accompanied virtually every analysis of fullerenes the Virginia Tech team created.
Dorn first reported 1109 in a paper in 1994 – reported it in passing in the discussion of his fullerene research. "The level would vary in different mixtures as we produced different fullerenes." The researchers would drill holes in graphite rods, insert metals, place them in a sealed chamber, then burn the rods with an electric arc generator, forming carbon atom cages around the metal of choice.
"The appearance of 1109 was consistent and we decided to find out what it was," recalls Dorn. "Steve and I took reams of data – NMR readouts, mass spec readouts, XPS (X-ray photo-electron spectroscopy) data – and went to (one of the food courts on campus). We spent two or three hours pouring over it. After about the fourth cup of coffee, we had it narrowed down to the most likely material."
Stevenson recalls, "He asked me, 'What's the second choice?' and I said, 'There isn't any.'"
The mystery material was nitrogen.
"Then everything made sense," says Dorn.
The equipment was letting atmospheric nitrogen into the chamber. "The arc disassociated it into nitride atoms. The metals latched onto the nitride – three atoms of metals onto one atom of nitride – and as it cooled, the carbon cage formed. So you have a molecule with a non-metal core, the three metals, then the non-metal cage.
The researchers were working with erbium because they were receiving funding from Fiber & Sensor Technologies Inc., which saw the potential for fullerenes containing that metal in optical amplifiers and optical-electronic devices. Dorn and his team of students and staff were also working with scandium because it is well known that it will go into the carbon cage and it is easily tracked with NMR.
It is the first example of isolated four atom molecular clusters in a fullerene cage, and the first example of such a cluster with a nitrogen atom at the center, Dorn reports. "It looks like a whirling Mercedes Benz emblame inside a ball," he says.
The researchers had their coffee-induced epiphany in November 1998. They fine-tuned and confirmed their findings, created materials on purpose, and reported their discoveries to Nature in December. The magazine editors asked for confirmation from external sources of the molecule's content and that it was an endohedral structure. The material was sent to several labs. Subsequently, Roy Bible and colleagues at Searle provided the NMR confirmation of content, and Alan Balch, Marilyn Olmstead, and chemistry department colleagues at the University of California at Davis confirmed the crystal structure.
"It's interesting that several other labs around the world have had 1109 and didn’t know it. A group in Japan misidentified it. It was talked about at conferences for three or four years. No one else realized what they really had," says Dorn.
Dorn and Stevenson remember the day and the hour they made the discovery, and can take you to the table in the Johnson Student Center.
Co-authors on the Nature article, in order listed, are, from Virginia Tech: Stevenson;, Greg Rice, undergraduate student in computer science who was running the experiments when the leaks occurred; Tom Glass, NMR technician; Kim Harich, mass spectrometry technician; Frank Cromer, XPS technician; M.R. Jordan, postdoctoral student; and Jennifer Craft, undergraduate student in chemistry who did the XPS and decomposition study; from Searle: Elizabeth Hadju and Roy Bible; from U.C. Davis: Olmstead, K. Maltra, A.J. Fischer, and Balch; and Dorn from Virginia Tech.
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