Ferro-dinitroso Sulphides, MFe(NO)₂S

On boiling potassium ferro-heptanitroso sulphide with dilute potassium hydroxide, ferric hydroxide is deposited, and, upon concentration of the filtered liquid, dark red crystals of potassium ferro-dinitroso sulphide are obtained, to which the formula KFe(NO)₂S.2H₂O is ascribed. The reaction may be represented as follows: -

2KFe₄(NO)₇S₃ + 4KOH = 6KFe(NO)₂S + Fe₂O₃ + N₂O + 2H₂O.

The reverse transformation is effected by treatment with carbon dioxide, dilute acids, or ferrous chloride.

The sodium salt, NaFe(NO)₂S.4H₂O, may be prepared in an analogous manner. It was the first salt of this series to be obtained, and Roussin, its discoverer, gave to it a formula which, translated into modern equivalents, becomes 3Na₂S.Fe₂S₃(NO)₂.

The ammonium salt cannot be obtained by boiling the ammonium hepta derivative with ammonium hydroxide, nor by the action of ammonia upon the free acid. It results, however, when the free acid is treated with ammonium sulphide. It is very unstable. The caesium, iron, and thallium salts have been prepared. The last-named is quite insoluble in water and in alcohol.

The free acid is obtained by decomposing the sodium or potassium

salt with dilute mineral acid. It is a yellowish brown amorphous substance, insoluble in water, more soluble in alcohol, and readily soluble in carbon disulphide. It slowly decomposes on standing.