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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/c33-1(4)2(5)6;;/h3(H,3,4)(H,5,6);;/q;;;2*+3/p-6 Key: VEPSWGHMGZQCIN-UHFFFAOYSA-H ;
	SMILES [Fe+2].O=C([O-])-C([O-])=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/cm3
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 [77 °F], 100 kPa). 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.^[3]

When heated to 120 °C, the dihydrate dehydrates, and the anhydrous ferrous oxalate decomposes near 190 °C.^[4] 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.^[5]

Ferrous oxalates are precursors to iron phosphates, which are of value in batteries.^[6]

Natural occurrence

Anhydrous iron(II) oxalate is unknown among minerals as of 2020. However, the dihydrate is known as humboldtine.^[7]^[8] A related, though much more complex mineral is stepanovite,
Na[Mg(H₂O)₆] [Fe³⁺(C₂O₄)₃]·3H₂O - an example of trioxalatoferrate(III).^[9]^[8]

References

^ "Iron(II) oxalate dihydrate".
^ ^a ^b ^c Sigma-Aldrich Co., Iron(II) oxalate dihydrate. Retrieved on 2014-05-03.
^ 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.
^ 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.
^ 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.
^ 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.
^ "Humboldtine".
^ ^a ^b "List of Minerals". 21 March 2011.
^ "Stepanovite".