Number 65 (Story #3), January 24, 1992 by Phillip F. Schewe and Ben Stein|
STRUCTURALLY DISTINCT COUSINS OF FULLERENES have been hypothesized by two research teams working independently. The proposed structures, C-168 "buckygyms" (a Rutgers-IBM team) and C-216 "schwarzite" (a Cornell-Corning team), would form from flat graphite sheets, as is the case with fullerenes, but the sheets would contain 7-atom carbon rings instead of 5-atom rings. Whereas the presence of the 5-fold rings in the growing graphitic sheet causes it to curl "positively" into the closed spheres we know as Buckyballs, the 7-fold carbon rings would cause the proposed clusters to fold "negatively," contorting locally into saddlelike shapes and forming an infinite cagelike structure (the large-scale structure of C-168 would be similar to diamond, but with a unit cell 100 times bigger). The C-168 researchers predict that the material would have elastic constants similar to those of silicon but with half the density of graphite, making for a lightweight, durable structure. The C-216 designers predict that their structure would be more energy efficient than fullerenes; the C-168 researchers make the same prediction. No one has found these structures, but the C-216 researchers say that they may already be made with fullerenes in conventional carbon-arc setups. (C-168: Vanderbilt et al., 27 Jan. Physical Review Letters; contact Jerry Tersoff of IBM, 914-945-3138; C-216: Lenosky et al., 23 Jan. 1992 issue of Nature).