Ferric oxalate
{{Chembox
|ImageFile = Ferric oxalate.svg
|SystematicName = iron(3+) ethanedioate (2:3)
|OtherNames = Iron(III) oxalate
|Section1 = {{Chembox Identifiers
|CASNo = 2944-66-3
|CASNo_Comment = (Anhydrous)
|CASNo1 = 166897-40-1
|CASNo1_Comment = (hexahydrate)
|CASNo_Ref = {{cascite|correct|CAS}}
|UNII_Ref = {{fdacite|correct|FDA}}
|UNII = DTJ9P8AB5L
|EINECS = 220-951-7
|PubChem = 168963
|ChemSpiderID = 147789
|SMILES = [Fe+3].[Fe+3].O=C([O-])C([O-])=O.[O-]C(=O)C([O-])=O.[O-]C(=O)C([O-])=O
|InChI = InChI=1S/3C2H2O4.2Fe/c3*3-1(4)2(5)6;;/h3*(H,3,4)(H,5,6);;/q;;;2*+3/p-6
}}
|Section2 = {{Chembox Properties
|Formula = C6Fe2O12
|MolarMass = 375.747 g/mol
|Appearance = Pale yellow solid (anhydrous)
Lime green solid (hexahydrate)
|Odor = odorless
|MeltingPt = {{convert|365.1|C|F}}
|Solubility = slightly soluble
}}
}}
Ferric oxalate, also known as iron(III) oxalate, refers to inorganic compounds with the formula {{chem2|Fe2(C2O4)3}}(H2O)x but could also refer to salts of {{chem2|[Fe(C2O4)3]}}3-. {{chem2|Fe2(C2O4)3}}(H2O)x are coordination polymers with varying degrees of hydration. The coordination complex with the formula {{chem2|[Fe(C2O4)3]}}3- forms a variety of salts, a well-known example being potassium ferrioxalate. This article emphasizes the coordination polymers.
Structure
=Tetrahydrate=
According to X-ray crystallography of the tetrahydrate {{chem2|Fe2(C2O4)3 * 4 H2O}}, iron is octahedral. The oxalate ligands 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 {{chem2|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 {{chem2|Fe(3+)}} in octahedral coordination.{{cite journal | last1 = Ahouari | first1 = Hania | last2 = Rousse | first2 = Gwenaëlle | last3 = Rodríguez-Carvajal | first3 = Juan | last4 = Sougrati | first4 = Moulay-Tahar | last5 = Saubanère | first5 = Matthieu | last6 = Courty | first6 = Matthieu | last7 = Recham | first7 = Nadir | last8 = Tarascon | first8 = Jean-Marie | year = 2015 | title = Unraveling the Structure of Iron(III) Oxalate Tetrahydrate and Its Reversible Li Insertion Capability | journal = Chemistry of Materials | volume = 27 | issue = 5| pages = 1631–1639 | doi = 10.1021/cm5043149 }}{{cite journal |doi=10.1039/C6DT02740G |title=Oxalate-mediated long-range antiferromagnetism order in Fe2(C2O4)3·4H2O |date=2016 |last1=Rousse |first1=G. |last2=Rodríguez-Carvajal |first2=J. |journal=Dalton Transactions |volume=45 |issue=36 |pages=14311–14319 |pmid=27539964 }}
Production
Ferric oxalate may be produced by reaction of iron(III) hydroxide and solution of oxalic acid:
:{{chem2|2Fe(OH)3 + 3H2C2O4 -> Fe2(C2O4)3 + 6H2O}}
Uses
=Dentistry=
Like many oxalates, ferric oxalate has been investigated as a short-term treatment for dentin hypersensitivity.{{cite journal|last1=Gillam|first1=D. G.|last2=Newman|first2=H. N.|last3=Davies|first3=E. H.|last4=Bulman|first4=J. S.|last5=Troullos|first5=E. S.|last6=Curro|first6=F. A.|title=Clinical evaluation of ferric oxalate in relieving dentine hypersensitivity|journal=Journal of Oral Rehabilitation|volume=31|issue=3|pages=245–250|doi=10.1046/j.0305-182X.2003.01230.x|year=2004|pmid=15025657 }} It is used in certain toothpaste formulations; however, its effectiveness has been questioned.{{cite journal|last1=Cunha-Cruz|first1=J.|last2=Stout|first2=J. R.|last3=Heaton|first3=L. J.|last4=Wataha|first4=J. C.|title=Dentin Hypersensitivity and Oxalates: a Systematic Review|journal=Journal of Dental Research|date=29 December 2010|volume=90|issue=3|pages=304–310|doi=10.1177/0022034510389179|pmc=3144108|pmid=21191127}}
=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.
= Organic synthesis =
Ferric oxalate hexahydrate is used with sodium borohydride for radical Markovnikov hydrofunctionalization reactions of alkenes.{{Cite book|url=https://onlinelibrary.wiley.com/doi/book/10.1002/047084289X|title=Encyclopedia of Reagents for Organic Synthesis|date=2001-04-15|publisher=Wiley|isbn=978-0-471-93623-7|edition=1|language=en|chapter=Ferric Oxalate Hexahydrate|doi=10.1002/047084289X.rn02346|last1=Barker |first1=Timothy |pages=1–4 |s2cid=225482606 }}
See also
A number of other iron oxalates are known:-