Texas Tech University chemist Louisa Hope-Weeks and her research group wanted to make an optically active explosive material. Such a material could be used, for example, by a bomb squad to blow up a car that they suspect contains a terrorist device. The squad could remotely put the explosive under the car and then activate it from a safe distance with a laser.
The Hope-Weeks group has not made any optically active materials yet. But “by making and solving the x-ray crystal structures of three materials based on metal hydrazine polymers, the team can relate the materials’ properties to their structures,” reports Philip Broadwith in Chemistry World. In addition, the research could help eliminate the need for toxic heavy metals in explosives.
Thomas Klapötke, an energetic materials expert from the University of Munich in Germany, told Chemistry World that crystallizing and characterizing these materials was “impressive” because the polymers are hard to crystallize. Ionic polymers are interesting, he noted, because they are nontoxic and not hydroscopic. Because they do not react with water, the materials have a more stable and longer shelf life than other materials.
Explosives research is dangerous, and Broadwith notes that the compounds caused a serious explosion in the Hopes-Weeks lab in 2010. A lab member was seriously injured. Hope-Weeks told Chemistry World that she has changed the way she managed her lab. She cut the nickel hydrazine perchlorate crystal that was used for the characterization. No special equipment was used, she told Broadwith, because the crystal was small enough that it was unlikely to do significant damage to the instrument if it exploded.
Broadwith notes that the characterization should help Hope-Weeks and her group to understand as well as tune and refine the stability and energetic properties of similar compounds. He explains:
For example, in nickel hydrazine nitrate — which is already used as a primary explosive, but whose crystal structure was unknown — each metal atom is linked to the next by three bridging hydrazine ligands. However, in nickel hydrazine perchlorate, only one hydrazine bridges between metal centres, with four more hydrazines coordinated to each nickel. This means the whole polymer is less strongly held together, making it significantly more sensitive. And when it does explode it can release more energy, because of the potential to produce more nitrogen gas per metal atom and form more thermodynamically stable products like nickel chloride rather than nickel metal. Changing the metal to cobalt produced a material with the same structure, but that was significantly less sensitive.
Source: “Ionic polymers open door to greener, safer explosives,” Chemistry World, 1/13/12
Image from Wikimedia Commons, under Fair Use: Reporting.
Rachel Petkewich is a freelance science writer and editor. She has worked as a research scientist in the chemical industry and spent eight years as a staff writer and editor at various science journals and magazines, including Chemical & Engineering News.