NEWS OF THE WEEK
BUCKMINSTERrULLERENE: C 60 continues to amaze chemists Chemists around the world were surprised last year when two physicists published a sim ple method for producing mac roscopic amounts of buckminsterfullerene, the 60-carbon atom molecule with the geom etry of a soccer ball. As chem ists have studied C 60 and the family of carbon-cage mole cules that have become known as fullerenes, surprise has giv en way to glee as one remark able property after another has been revealed. The parade of fascinating re sults continued last week. One research group announced that C 60 doped with tetrakis(dimethylamino)ethylene (TDAE) becomes an organic molecular Wudl: discovered "soft" C60 ferromagnet ferromagnet at 16.1 K. Another group announced that C 60 doped ing agent, might substitute for the with cesium and rubidium is a su alkali metal in donating electrons to perconductor at 33 K. Still another C 60 to form an organic, molecular group produced cesium-doped C 60 superconductor. and found it is a superconductor at Instead, they discovered C 60 30 K. And a theorist calculated that (TDAE)0 86 exhibits properties of a fully reduced buckminsterfullerene, "soft" ferromagnet below 16.1 K. C 60 H 60 , which he calls buckminster- That is, the material becomes mag fullerane, would be most stable netized in a magnetic field but loses when 10 of the hydrogens are on its magnetization when the magnet the inside of the cage. ic field is removed. Previous nonC 60 doped with TDAE was pro polymeric organic compounds that duced and characterized by Fred exhibited ferromagnetism did so Wudl, a chemistry professor at the only at 1 to 2 K. University of California, Santa Bar Because it is not a permanent fer bara; Pierre-Marc Allemand, a post romagnet, TDAE-doped C 60 is un doctoral fellow; and coworkers likely to have any practical uses, working in collaboration with scien Wudl says. However, he adds, "Over tists at the University of California, the last 20 years, organic chemists Los Angeles, and Los Alamos Na have successfully sought to make tional Laboratory [Science, 253, 301 substances that imitate inorganic ma (1991)]. Earlier research at AT&T terials in areas like semiconductors Bell Laboratories and at UCLA had and superconductors. The last fron demonstrated that C 60 doped with tier is ferromagnetism. Apparently, potassium or rubidium supercon- we have broken that frontier with ducts at 18 Κ and 29 K, respectively. C60." Wudl believes further tinkering Wudl and his collaborators reasoned will lead to a permanent organic fer that TDAE, which is a strong reduc- romagnet based on C60. 4
July 22, 1991 C&EN
At the Fundamental Research Laboratories of NEC Corp., Tsukuba, Japan, Thomas E. Ebbesen and coworkers doped C 60 by exposing it to rubidium and cesium vapor [Nature, 352, 222 (1991)]. The UCLA researchers who demonstrated that RbxC60 is a superconductor also pre pared Cs-doped C 60 , but the material was not superconduct ing. However, according to the NEC scientists, there are theo retical reasons to suspect that doping C 60 with larger alkali metal atoms like cesium will produce a material with a high er superconducting transition temperature (Tc) than potassi um- or rubidium-doped C60. So Ebbesen and coworkers turned to doping C 60 with vari ous proportions of cesium and the smaller alkali metal atom, rubidium. They produce a material, CsxRbyC60 (with χ = 2 and y = 1 based on the amount of cesium and rubidium to which C 60 was exposed), with a Tc of 33 K. More than 60% of the material is superconducting, they report. The high Tc, which is exceeded only by the copper oxide superconductors, and the high proportion of the mate rial that is superconducting suggest that mixing dopants may be a prom ising strategy for achieving optimal superconducting properties in doped C60. Interestingly, the NEC research ers also failed to produce a supercon ductor when they doped C 60 with pure cesium. However, at Harvard University, chemistry professor Charles M. Lieber and coworkers have produced cesium-doped C 60 that is supercon ducting. Most of the research on al kali metal-doped C 60 superconduc tors involved material that had been produced by simply exposing the fullerene to an alkali metal vapor.
For potassium, this strategy allows preparation of the superconducting phase, K3C60, without proceeding to the nonsuperconducting phase, K6C60, and the same presumably holds true for rubidium. But the Harvard researchers used a different synthetic strategy. To achieve greater control of the doping process, Lieber and coworkers worked with binary alloys of cesium— CsHgx !, CsTl2, or CsBi— which are less reactive than pure cesium metal [Nature, 352, 223 (1991)]. According to Lieber, previous research has demonstrated that alkali metal-M (M = Hg, Tl, or Bi) intercalation of graphite produced ternary complexes with both the alkali metal and metal atoms forming a complex with graphite. That doesn't appear to occur with C60, however. Instead, reaction of C60 with each of the three cesium alloys results in production of superconducting compounds with Tcs of about 30 K. Since nearly the same Tc is observed for all three compounds, the Harvard chemists conclude that an identical superconducting phase is formed in all three reactions, which must correspond to CsxC60 (x = 1.2 to 3). The Harvard studies suggest the Cs-doped C60 superconductor is less stable than the potassium- or rubidium-doped C60 superconductors. At Yale University, chemistry professor Martin Saunders used a molecular mechanics program to investigate the stereoisomers of C60H60 [Science, 253, 330 (1991)]. Chemical reduction of C60 would likely deliver all of the hydrogens to the outside of the fullerene cage, Saunders points out, but such a structure would be highly strained. Saunders' calculations suggest that moving only one hydrogen to the inside of the fullerene cage would decrease the energy of the molecule by 53 kcal per mole. Putting additional hydrogens on the inside further lowers the predicted energy, with a minimum-energy isomer having 10 hydrogens on the inside. This molecule would have an energy 400 kcal per mole lower than that of the buckminsterfullerane isomer with all hydrogens on the outside, Saunders says. Rudy Baum
Earnings, sales up for pharmaceutical firms Double-digit improvements in earnings and, in most cases, sales were being reported by U.S. pharmaceutical companies last week as results for the year's second quarter started to come in. For instance, at Bristol-Myers Squibb, earnings increased 17% from last year's second quarter to $490 million, on a 10% sales gain to $2.73 billion. The company cites improved domestic sales, particularly strong sales of pharmaceutical and medical devices, as the cause for its strong showing. Upjohn was one of the few companies reporting sales growing at a faster rate than earnings. Earnings from continuing operations at the company rose 12% to $128 million, but sales grew 14% to $859 million. However, Upjohn had some nonrecurring items on its balance sheet for last year's second quarter; if these are excluded, the company says earnings increased 34%. Earnings for Marion Merrell Dow increased 25% to $162 million on a 14% sales gain to $718 million. One reason for the improvement, besides
higher product sales, is that the firm is becoming more aggressive in the Canadian marketplace, the company says. American Home Products showed only a slight sales improvement of 1% to $1.62 billion, but earnings from continuing operations were up 32% to $265 million. However, the company explains that the sales figure for last year's second quarter included $187 million from operations that were sold at the end of that threemonth period. If these are excluded, the company showed a 14% increase in sales from continuing operations. Another company whose divested businesses made a difference was Schering-Plough. Sales were up just 6% to $913 million, and earnings rose 16% to $167 million. However, the company says, sales growth in the second quarter was reduced by the absence of sales from the Maybelline cosmetics business that was divested in July 1990. Excluding the impact of the divestiture, Schering-Plough's consolidated sales would have increased 14% in the second quarter. William Storck
Wary response to UJS. chemical arms proposal The U.S. and three allies have offered a new chemical weapons verification proposal to the ongoing Conference on Disarmament in Geneva. This proposal is more to the liking of military and intelligence establishments than the U.S.' previous one, but has scant support among continental European allies and may not be acceptable to Third World nations. This challenge inspection proposal, tabled last week, is a key element of a future chemical weapons treaty. Administration officials say it offers on-site challenge inspections, without delay, of any site in another nation party to the treaty to resolve compliance concerns. A challenged country cannot decline an inspection but can choose how the inspection will be carried out. "We think [the proposal] will be a very important boost to the negotiations," says Ronald F. Lehman, director of the U.S. Arms Control & Disarmament Agency. It may keep
the talks moving, but it has little general support. Only the U.K., Japan, and Australia reluctantly cosponsored the plan. No Europeans signed on, and neither did Canada, which usually is a staunch U.S. ally. According to one diplomatic observer, the nations that did cosponsor the proposal were resigned to the fact they wouldn't get anything better out of the U.S. and felt it was important to move the negotiations forward. In 1984 then-Vice President Bush tabled a U.S. proposal calling for anytime, anywhere challenge inspections without right of refusal. When, in 1987, the Soviets endorsed this concept, members of the U.S. military and intelligence establishment concerned about protecting ultrasecret "black" projects began lobbying for changes in the U.S. proposal. In August 1990 the U.S. floated a proposal within the socalled Western group of the disarJuly 22, 1991 C&EN
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