Iron(II) selenate

Iron(II) selenate (ferrous selenate) is an inorganic compound with the formula FeSeO₄. It has anhydrous and several hydrate forms. The pentahydrate has the structure, [Fe(H₂O)₄]SeO₄•H₂O, isomorphous to the corresponding iron(II) sulfate.^[2] Heptahydrate is also known, in form of unstable green crystalline solid.^[3]

Iron(II) selenate

Names
Other names Ferrous selenate
Identifiers
CAS Number	(anhydrous): 15857-43-9[1] (pentahydrate): 70807-08-8
3D model (JSmol)	(anhydrous): Interactive image (pentahydrate): Interactive image
PubChem CID	(anhydrous): 159739849
InChI (anhydrous): InChI=1S/Fe.H2O4Se/c;1-5(2,3)4/h;(H2,1,2,3,4)/q+2;/p-2 Key: NCHUFZYUFAWBQI-UHFFFAOYSA-L (pentahydrate): InChI=1S/Fe.H2O4Se.5H2O/c;1-5(2,3)4;;;;;/h;(H2,1,2,3,4);5*1H2/q+2;;;;;;/p-2 Key: YXLBLVIIVLRXHU-UHFFFAOYSA-L
SMILES (anhydrous): [O-][Se](=O)(=O)[O-].[Fe+2] (pentahydrate): [O-][Se](=O)(=O)[O-].[Fe+2].O.O.O.O.O
Properties
Chemical formula	FeSeO4
Molar mass	198.8046 g/mol (anhydrous) 288.881 g/mol (pentahydrate) 324.91156 g/mol (heptahydrate)
Appearance	green, unstable crystalline solid (heptahydrate)
Solubility in water	soluble
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Preparation

Iron(II) selenate can be prepared by the reaction of saturated sodium selenate and iron(II) sulfate at 80 °C. When cooled to room temperature, crystalline iron(II) selenate precipitates from the solution.^[4]

Na₂SeO₄ (sat.) + FeSO₄ → Na₂SO₄ + FeSeO₄

The reaction of iron and selenic acid produces iron(II) selenate as well, but with a side product:^[3]

Fe + H₂SeO₄ → FeSeO₄ + H₂↑

3 Fe + 4 H₂SeO₄ → 3 FeSeO₄ + Se + 4 H₂O

Other species containing oxoanion of selenium

Double salts like the Tutton's salts (NH₄)₂Fe(SeO₄)₂•6H₂O and K₂Fe(SeO₄)₂•6H₂O are known.^[3]

In addition to the ferrous (Fe²⁺) salt, the ferric (Fe³⁺) salt iron(III) selenate, Fe₂(SeO₄)₃, has also been reported.^[5]

However, iron(II) selenite (FeSeO₃) is unknown, though the selenite and pyroselenite of iron(III) was published.^[6]