NEWS OF THE WEEK MATERIALS
SCIENCE
POLYNITROGEN Single-bonded nitrogen allotrope, if harnessed, could serve as a propellant NATURE © 2004
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CIENTISTS HAVE EAGERLY
studied the behavior of molecular nitrogen under high pressure for nearly 2 0 years, searching for evidence of polymeric nitrogen, a single-bonded form of nitrogen with a structure similar to that of diamond. Several new nitrogen phases have been discovered, including a nonmolecular semiconducting phase, but polymeric nitrogen has remained elusive. Until now In the August issue of Nature Materials (http://dx.doi.org/10. 1038/nmatll46), Mikhail I. Eremets of Max Planck Institute for Chemistry, in Mainz, Germany, and coworkers report the prepa-
UNDER PRESSURE Single-bonded polymeric phase of nitrogen has a diamond-like structure.
CHEMISTRY
ration of polynitrogen by compressing N 2 above 110 gigapascals (about 1.1 million atm) and 2,000 Kin a tiny laser-heated diamond anvil cell. Raman scattering and X-ray data indicate that each nitrogen atom in the product is connected to three neighbors by single covalent bonds. The material is stable at room temperature at pressures above 42 GPa, though the researchers were unable to isolate an intact sample at atmospheric pressure. They hope to devise a method to isolate polynitrogen, but doing so might require stabilizing it in the form of compounds containing other elements or by in-
CONTEST
CHINA SHINES AT OLYMPIAD U.S. team receives four silver medals; Russian student earns highest overall SILVER MEDALISTS The U.S. Chemistry Olympiad team: from left, Brown, Zhang, Tsui, and Kiappes.
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HINA CONTINUED ITS DOM-
inant performance at the 36 th International Chemistry Olympiad, which t o o k place from July 18 to 27 in Kiel, Germany. Once again, it was
2004
the only team to earn four gold medals. South Korea also placed well, receiving three gold medals and one silver. Home team Germany took two golds and two silvers, while Poland and Hungary each earned two golds, one silver, and one bronze. All four members of the U.S. team won silver medals. This year, high school students from more than 60 countries participated in the annual chemistry competition, which featured fivehour practical and theoretical exams. The practical exam included an organic synthesis and a compound analysis, and the theoreti-
troducing impurities, they note. Nitrogen is unique in that the triple bond holding the diatomic molecule together is one of the most stable chemical bonds known, notes chemistry professor Thomas M. Klapotke of Ludwig Maximilians University inMunich, Germany In contrast, polymeric nitrogen is expected to be highly unstable because the N - N single bond is relatively weak (160 kj per mole). Decomposition to N 2 and formation of the much stronger triple bond (954 kj per mole) would be highly exothermic. Polynitrogen should have an energy capacity more than five times that of the most powerful nonnuclear energetic materials and "would seem to be the ideal high-energy-density material," Klapotke says. Further experiments are needed to determine whether polynitrogen could ever be suitable as a propellant or, less likely as an explosive, he adds. -STEPHEN RITTER
cal exam consisted of eight fivepart questions covering kinetics, thermodynamics, stereochemistry and other topics. The Russian Federation's Alexey Zelfinan obtained the highest total score. Students also took sightseeing trips, toured chemistry facilities, and made sailing excursions as part of the Olympiad's official program. The U.S. team—Eric Brown, John L. Kiappes Jr., Emily Tsui, and Fan Zhang—was accompanied by coaches Nadine Szczepanski of MacMurray College, Jacksonville, 111., and Todd Trout of Lancaster Country Day School, Lancaster, Pa. The students were selected at the end of a two-week study camp held in June. Brown and Tsui both plan on starting college at Massachusetts Institute of Technology this fall, and Kiappes will attend Rice University. Zhang will return to Bergen CountyAcademies, Hackensack, N.J., for his senior year. —AAL0KMEHTA
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