Sodium ferro-heptanitroso sulphide, NaFe₄(NO)₇S₃

Sodium ferro-heptanitroso sulphide, NaFe₄(NO)₇S₃.2H₂O, may be obtained in a similar manner to the potassium salt by boiling a solution of sodium ferro-dinitroso thiosulphate, as also by the action of sodium nitrite and sulphide solutions upon ferrous sulphate. In this latter reaction the sodium sulphide may be replaced by sodium thiocarbonate, Na₂CS₃.

The constitution of this salt has been represented as follows: -



Upon crystallisation the salt is obtained as monoclinic needles. It is more readily soluble in water than the potassium salt. It begins to decompose at 80° C., evolving nitric oxide. Heated with concentrated sulphuric acid, the salt decomposes, evolving nitric oxide, nitrogen, and hydrogen sulphide; sulphur is precipitated out, and, upon evaporating the filtered solution, ferric sulphate and sodium and ammonium sulphates are left. On the other hand, when treated with ice-cold concentrated sulphuric acid, a portion only of the sodium heptanitroso derivative is decomposed, and the liberated iron atoms replace those of sodium in the remaining unattacked portion, yielding ferrous ferro-heptanitroso sulphide, Fe[Fe₄(NO)₇S₃]₂. This salt may also be obtained by double decomposition of the sodium salt with ferrous sulphate. The resulting precipitate is washed, recrystallised from ether, and finally from water. It begins to decompose at 55° C.