In contrast the potassium, ammonium, and rubidium salts crystallize from water as their trihydrates.

[2] The compound is a salt consisting of ferrioxalate anions, [Fe(C2O4)3]3−, and sodium cations Na+.

The anion is a transition metal complex consisting of an iron atom in the +3 oxidation state and three bidentate oxalate ions C2O2−4 anions serving as ligands.

The ferrioxalate anion is sensitive to light and higher-energy electromagnetic radiation, which causes the decomposition of one oxalate to carbon dioxide CO2 and reduction of the iron(III) atom to iron(II).

Small amounts of hydrogen peroxide H2O2 may be added to keep the iron in the 3+ oxidation state.