Ferric oxalate, also known as iron(III) oxalate, refers to inorganic compounds with the formula (H2O)x but could also refer to salts of 3-. (H2O)x are coordination polymers with varying degrees of hydration. The coordination complex with the formula 3- forms a variety of salts, a well-known example being potassium ferrioxalate. This article emphasizes the coordination polymers.
According to X-ray crystallography of the tetrahydrate, iron is octahedral. The oxalate ligands are bridging. Some through all four oxygen atoms, some with two oxygen atoms. Half of the water is lattice water, being situated between chains of Fe oxalates. Mössbauer spectrum of exhibits an isomer shift of 0.38 mm/s and a quadrupole splitting of 0.40 mm/s, suggesting a high spin in octahedral coordination.[1] [2]
Ferric oxalate may be produced by reaction of iron(III) hydroxide and solution of oxalic acid:
Like many oxalates, ferric oxalate has been investigated as a short-term treatment for dentin hypersensitivity.[3] It is used in certain toothpaste formulations; however, its effectiveness has been questioned.[4]
Ferric oxalate is used as the light-sensitive element in the Kallitype photographic printing process; and the platinotype process Platinum/Palladium Printing.
Ferric oxalate tetrahydrate has been investigated as a possible cheap material for the positive electrode of lithium-iron batteries. It can intercalate lithium ions at an average potential of 3.35 V, and has shown a sustainable capacity of 98 mAh/g.[1]
Ferric oxalate hexahydrate is used with sodium borohydride for radical Markovnikov hydrofunctionalization reactions of alkenes.[5]
A number of other iron oxalates are known:-