The Pnictogen Wing

azide ion, N₃^-, ^-N=N⁺=N^-, is one of the most fascinating of inorganic ions to me. among its intriguing properties:

1. it's quite poisonous, for it bonds to the central iron atom of heme much as does cyanide and carbon monoxide. but this makes sodium azide a very useful preservative: a smidge of NaN₃ added to laboratory solutions that might be otherwise inclined to rot (e.g. phosphate buffer solutions) keeps them fresh during prolonged storage.

2. it's explosive. I mean, just look at it—it looks like it wants to decompose to molecular nitrogen and that's exactly what it does, especially in heavy-metal salts like silver azide and lead(2) azide, which lead to the extensive use of azides in detonators and percussion caps. NaN₃ is fairly stable but can still be induced to detonate; as such, it was used in automotive airbags and other devices designed to inflate rapidly in an emergency, but I believe it's being outmoded.

3. it's a "pseudohalide", an ion that behaves much like a halide in chemical compounds. hydrogen azide is somewhat like hydrogen chloride or hydrogen bromide—it's volatile and easily distilled (although, unlike HCl or HBr, HN₃ has a strong tendency to explode.) N₃^- is a good ligand in metal complexes, e.g. hexaäzidoferrate(3) or Fe(N₃)₆^≡, which is blood-red in color—rather like the related hexathiocyanato complex of Fe(3), Fe(SCN)₆^≡.

4. organic azides exist, analogous to organic halides; e.g. azidobenzene or phenyl azide, C₆H₅N₃ in analogy to chlorobenzene. like inorganic azides, organic azides are liable to blow up on rough handling. but they're useful chemical intermediates with fascinating chemistry, like 1,3-dipolar cycloadditions across multiple bonds to yield five-membered heterocycles (q.v. the Huisgen "click chemistry" cycloaddition: https://en.wikipedia.org/wiki/Azide-alkyne_Huisgen_cycloaddition).

I'd love to have some sodium azide on hand but synthesis of azide salts is somewhat tricky. the usual cited laboratory method involves reaction of a nitrite ester (e.g. isopropyl nitrite) with hydrazine in alkaline solution, which can't quite be called a simple method.

~Chara