SCIENCE & TECHNOLOGY
CHOCK FULL OF NITROGEN New syntheses could lead to a solid all-nitrogen compound that's stable under ambient conditions
the azobis(diazidotriazine) in three steps from a hydrazobis(dichlorotriazine). Traditional polynitro compounds, such as trinitrotoluene (TNT), derive their explosive power from combustion of the carbon backbone of the molecule using the oxygen carried by the nitro groups, they note. Newer polynitro compounds gain additional power by having higher nitrogen content coupled with the strain of small rings or cage structures. The latest nitrogen-rich compounds —tetrazines and triazines—can unleash even greater force with their large number of N - N bonds, Fliskey and coworkers add. As a bonus, these compounds primarily form N 2 on detonation, an environmentally friendlier by-product than those from traditional HEDMs.
SOLID A L L - N I T R O G E N COMstable" AsF 6 " salt in 1999. Christe and pound at room temperature coworkers later made the more stable and pressure?That's an intriguSbF6~ salt and have tried to make the alling thought. Even better would nitrogen compound N5+N3~. But even the be an all-nitrogen compound usually stable azide anion (N3~) has not althat's stable enough to be handled and lowed their attempts to end in anything processed into useful materials. The possiother than explosions. They also have idenbility that such a compound might be made tified the cyclic N5~ anion in the gas phase, is getting closer to fruition, as evidenced by which opened another avenue to explore, several papers in the Sept. 20 issue ofAngeincluding the possibility of preparing wandte Chemie International Edition. N 5 + N 5 ". Yet, the researchers are giving up on trying to make these all-nitrogen comOn page 4919 of that issue, Ralf Haiges, pounds because theoretical calculations FOR COMPARISON, T N T has a heat of Karl O. Christe, and coworkers at the Uniindicate that they simply are too unstable formation o f - 6 4 kj per mol, whereas versity of Southern California report the to isolate as solids. 2,4,6 -tri(azido)-l,3,5-triazine (cyanuric preparation and spectroscopic characterazide) has a positive heat of formation of ization of new pentanitrogen cation salts, Haiges and Christe report that they 1,053 kj per mol. Huynh and Hiskey's triincluding N 5 + P(N 3 ) 6 -and N 5 + B(N 3 ) 4 -. On have come pretty close to an all-nitrogen azine compound far surpasses that level at page 4 9 2 4 , My-Hang V. Huynh and molecule anyway with their latest N5+ salts. 2,171 kj per mol. Its energy density of 6.17 Michael A. Hiskey of Los Alamos National The extremely shock-sensitive N S P(N 3 ) 6 kj per g is close to the value of 6.84 kj per Laboratory and coworkers report the synand N 5 B(N 3 ) 4 were prepared bv reacting g estimated for N 5 P(N 3 ) 6 . thesis and full characterization of an azoN 5 SbF 6 with NaP(N 3 ) 6 or NaB(N 3 ) 4 in liqbis(diazidotriazine) (C 6 N 20 ). And on page uid S 0 2 at - 6 4 °C. The boron compound, Knapp and Passmore's commentary sum4834, Carsten Knapp and Jack Passmore with a molecular formula of BN17, sets a marizes recent work on tellurium and othof the University of New Brunswick, Frednew record for the most nitrogen content er polyazido compounds synthesized by ericton, provide a commentary on the in a solid: 957 weight %, Christe says. Christe's group and a group led by Thomas progress being made in the synthesis of Hiskey and his collaborators have been M. Klapotke of the University of Munich, high-nitrogen-content compounds and taking a different approach for preparing in Germany Last year, both groups indehint at the possibility of "solid nitrogen." HEDMs. For several years, the Los Alapendently reported the synthesis ofIe(N 3 ) 4 as well as compounds containing Several solid nitrogen-rich comTe(N3)5~, and Christe's group made a pounds reported in the past fewyears LOTTA NITROGEN have come remarkably close to 100% Te(N3)62 compound. Also, earlier this Nitrogen-rich compounds up the ante on nitrogen, in some cases being only one year Christe's group reported the analpreparing stable high-energy-density materials atom away These compounds, beogous titanium polyazides. Passmore's sides being an interesting gambit to group carried out some of the early N=N—N N—N = N gain fundamental chemical knowlwork on the tellurium azides in the edge, are potential candidates as com>)— N = N — ( ' late 1980s. The sulfur and selenium mercial high-energy-density materials homologs are still unknown, Knapp (HEDMs) used as explosives, proN = N—N N —N=N and Passmore point out. CM, pellants, and fireworks. Klapotke's group has prepared and Earlier this year, a single-bonded studied a number of HEDMs, innitrogen allotrope, called polymercluding many main-group azides in N = N—N N —N=N /N\ \ D ^ ic nitrogen, was made by compressaddition to the tellurium compounds. • N = N—N" ^N — N = N ing N 2 above 110 gigapascals (about Christe's N s + phosphorus and boron 1.1 million atm) and 2 , 0 0 0 K azido salts maybe too sensitive to be BN 1 7 (C&EN, Aug. 2, page 10). This all-niused as HEDMs, Klapotke notes. trogen compound has a diamondBut the triazine made by Hiskey's like structure and is stable at room temgroup "may well be of interest as an HEDM mos researchers have been synthesizing a perature at pressures above 42 GPa, but it in suitable formulations," he adds. variety of compounds containing tetrazine doesn't seem likely that it can be isolated (C 2 N 4 ) rings with nitrogen substituent "These developments show that some of at ambient pressure without stabilizing it groups. A natural extension of the work the most outrageous compounds imaginable with other elements. Thus, preparing highhas been to make the azotriazines, Fliskey can be prepared and characterized," Knapp nitrogen-content compounds by tradisays, and the team realized that azido-suband Passmore conclude. They believe many tional synthetic chemistry appears to still stituted azobis(triazines) would have a very other simple species with even greater nihave the inside track. high positive heat of formation, giving trogen content will be isolated and characthem great explosive power. Huynh, terized in the next fewyears—perhaps even Christe's group first prepared the N 5 + Hiskey, and coworkers then synthesized an all-nitrogen compound.—STEVERITTER cation and isolated it as the "marginally
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