Ferric oxalate

Ferric oxalate, also known as iron(III) oxalate, is a inorganic compound composed of ferric ions and oxalate ligands. It is a coordination polymer. The anhydrous material is pale yellow; however, it may be hydrated to form several hydrates, such as potassium ferrioxalate, or Fe2(C2O4)3 · 6 H2O, which is bright green in colour.

Ferric oxalate
Names
Systematic IUPAC name
iron(3+) ethanedioate (2:3)
Other names
Iron(III) oxalate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.019.047
EC Number
  • 220-951-7
UNII
  • InChI=1S/3C2H2O4.2Fe/c3*3-1(4)2(5)6;;/h3*(H,3,4)(H,5,6);;/q;;;2*+3/p-6
  • [Fe+3].[Fe+3].O=C([O-])C([O-])=O.[O-]C(=O)C([O-])=O.[O-]C(=O)C([O-])=O
Properties
C6Fe2O12
Molar mass 375.747 g/mol
Appearance Pale yellow solid (anhydrous)
Lime green solid (hexahydrate)
Odor odorless
Melting point 365.1 °C (689.2 °F)
slightly soluble
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Structure

Tetrahydrate
Structure of hydrated ferric oxalate Color code: red=O, white = H, blue = Fe, gray = C.
Room temperature Mössbauer spectrum of Fe2(C2O4)3·4H2O

According to X-ray crystallography of the tetrahydrate Fe2(C2O4)3 · 4 H2O, iron is octahedral. The oxalate ligand]]s are bridging. Some through all four oxygen atoms, some with two oxygen atoms. Half of the water is lattice water, being situated between chains of Fe oxalates. Mössbauer spectrum of Fe2(C2O4)3 · 4 H2O exhibits an isomer shift of 0.38 mm/s and a quadrupole splitting of 0.40 mm/s, suggesting a high spin Fe3+ in octahedral coordination.[1]

Uses

Dentistry

Like many oxalates, ferric oxalate has been investigated as a short-term treatment for dentin hypersensitivity.[2] It is used in certain toothpaste formulations; however, its effectiveness has been questioned.[3]

Photography

Ferric oxalate is used as the light-sensitive element in the Kallitype photographic printing process; and the platinotype process Platinum/Palladium Printing.

Batteries

Ferric oxalate tetrahydrate has been investigated as a possible cheap material for the positive electrode of lithium-iron batteries. It can intercalate lithium ions at an average potential of 3.35 V, and has shown a sustainable capacity of 98 mAh/g.[1]

Organic synthesis

Ferric oxalate hexahydrate is used with sodium borohydride for radical Markovnikov hydrofunctionalization reactions of alkenes.[4]

See also

A number of other iron oxalates are known:-

References
  1. Ahouari, Hania; Rousse, Gwenaëlle; Rodríguez-Carvajal, Juan; Sougrati, Moulay-Tahar; Saubanère, Matthieu; Courty, Matthieu; Recham, Nadir; Tarascon, Jean-Marie (2015). "Unraveling the Structure of Iron(III) Oxalate Tetrahydrate and Its Reversible Li Insertion Capability". Chemistry of Materials. 27 (5): 1631–1639. doi:10.1021/cm5043149.
  2. Gillam, D. G.; Newman, H. N.; Davies, E. H.; Bulman, J. S.; Troullos, E. S.; Curro, F. A. (2004). "Clinical evaluation of ferric oxalate in relieving dentine hypersensitivity". Journal of Oral Rehabilitation. 31 (3): 245–250. doi:10.1046/j.0305-182X.2003.01230.x. PMID 15025657.
  3. Cunha-Cruz, J.; Stout, J. R.; Heaton, L. J.; Wataha, J. C. (29 December 2010). "Dentin Hypersensitivity and Oxalates: a Systematic Review". Journal of Dental Research. 90 (3): 304–310. doi:10.1177/0022034510389179. PMC 3144108. PMID 21191127.
  4. Barker, Timothy (2001-04-15). "Ferric Oxalate Hexahydrate". Encyclopedia of Reagents for Organic Synthesis (1 ed.). Wiley. pp. 1–4. doi:10.1002/047084289X.rn02346. ISBN 978-0-471-93623-7. S2CID 225482606.
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