In this project, funded by the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, Alan L. Balch and Marilyn M. Olmstead of the University of California, Davis will explore the structures and chemical reactivity of a promising group of endohedral fullerenes, cages of carbon atoms that encapsulate a variety of atoms, ions or small molecules. Work on the structural characterization of large fullerene cages and chiral fullerene cages by X-ray diffraction involves molecules that provide a bridge between smaller, nearly spherical fullerenes like the Bucky ball, C60, and carbon nanotubes. The use of endohedral fullerenes in light harvesting and other electro-optical and electrochemical devices involves reduction and oxidation of these molecules, yet little is known about the structures and chemical reactivities of externally functionalized endohedral fullerenes and of the cations and anions formed by oxidation and reduction of these endohedral fullerenes. The researchers intend to prepare crystalline salts of a variety of endohedral fullerenes to determine how oxidation and reduction behavior alters their structure, the location of the contents with regard to the cage, and the nature of interactions between atoms inside cages. They have discovered several new families of fullerenes with compositions M3C106-124, M4C122-154, M3C107-125 and will explore the chemical reactivity and structures of these remarkable molecules.
This project will provide state of the art laboratory experiences for graduate and undergraduate students who will be learning the techniques of chemical synthesis, fullerene formation in an electric arc, chromatographic methods of fullerene separation and purification, crystal and cocrystal growth, and single crystal X-ray diffraction methods including both conventional in-house sources and synchrotron radiation. The students will also learn how to collaborate within the group and also with scientists in varied locations globally. Once a rare chemical, the prototypical fullerene, C60, is now available in ton quantities. Professors Balch and Olmstead anticipate a similar increase in the availability of endohedral fullerenes. Endohedral fullerenes are versatile materials that have properties that reflect the nature of the atoms trapped inside. Thus, gadolinium-containing endohedrals are effective contrast agents for magnetic resonance imaging and have the advantage of safely trapping the toxic gadolinium atoms inside an unreactive carbon cage. Lutetium-containing endohedrals are useful in X-ray contrast imaging. Fullerenes are the molecules of choice in the design of new plastic solar cells, and endohedral fullerenes represent a promising new set of molecules to improve and enhance the operational characteristics of these cells.
