Selenium Nitride, Se₄N₄

Selenium Nitride, Se₄N₄ was first obtained in 1859 by saturating selenium tetrachloride with ammonia in the cold:

12SeCl₄ + 64NH₃ = 3Se₄N₄ + 48NH₄Cl + 2N₂.

It may also be prepared by passing a stream of dry ammonia into a 2 to 4 per cent, solution of selenyl chloride in benzene. The nitride is precipitated as a buff-coloured solid which becomes orange-red when dry. Some free selenium is deposited along with the nitride, the amount increasing with the concentration of the selenyl chloride solution. After washing the buff precipitate the free selenium may be extracted by means of potassium cyanide solution.

By each of these methods the nitride is obtained as a brick-red amorphous powder which, when dry, is highly explosive, detonating violently on slight touch, forming a cloud of red selenium; it is considerably more sensitive than mercury fulminate.

After investigating the action of liquid ammonia on a variety of selenium compounds, Strecker and Claus have come to the conclusion that the tetrahalides are the best initial materials for the preparation of selenium nitride. The action of liquid ammonia on selenium tetrabromide in the presence of carbon disulphide gives a good yield of the nitride.

Selenium nitride is insoluble in water, alcohol and ether, slightly soluble in carbon disulphide, benzene and glacial acetic acid. It is decomposed by caustic potash with the formation of potassium selenite, ammonia and free selenium. It reacts explosively with both chlorine and bromine. In the presence of carbon disulphide the action of bromine leads to the formation of a brownish-green hygroscopic substance having the composition SeN₂Br₄. If the bromine vapour is diluted with carbon dioxide, the nitride is converted into ammonium selenibromide, (NH₄)₂SeBr₆, the formation of which appears to be due to the action of atmospheric moisture on a primary addition product. In similar circumstances chlorine yields a compound of composition SeNCl₃. Iodine, whether solid or dissolved in ether or chloroform, has no action on selenium nitride.

A suitable solvent is not available for the determination of the molecular weight of the nitride, but evidence seems to favour a cyclic structure for the molecule Se₄N₄.