Sodium carbonyl ferrocyanide, Na₃[Fe(CN)₅CO]

Sodium carbonyl ferrocyanide, Na₃[Fe(CN)₅CO].7H₂O, is obtained in a similar manner to the potassium salt. It crystallises in pale yellow monoclinic needles, which become anhydrous at 110° C.

The heats of solution are as follow: -

[Na₃Fe(CN)₅.CO] + Aq. = Na₃Fe(CN)₅CO.Aq. + 4800 calories,
[Na₃Fe(CN)₅CO.7H₂O] + Aq. = Na₃Fe(CN)₅CO.Aq. -7500 calories, whence the heat of hydration of the anhydrous salt is 12,300 calories at 15.9° C.