Iron(II) nitrate is the nitrate salt of iron(II). It is commonly encountered as the green hexahydrate, Fe(NO<sub>3</sub>)<sub>2</sub>÷6H<sub>2</sub>O, which is a metal aquo complex, however it is not commercially available unlike iron(III) nitrate due to its instability to air. The salt is soluble in water and serves as a ready source of ferrous ions.
No structure of any salt Fe(NO<sub>3</sub>)<sub>2</sub>÷xH<sub>2</sub>O has been determined by X-ray crystallography. Nonetheless, the nature of the aquo complex [Fe(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup> is well known and relatively insensitive to the anion. The Fe-O distances are longer for [Fe(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup> (2.13 à) than for the ferric analogue [Fe(H<sub>2</sub>O)<sub>6</sub>]<sup>3+</sup> (1.99 à). Both [Fe(H<sub>2</sub>O)<sub>6</sub>]<sup>n+</sup> complexes are high spin, which results in pale colors, paramagnetism, and weak Fe-O bonds.
Iron(II) nitrate can be produced in multiple ways, such as the reaction of iron metal with cold dilute nitric acid:
If this reaction is conducted below -10 ðC, nonahydrate is produced. It readily releases water to give the hexahydrate.
The above reaction can also co-produce ferric nitrate. Reacting iron(II) sulfate and lead nitrate under dilute ethanol and then evaporating the solution leads to the formation of the green crystals of the hexahydrate. A solution of iron(II) nitrate is produced by the ion-exchange reaction of iron(II) sulfate and barium nitrate, producing a concentration of up to 1.5 M due to the limited solubility of barium nitrate.
The solution of the iron(II) nitrate-hydrazine complex is produced by the reaction of hydrazine nitrate and ferric nitrate at 40 ðC with copper(II) nitrate as a catalyst:
If the compound is used in situ, the compound is produced by the reaction of iron(II) chloride and calcium nitrate:
The hexahydrate melts at 60 ðC and then decomposes at 61 ðC into iron(III) oxide rather than iron(II) oxide. A solution of iron(II) nitrate is much more stable, decomposing at 107 ðC to iron(III), with the presence of nitric acid lowering the decomposition temperature. Concentrated nitric acid oxidizes iron(II) nitrate into iron(III) nitrate:
Iron(II) nitrate has no uses, however, there is a potential use for dye removal.