Polyazides are highly endothermic compounds that have great potential as energetic materials. For example, lead diazide is widely used as primary explosive. The low toxicity and environmentally benign character of bismuth renders it an ideal replacement for lead in this application. As a consequence, we have systematically studied the synthesis and characterization of binary bismuth and related group 15 polyazides.The binary group 15 polyazides, As(N3)3, Sb(N3)3 and Bi(N3)3 were prepared and stabilized by either anion or donor-acceptor adduct formation. Crystal structures are reported for [Bi(N3)4]-, [Bi(N3)5]2-, [bipyBi(N3)5]2-, [Bi(N3)6]3-, bipyAs(N3)3, bipySb(N3)3 and [(bipy)2Bi(N3)3]2. An interesting feature of these pnicogen(+III) compounds is the presence of a free valence electron pair on the central atom. The [Bi(N3)5]2- anion possesses a sterically active, free, Bi valence electron pair and a monomeric, pseudo-octahedral structure with CN 6, while its bipyridyl adduct has a pseudo-monocapped trigonal prismatic structure with CN 7 and a sterically inactive free valence electron pair. Attempts to grow single crystals of polymeric, free Bi(N3)3 were unsuccessful. However, the crystal structure of its bis-bipyridyl adduct, [(bipy)2Bi(N3)3]2, was successfully determined. It is dimeric and made up from two square BiN8 antiprisms, with Bi having CN 8 and a sterically inactive, free valence electron pair, and sharing an edge consisting of two �1,1-bridging N3 ligands.  The novel bipyAs(N3)3 and bipySb(N3)3 adducts were also prepared and structurally characterized. They are monomeric, isostructural and contain a sterically active, free valence electron pair on their central atom and a coordination number of 6.

Green energetic materials: Binary group 15 polyazides

243rd National Meeting (2012)

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