Pentazenium tetraazidoborate is an extremely unstable chemical compound with the formula N<sub>5</sub>[B(N<sub>3</sub>)<sub>4</sub>]. It is a white solid that violently explodes at room temperature. This compound has a 95.7% nitrogen content which is the second highest known of a chemical compound, exceeding even that of ammonium azide (93.3%) and 1-diazidocarbamoyl-5-azidotetrazole (89.1%), being surpassed only by hydrazoic acid (97.7%).
The production of N<sub>5</sub>[B(N<sub>3</sub>)<sub>4</sub>] requires a multi-step synthesis, first, hydrazoic acid and sodium borohydride is reacted in diethyl ether at -78 ðC to produce sodium tetraazidoborate (which decomposes at 76 ðC):
The other reactant, pentazenium hexafluoroantimonate, its produced by the reaction of N<sub>2</sub>F<sup>+</sup> and antimony(V) fluoride. Then, two reactants that are produced are mixed at -64 ðC under sulfur dioxide:
to produce the pentazenium tetraazidoborate. If heated, it decomposes into nitrogen gas and boron triazide; the boron triazide further decomposes into boron nitride and nitrogen. The overall reaction is the following:
The compound is extremely sensitive, an attempted Raman spectroscopy of a 500 mg sample of the compound resulted in an explosion.