Iron(II) oxalate explained

Ferrous oxalate (iron(II) oxalate) are inorganic compound with the formula FeC₂O₄(H₂O)_x where x is 0 or 2. These are orange compounds, poorly soluble in water.

Structure and reactions

Like other iron oxalates, ferrous oxalates feature octahedral Fe centers. The dihydrate FeC₂O₄(H₂O)_x is a coordination polymer, consisting of chains of oxalate-bridged ferrous centers, each with two aquo ligands.^[1]

When heated to 120 °C, the dihydrate dehydrates, and the anhydrous ferrous oxalate decomposes near 190 °C.^[2] The products of thermal decomposition is a mixture of iron oxides and pyrophoric iron metal, as well as released carbon dioxide, carbon monoxide, and water.^[3]

Ferrous oxalates are precursors to iron phosphates, which are of value in batteries.^[4]

Natural occurrence

Anhydrous iron(II) oxalate is unknown among minerals as of 2020. However, the dihydrate is known as humboldtine.^{[5] [6]} A related, though much more complex mineral is stepanovite,
Na[Mg(H₂O)₆] [Fe³⁺(C₂O₄)₃]·3H₂O - an example of trioxalatoferrate(III).^{[7] [8]}

See also

• Iron(III) oxalate
• Potassium ferrioxalate
• Sodium ferrioxalate

Notes and References

1. Takuya . Echigo . Mitsuyoshi . Kimata . Single-crystal X-ray diffraction and spectroscopic studies on humboldtine and lindbergite: weak Jahn–Teller effect of Fe²⁺ ion . . 2008 . 35 . 8 . 467–475 . 10.1007/s00269-008-0241-7 . 2008PCM....35..467E . 98739882.
2. 10.1016/0040-6031(81)80175-x . Thermal decomposition of carbonates, carboxylates, oxalates, acetates, formates, and hydroxides . 1981 . Mu . Jacob . Perlmutter . D.D. . Thermochimica Acta . 49 . 2–3 . 207–218 .
3. Thermal Behaviour of Iron(II) Oxalate Dihydrate in the Atmosphere of Its Conversion Gases . Martin . Hermanek . Radek . Zboril . Miroslav . Mashlan . Libor . Machala . Oldrich . Schneeweiss . J. Mater. Chem. . 2006 . 16 . 13 . 1273–1280. 10.1039/b514565a.
4. 10.1038/nmat2007 . A multifunctional 3.5 V iron-based phosphate cathode for rechargeable batteries . 2007 . Ellis . B. L. . Makahnouk . W. R. M. . Makimura . Y. . Toghill . K. . Nazar . L. F. . Nature Materials . 6 . 10 . 749–753 . 17828278 . 2007NatMa...6..749E .
5. Web site: Humboldtine.
6. Web site: List of Minerals. 21 March 2011.
7. Web site: Stepanovite.
8. Web site: List of Minerals. 21 March 2011.