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 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] The reaction of iron and selenic acid produces iron(II) selenate as well, but with a side product:[3] Double salts like the Tutton's salts (NH4)2Fe(SeO4)2•6H2O and K2Fe(SeO4)2•6H2O are known.