Sodium ferrioxalate

Sodium ferrioxalate are inorganic compounds with the formula Na₃Fe(C₂O₄)₃(H₂O)_n. The pentahydrate has been characterized by X-ray crystallography. In contrast the potassium, ammonium, and rubidium salts crystallize from water as their trihydrates.^[2]

Sodium ferrioxalate

Names
IUPAC name Sodium iron(III) oxalate, sodium oxalatoferrate, sodium trisoxalatoferrate
Other names Sodium ferrioxalate Sodium ferric oxalate Sodium trisoxalatoferrate (III) Sodium oxalatoferrate
Identifiers
CAS Number	5936-14-1 Y 555-34-0
3D model (JSmol)	Interactive image
ChemSpider	147755
ECHA InfoCard	100.008.267
EC Number	209-092-9
PubChem CID	131855679
CompTox Dashboard (EPA)	DTXSID60890505
InChI InChI=1S/3C2H2O4.Fe.3Na/c3*3-1(4)2(5)6;;;;/h3*(H,3,4)(H,5,6);;;;/q;;;+3;3*+1/p-6 Key: XIPRSXSGWQCSHH-UHFFFAOYSA-H
SMILES O=C(C(=O)O1)O[Fe-3]123(OC(C(=O)O2)=O)OC(C(=O)O3)=O.[Na+].[Na+].[Na+]
Properties
Chemical formula	C6FeNa3O12
Molar mass	388.868 g·mol−1
Appearance	lime green hydrated crystals
Density	1.97 g/cm3 at 17 °C
Solubility in water	32.5pts per 100pts solvent, cold water, 182pts per 100pts, boiling water[1]
Structure
Coordination geometry	octahedral
Dipole moment	0 D
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Corrosive. Eye, respiratory and skin irritant.
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H312
Precautionary statements	P264, P270, P280, P301+P312, P302+P352, P312, P322, P330, P363, P501
Related compounds
Other anions	Potassium ferrioxalate
Related compounds	Iron(II) oxalate Iron(III) oxalate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

The compound is a salt consisting of ferrioxalate anions, [Fe(C₂O₄)₃]³⁻, and sodium cations Na⁺. The anion is a transition metal complex consisting of an iron atom in the +3 oxidation state and three bidentate oxalate ions C₂O2−4 anions serving as ligands.

The ferrioxalate anion is sensitive to light and higher-energy electromagnetic radiation, which causes the decomposition of one oxalate to carbon dioxide CO₂ and reduction of the iron(III) atom to iron(II).

Preparation

Sodium trisoxalatoferrate crystals

Sodium ferrioxalate can be obtained by mixing solutions of sodium oxalate and ferric oxalate, and waiting a few hours for the brown colour of the ferric oxalate to be replaced with the green colour of the complex anion.

3 Na₂C₂O₄ + Fe₂(C₂O₄)₃ → 2 Na₃[Fe(C₂O₄)₃]

The equilibrium is attained only slowly at room temperature. The product can then be crystallized by evaporating the solution at just below boiling until small crystals appear, then allowing it to cool. The product may also be precipitated by adding methanol or ethanol to the solution.

Some decomposition of the ferric oxalate may occur during the process, resulting in the canary-yellow insoluble iron(II) oxalate. Small amounts of hydrogen peroxide H₂O₂ may be added to keep the iron in the 3+ oxidation state.

See also

A number of other iron oxalates are known

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

References

1. Weast, Robert C., ed. (1981). CRC Handbook of Chemistry and Physics (62nd ed.). Boca Raton, FL: CRC Press. p. B-149. ISBN 0-8493-0462-8.
2. Armentano, Donatella; De Munno, Giovanni; Lloret, Francesc; Julve, Miguel (2005). "Bis and tris(oxalato)ferrate(III) complexes as precursors of polynuclear compounds". CrystEngComm. 7 (7): 57. doi:10.1039/b417251e.