This complex has been of my interest for quite a long while now, but I couldn’t make it because of lack of reagents or my inability to find a good procedure for it.
Now, that I’m generally better at inorganic chemistry, I’ve managed to adapt an old preparation of it for the modern (home) chemist. (I’m not using lead as an oxidizer)
Sodium Cobalt Nitrite
1.54 grams of cobalt (II) sulfate hexahydrate (0.01 mol) were dissolved in 7.5 ml of water with the help of strong stirring and heating. A similar solution of 13.6 grams (0.2 mol) of sodium nitrite in 7.5 ml was also prepared with the help of strong heating and stirring.
The nitrite solution was placed on a stirring hotplate, and the cobalt sulfate solution was added to it at once with no visible colour change.
After letting it stir for a little while, 5 ml of glacial acetic acid were added, after which the solution heated up considerably, and released an amount of terrible red NO2 gas.
Once gas evolution subsided, ~20 ml of 3% hydrogen peroxide were slowly added, and the solution was left stirring for about 10 minutes.
The solution was vacuum filtered, and the precipitate discarded. This is a solution of the highly soluble sodium salt of the nitro complex.
Potassium Cobalt Nitrite
A solution of ~5 grams of potassium chloride was prepared in warm distilled water, and the brown-red sodium salt solution was added to it at once. A yellow precipitate was formed and allowed to settle for 10 minutes. The precipitate was vacuum filtered on a fritted glass buchner funnel (the particle size clogs paper filters), and washed with distilled water.
The solid was allowed to dry in a desiccator overnight, and then in hot air, to speed up the drying process (I am very impatient).
The final yield as 4.52 grams, which is 46% of theoretical.
