Iron(II) oxalate

Iron(II) oxalate
Names
IUPAC name
Iron(II) oxalate
Systematic IUPAC name
Iron, diaqua(ethanedioato(2-)-O,O')- (dihydrate)
Other names
  • Iron oxalate
  • Ferrous oxalate
Identifiers
CAS Number
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.007.472
EC Number
  • (anhydrous): 208-217-4
  • (dihydrate): 611-981-5
PubChem CID
UNII
CompTox Dashboard (EPA)
InChI
  • InChI=1S/3C2H2O4.2Fe/c3*3-1(4)2(5)6;;/h3*(H,3,4)(H,5,6);;/q;;;2*+3/p-6 ☒N
    Key: VEPSWGHMGZQCIN-UHFFFAOYSA-H ☒N
  • (dihydrate): InChI=1S/C2H2O4.Fe.2H2O/c3-1(4)2(5)6;;;/h(H,3,4)(H,5,6);;2*1H2/q;+2;;/p-2
    Key: NPLZZSLZTJVZSX-UHFFFAOYSA-L
SMILES
  • (anhydrous): [Fe+2].O=C([O-])-C([O-])=O
  • (dihydrate): C(=O)(C(=O)[O-])[O-].O.O.[Fe+2]
Properties
Chemical formula
  • FeC2O4 (anhydrous)
  • FeC2O4·2H2O (dihydrate)
Molar mass
  • 143.86 g⋅mol−1 (anhydrous)
  • 179.89 g⋅mol−1 (dihydrate)
Appearance yellow powder
Odor odorless
Density 2.28 g/cm3[1]
Melting point
  • ~120 °C (248 °F; 393 K) (dihydrate, decomposes to anhydrous)
  • 190 °C (374 °F; 463 K) (anhydrous, decomposes)
Solubility in water
 0.097 g/100g (dihydrate)[2]
Hazards
GHS labelling:[1]
Pictograms
 GHS07: Exclamation mark
Signal word
 Warning
Hazard statements
 H302+H312
Precautionary statements
 P264, P270, P280, P301+P312+P330, P302+P352+P312, P363, P501
NFPA 704 (fire diamond)
[3]
NFPA 704 four-colored diamond
2
1
1
Threshold limit value (TLV)
 1 mg/m3[1] (TWA)
NIOSH (US health exposure limits):[3]
PEL (Permissible)
 1 mg/m3 (TWA, vacated)
REL (Recommended)
 1 mg/m3 (TWA)
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 (iron(II) oxalate) refers to the inorganic compound with the formula FeC2O4 (anhydrous) or FeC2O4·2H2O (dihydrate). These are yellow compounds. Characteristic of metal oxalate complexes, these compounds tend to be polymeric, hence their low solubility in water. The dihydrate is hygroscopic.[1]

Structure

Like other iron oxalates, ferrous oxalates feature octahedral Fe centers. The dihydrate FeC2O4·2H2O is a coordination polymer, consisting of chains of oxalate-bridged ferrous centers, each with two aquo ligands.[4]
Ball-and-stick model of a chain in the crystal structure of iron(II) oxalate dihydrate

Reactions

When heated to 120 °C (248 °F), the dihydrate dehydrates, and the anhydrous ferrous oxalate decomposes near 190 °C (374 °F).[5] The products of thermal decomposition in a sealed environment are a mixture of iron oxides, pyrophoric iron, carbon dioxide, carbon monoxide, and water.[6]

Ferrous oxalates are precursors to iron phosphates, which are of value in batteries.[7]

Natural occurrence

Anhydrous iron(II) oxalate is unknown among minerals as of 2020. However, the dihydrate is known as humboldtine.[8] A related mineral is stepanovite (Na[Mg(H2O)6][Fe(C2O4)3]·3H2O), an unusual example of a naturally occurring ferrioxalate.[9]

See also

References

  1. ^ a b c d Sigma-Aldrich Co., Iron(II) oxalate dihydrate. Retrieved on 2025-12-20.
  2. ^ Kiper, R.A. (ed.). "Iron(II) oxalate dihydrate". chemister.ru. Retrieved 2025-12-20.
  3. ^ a b "SDS - Iron(II) oxalate dihydrate" (pdf). fishersci.com. ThermoFisher Scientific. 30 March 2024. p. 3. Retrieved 20 December 2025.
  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". Physics and Chemistry of Minerals. 35 (8): 467–475. Bibcode:2008PCM....35..467E. doi:10.1007/s00269-008-0241-7. S2CID 98739882.
  5. ^ Mu, Jacob; Perlmutter, D.D. (1981). "Thermal decomposition of carbonates, carboxylates, oxalates, acetates, formates, and hydroxides". Thermochimica Acta. 49 (2–3): 207–218. Bibcode:1981TcAc...49..207M. doi:10.1016/0040-6031(81)80175-x.
  6. ^ Hermanek, Martin; Zboril, Radek; Mashlan, Miroslav; Machala, Libor; Schneeweiss, Oldrich (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.
  7. ^ Ellis, B. L.; Makahnouk, W. R. M.; Makimura, Y.; Toghill, K.; Nazar, L. F. (2007). "A multifunctional 3.5 V iron-based phosphate cathode for rechargeable batteries". Nature Materials. 6 (10): 749–753. Bibcode:2007NatMa...6..749E. doi:10.1038/nmat2007. PMID 17828278.
  8. ^ "Humboldtine". mindat.org. Retrieved 20 December 2025.
  9. ^ "Stepanovite". mindat.org. Retrieved 20 December 2025.
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