Inorg. Chem. 52, 13791–13802 (2013)

Credit: © 2013 ACS

Primary explosives are high-energy materials that are typically used in small amounts to trigger the detonation of larger quantities of more stable explosives that are easier to store and handle. Not only is accidental detonation of these highly sensitive materials a major concern, but toxicity can also be a problem, such as in the case of the commonly used lead azide. In an effort to improve the safety of these primary explosives, researchers are making and studying a range of different high-energy metal–ligand complexes that are non-toxic and that can potentially be detonated in a more controlled fashion, such as with a short laser pulse.

Now, Thomas Klapötke and co-workers at the University of Munich have prepared and investigated the properties of a series of metal complexes incorporating nitrogen-rich 3-amino-1-nitroguanidine (ANQ) ligands. Starting from a selection of simple Co, Ni, Cu, Zn and Ag salts, a range of different metal–ANQ complexes were formed, with either chloride, nitrate or perchlorate anions. In the case of Co, Ni and Ag, ANQ complexes with dinitramide anions, (NO2)2N, were also prepared. In total, 17 different compounds were isolated and all of their solid-state structures were characterized using single-crystal X-ray analysis. Tests revealed that the materials displayed a range of impact and friction sensitivities with, on average, the perchlorate salts being the most sensitive and, perhaps unsurprisingly, the chloride salts being the least sensitive (chloride is a non-energetic anion).

Some of the perchlorate, nitrate and dinitramide complexes underwent laser ignition tests in which small pressed pellets of the samples were exposed to a single 100-μs pulse of a 940-nm-wavelength laser. Only the Co, Cu and Ag perchlorate complexes detonated under these conditions, with none of the nitrate or dinitramide materials showing any response to the laser pulse. Although the mechanism by which the laser irradiation causes these metal complexes to detonate is not known, this study does offer some clues and points to an electronic process rather than a thermal trigger.