[2] Anhydrous K2Fe(C2O4)2 has been prepared by hydrothermal methods from ferrous chloride.

It is a coordination polymer with trigonal prismatic Fe(C2O4)3 centers.

[3] The material K2Fe(C2O4)2(H2O)2 has been claimed[1] but not verified.Potassium ferrooxalate is believed to be formed when the related compound potassium ferrioxalate K3[Fe(C2O4)3] is decomposed by light in solution (a common method of actinometry) or heated above 296 °C.

[1] The anhydrous salt is orange-yellow and dissolves in water to give a red solution.

Crystals of the dihydrate K2[Fe(C2O4)2]·2H2O are golden yellow in color.