Silver Azide - Structure and Chemistry

Structure and Chemistry

Silver azide can be prepared by treating an aqueous solution of silver nitrate with sodium azide. The silver azide precipitates as a white solid, leaving sodium nitrate in solution.

AgNO₃ (aq) + NaN₃ (aq) → AgN₃ (s) + NaNO₃ (aq)

X-ray crystallography shows that AgN₃ is a coordination polymer with square planar Ag+ coordinated by four azide ligands. Correspondingly, each end of each azide ligand is connected to a pair of Ag+ centers. The structure consists of two-dimensional AgN₃ layers stacked one on top of the other, with weaker Ag–N bonds between layers. The coordination of Ag+ can alternatively be described as highly distorted 4 + 2 octahedral, the two more distant nitrogen atoms being part of the layers above and below.

In its most characteristic reaction, the solid decomposes explosively, releasing nitrogen gas:

2 AgN₃ (s) → 3 N₂ (g) + 2 Ag (s)

The first step in this decomposition is the production of free electrons and azide radicals; thus the reaction rate is increased by the addition of semiconducting oxides. Pure silver azide explodes at 340 °C, but the presence of impurities lowers this down to 270 °C. This reaction has a lower activation energy and initial delay than the corresponding decomposition of lead azide.