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Iron(II) oxalate

Names
IUPAC name Iron(II) oxalate
Other names Iron oxalate Ferrous oxalate
Identifiers
CAS Number	516-03-0 6047-25-2 (dihydrate)
3D model (JSmol)	Interactive image
ECHA InfoCard	100.007.472
EC Number	208-217-4
PubChem CID	10589
UNII	DZP4YV3ICV Z6X3YBU50D (dihydrate)
CompTox Dashboard (EPA)	DTXSID4060159
InChI InChI=1S/3C2H2O4.2Fe/c3*3-1(4)2(5)6;;/h3*(H,3,4)(H,5,6);;/q;;;2*+3/p-6Key: VEPSWGHMGZQCIN-UHFFFAOYSA-H
SMILES .O=C()-C()=O
Properties
Chemical formula	FeC2O4 (anhydrous) FeC2O4 · 2 H2O (dihydrate)
Molar mass	143.86 g/mol (anhydrous) 179.89 g/mol (dihydrate)
Appearance	yellow powder
Odor	odorless
Density	2.28 g/cm
Melting point	dihydrate: 150–160 °C (302–320 °F; 423–433 K) (decomposes)
Solubility in water	dihydrate: 0.097 g/100ml (25 °C)
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H312
Precautionary statements	P280
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). N verify (what is  ?) Infobox references

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.

When heated to 120 °C, the dihydrate dehydrates, and the anhydrous ferrous oxalate decomposes near 190 °C. 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.

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

Natural occurrence

Anhydrous iron(II) oxalate is unknown among minerals as of 2020. However, the dihydrate is known as humboldtine. A related, though much more complex mineral is stepanovite,
Na ·3H₂O - an example of trioxalatoferrate(III).

See also

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

References

1. "Iron(II) oxalate dihydrate".
2. ^ Sigma-Aldrich Co., Iron(II) oxalate dihydrate. Retrieved on 2014-05-03.
3. Echigo, Takuya; Kimata, Mitsuyoshi (2008). "Single-crystal X-ray diffraction and spectroscopic studies on humboldtine and lindbergite: weak Jahn–Teller effect of Fe ion". Physics and Chemistry of Minerals. 35 (8): 467–475. Bibcode:2008PCM....35..467E. doi:10.1007/s00269-008-0241-7. S2CID 98739882.
4. Mu, Jacob; Perlmutter, D.D. (1981). "Thermal decomposition of carbonates, carboxylates, oxalates, acetates, formates, and hydroxides". Thermochimica Acta. 49 (2–3): 207–218. doi:10.1016/0040-6031(81)80175-x.
5. 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.
6. 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.
7. "Humboldtine".
8. ^ "List of Minerals". 21 March 2011.
9. "Stepanovite".

• Iron(II) compounds
• Oxalates
• Inorganic compounds