Fullerene Traps Longest Metal Bond

By trapping two terbium atoms within a C₇₉N fullerene cage, chemists have created the longest metal-metal bond measured to date (J. Am. Chem. Soc., DOI: 10.1021/ja802417d). The terbium atoms share a single-electron bond a tad more than 3.9-?? long. A research team led by Alan L. Balch of the University of California, Davis, and Harry C. Dorn of Virginia Polytechnic Institute & State University prepared and characterized the endohedral fullerene, as well as an analog that holds a pair of yttrium atoms. To create the compounds, the researchers employed the Krätschmer-Huffman electric-arc process to vaporize graphite rods doped with either Tb₄O₇ or Y₂O₃. They then purified enough material for crystallographic and spectroscopic studies. Computational analyses of the yttrium analog indicate that the compound is a very stable radical in which the metal atoms share an unpaired electron in their bonding orbital. According to Dorn, these molecules represent a new class of metalloheterofullerenes. Such compounds could find practical applications as contrast agents for magnetic resonance imaging or could be used in new spintronic and semiconductor applications.