Iron(II) oxalate

Ferrous oxalate (iron(II) oxalate) refers to inorganic compounds with the formula FeC₂O₄(H₂O)_x where x is 0 or 2. These are yellow compounds. Characteristic of metal oxalate complexes, these compounds tend to be polymeric, hence their low solubility in water.

Iron(II) oxalate

Names
IUPAC name Iron(II) oxalate
Other names Iron oxalate Ferrous oxalate
Identifiers
CAS Number	(anhydrous): 516-03-0 Y (dihydrate): 6047-25-2 Y
3D model (JSmol)	(anhydrous): Interactive image (dihydrate): Interactive image
ChemSpider	(anhydrous): 10144 (dihydrate): 450862
ECHA InfoCard	100.007.472
EC Number	(anhydrous): 208-217-4 (dihydrate): 611-981-5
PubChem CID	(anhydrous): 10589 (dihydrate): 516788
UNII	(anhydrous): DZP4YV3ICV Y (dihydrate): Z6X3YBU50D Y
CompTox Dashboard (EPA)	DTXSID4060159 (dihydrate): DTXSID90975879
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 · 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)[1]
Hazards
GHS labelling:
Pictograms	[2]
Signal word	Warning
Hazard statements	H302, H312[2]
Precautionary statements	P280[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

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, although much more complex mineral is stepanovite.
Na[Mg(H₂O)₆][Fe(III)(C₂O₄)₃]·3H₂O is an unusual example of a naturally-occurring ferrioxalate.^[9][8]

See also

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