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(H<sub>2</sub>O)<sub>4</sub>]SeO4•H2O, isomorphous to the corresponding iron(II) sulfate.[1] Heptahydrate is also known, in form of unstable green crystalline solid.
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.[2]
Na2SeO4 (sat.) + FeSO4 → Na2SO4 + FeSeO4The 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
Double salts like the Tutton's salts (NH4)2Fe(SeO4)2•6H2O and K2Fe(SeO4)2•6H2O are known.
In addition to the ferrous (Fe2+) salt, the ferric (Fe3+) salt iron(III) selenate, Fe2(SeO4)3, has also been reported.[4]
However, iron(II) selenite (FeSeO3) is unknown, though the selenite and pyroselenite of iron(III) was published.[5]