Barium Cobalti-nitrite, Ba₃[Co(NO₂)₆]₂

Barium Cobalti-nitrite, Ba₃[Co(NO₂)₆]₂.14H₂O, is most conveniently obtained as a precipitate by addition of sodium cobalti-cyanide to one of barium chloride. It is yellow in colour, and not quite so stable as the alkali salts.

The corresponding double nitrites of caesium, rubidium, silver, and lead, have also been prepared as insoluble yellow precipitates. Rosenheim and Koppel attribute 12 molecules of water to the last-named, whilst Cunningham and Perkin find 4 molecules of water after the salt has been dried over phosphorus pentoxide.

Type 2. 2R₂O.Co₂O₃.4N₂O₃, Cobalti-tetra-nitrites or Red Cobalti-nitrites.