Iron(II) oxalate

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Iron(II) oxalate
IUPAC name
Iron(II) oxalate
Other names
Iron oxalate
Ferrous oxalate
3D model (JSmol)
ECHA InfoCard 100.007.472 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 208-217-4
PubChem CID
  • InChI=1S/3C2H2O4.2Fe/c3*3-1(4)2(5)6;;/h3*(H,3,4)(H,5,6);;/q;;;2*+3/p-6 X mark.svgN
  • [Fe+2].O=C([O-])-C([O-])=O
FeC2O4 (anhydrous)
FeC2O4 · 2 H2O (dihydrate)
Molar mass 143.86 g/mol (anhydrous)
179.89 g/mol (dihydrate)
Appearanceyellow powder
Odor odorless
Density 2.28 g/cm3
Melting point 190 °C (374 °F; 463 K)
(anhydrous) [1]
150–160 °C (302–320 °F; 423–433 K)
(dihydrate) decomposes
Boiling point 365.1 °C (689.2 °F; 638.2 K)
(anhydrous) [1]
0.097 g/100ml (25 °C) [2]
GHS labelling:
GHS-pictogram-exclam.svg [3]
H302, H312 [3]
P280 [3]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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



The dihydrate FeC2O4 · 2 H2O is a coordination polymer, consisting of chains of oxalate-bridged ferrous centers, each with two aquo ligands. [4]

When heated, it dehydrates and decomposes into a mixture of iron oxides and pyrophoric iron metal, with release of carbon dioxide, carbon monoxide, and water. [5]

Natural occurrence

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

See also

A number of other iron oxalates are known

Related Research Articles

Iron Chemical element, symbol Fe and atomic number 26

Iron is a chemical element with symbol Fe and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in front of oxygen, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust.

Ferrous Adjective denoting something as containing iron, or, in chemistry, a compound containing iron in the +2 oxidation state

In chemistry, the adjective Ferrous indicates a compound that contains iron(II), meaning iron in its +2 oxidation state, possibly as the divalent cation Fe2+. It is opposed to "ferric" or iron(III), meaning iron in its +3 oxidation state, such as the trivalent cation Fe3+. This usage has been largely replaced by the IUPAC nomenclature, which calls for the oxidation state being indicated by Roman numerals in parentheses, such as iron(II) oxide for ferrous oxide (FeO), iron(III) oxide for ferric oxide (Fe2O3), and iron(II,III) oxide for the oxide Fe3O4 that contains both forms of iron.

Iron(II) sulfate Chemical compound

Iron(II) sulfate (British English: iron(II) sulphate) or ferrous sulfate denotes a range of salts with the formula FeSO4·xH2O. These compounds exist most commonly as the heptahydrate (x = 7) but several values for x are known. The hydrated form is used medically to treat iron deficiency, and also for industrial applications. Known since ancient times as copperas and as green vitriol (vitriol is an archaic name for sulfate), the blue-green heptahydrate (hydrate with 7 molecules of water) is the most common form of this material. All the iron(II) sulfates dissolve in water to give the same aquo complex [Fe(H2O)6]2+, which has octahedral molecular geometry and is paramagnetic. The name copperas dates from times when the copper(II) sulfate was known as blue copperas, and perhaps in analogy, iron(II) and zinc sulfate were known respectively as green and white copperas.

Oxalic acid Simplest dicarboxylic acid

Oxalic acid is an organic acid with the IUPAC name ethanedioic acid and formula HO2C−CO2H. It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name comes from the fact that early investigators isolated oxalic acid from flowering plants of the genus Oxalis, commonly known as wood-sorrels. It occurs naturally in many foods, but excessive ingestion of oxalic acid or prolonged skin contact can be dangerous.

Water of crystallization

In chemistry, water(s) of crystallization or water(s) of hydration are water molecules that are present inside crystals. Water is often incorporated in the formation of crystals from aqueous solutions. In some contexts, water of crystallization is the total mass of water in a substance at a given temperature and is mostly present in a definite (stoichiometric) ratio. Classically, "water of crystallization" refers to water that is found in the crystalline framework of a metal complex or a salt, which is not directly bonded to the metal cation.

Iron(II) chloride Chemical compound

Iron(II) chloride, also known as ferrous chloride, is the chemical compound of formula FeCl2. It is a paramagnetic solid with a high melting point. The compound is white, but typical samples are often off-white. FeCl2 crystallizes from water as the greenish tetrahydrate, which is the form that is most commonly encountered in commerce and the laboratory. There is also a dihydrate. The compound is highly soluble in water, giving pale green solutions.

Iron(II) carbonate, or ferrous carbonate, is a chemical compound with formula FeCO
, that occurs naturally as the mineral siderite. At ordinary ambient temperatures, it is a green-brown ionic solid consisting of iron(II) cations Fe2+
and carbonate anions CO2−

Potassium ferrioxalate Chemical compound

Potassium ferrioxalate, also called potassium trisoxalatoferrate or potassium tris(oxalato)ferrate(III) is a chemical compound with the formula K
]. It often occurs as the trihydrate K3[Fe(C2O4)3]·3H2O. Both are crystalline compounds, lime green in colour.

Iron(II) The element iron in its +2 oxidation state

In chemistry, iron(II) refers to the element iron in its +2 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe2+.

Sodium ferrioxalate Chemical compound

Sodium ferrioxalate is a chemical compound with the formula Na3Fe(C2O4)3. It is also called sodium oxalatoferrate or sodium trisoxalatoferrate.

Ferric oxalate Chemical compound

Ferric oxalate, also known as iron(III) oxalate, is a chemical compound composed of ferric ions and oxalate ligands; it may also be regarded as the ferric salt of oxalic acid. The anhydrous material is pale yellow; however, it may be hydrated to form several hydrates, such as potassium ferrioxalate, or Fe2(C2O4)3 · 6 H2O, which is bright green in colour.

Magnesium oxalate Magnesium compound

Magnesium oxalate is an organic compound comprising a magnesium cation with a 2+ charge bonded to an oxalate anion. It has the chemical formula MgC2O4. Magnesium oxalate is a white solid that comes in two forms: an anhydrous form and a dihydrate form where two water molecules are complexed with the structure. Both forms are practically insoluble in water and are insoluble in organic solutions.

Chromium(II) oxalate is an inorganic compound with the chemical formula CrC2O4.

The oxalatonickelates are a class of compounds that contain nickel complexed by oxalate groups. They form a series of double salts, and include clusters with multiple nickel atoms. Since oxalate functions as a bidentate ligand it can satisfy two coordinate positions around the nickel atom, or it can bridge two nickel atoms together.

Potassium ferrooxalate, also known as potassium bisoxalatoferrate(II), is a salt with the formula K
], sometimes abbreviated K
. The ferrooxalate anion [Fe(C
is a transition metal complex, consisting of an atom of iron in the +2 oxidation state bound to two bidentate oxalate ions C
. The anion charge is balanced by two cations of potassium K+

Caesium oxalate (standard IUPAC spelling) dicesium oxalate, or cesium oxalate (American spelling) is the oxalate of caesium. Caesium oxalate has the chemical formula of Cs2C2O4.

The nickel organic acid salts are organic acid salts of nickel. In many of these the ionised organic acid acts as a ligand.

Ferrioxalate Ion

Ferrioxalate or trisoxalatoferrate(III) is a trivalent anion with formula [Fe(C2O4)3]3−. It is a transition metal complex consisting of an iron atom in the +3 oxidation state and three bidentate oxalate ions C2O2−4 anions acting as ligands.

Manganese oxalate is a chemical compound, a salt of manganese and oxalic acid with the chemical formula MnC
. The compound creates light pink crystals, does not dissolve in water, and forms crystalline hydrates. It occurs naturally as the mineral Lindbergite.


Humboldtine is a rarely occurring mineral from the mineral class of "organic compounds" with the chemical composition FeC2O4•2H2O and is therefore a water-containing iron(II) oxalate or the iron salt of oxalic acid.


  1. 1 2 "CAS 516-03-0 products price,suppliers".
  2. "Iron(II) oxalate dihydrate".
  3. 1 2 3 Sigma-Aldrich Co., Iron(II) oxalate dihydrate. Retrieved on 2014-05-03.
  4. Echigo, Takuya; Kimata, Mitsuyoshi (2008). "Single-crystal X-ray diffraction and spectroscopic studies on humboldtine and lindbergite: weak Jahn–Teller effect of Fe2+ ion". Phys. Chem. Minerals . 35 (8): 467–475. Bibcode:2008PCM....35..467E. doi:10.1007/s00269-008-0241-7. S2CID   98739882.
  5. Hermanek, Martin; Zboril, Radek; Mashlan, Miroslav; et al. (2006). "Thermal behaviour of iron(II) oxalate dihydrate in the atmosphere of its conversion gases". J. Mater. Chem. 16 (13): 1273–1280. doi:10.1039/b514565a.
  6. "Humboldtine".
  7. 1 2 "List of Minerals". 21 March 2011.
  8. "Stepanovite".