Pentazenium tetraazidoborate is an extremely unstable chemical compound with the formula N5[B(N3)4].

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%),[1] being surpassed only by hydrazoic acid (97.7%).

The production of N5[B(N3)4] requires a multi-step synthesis, first, hydrazoic acid and sodium borohydride is reacted in diethyl ether at -78 °C to produce sodium tetraazidoborate (which decomposes at 76 °C):[2] The other reactant, pentazenium hexafluoroantimonate, its produced by the reaction of N2F+ and antimony(V) fluoride.

The overall reaction is the following:[3] The compound is extremely sensitive, an attempted Raman spectroscopy of a 500 mg sample of the compound resulted in an explosion.