Ferrate(VI)

Ferrate(VI)
Aromatic skeletal formula of ferrate
Aromatic skeletal formula of ferrate
Solutions of ferrate (left)
and permanganate (right)
Names
IUPAC name
Ferrate(VI)
Systematic IUPAC name
Tetraoxidoferrate(VI)
Other names
[FeO4]2-
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
2055
  • InChI=1S/Fe.4O/q;;;2*-1 checkY
    Key: XGBDPAYTQGQHEW-UHFFFAOYSA-N checkY
  • InChI=1/Fe.4O/q;;;2*-1/rFeO4/c2-1(3,4)5/q-2
    Key: XGBDPAYTQGQHEW-WTZHFVRHAI
  • [O-][Fe]([O-])(=O)=O
  • [O-][Fe](=O)(=O)[O-]
Properties
[FeO4]2-
Molar mass 119.843 g mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkYX markN ?)

Ferrate(VI) is the inorganic anion with the chemical formula [FeO4]2−. It is photosensitive, contributes a pale violet colour to compounds and solutions containing it and is one of the strongest water-stable oxidizing species known. Although it is classified as a weak base, concentrated solutions containing ferrate(VI) are corrosive and attack the skin and are only stable at high pH. It is similar to the somewhat more stable permanganate.

Nomenclature

The term ferrate is normally used to mean ferrate(VI), although it can refer to other iron-containing anions, many of which are more commonly encountered than salts of [FeO4]2−.

In battery electrochemistry, ferrate(VI) is sometimes called "super-iron".

Synthesis

Ferrate(VI) salts are formed by oxidizing iron in an aqueous medium with strong oxidizing agents under alkaline conditions, or in the solid state by heating a mixture of iron filings and powdered potassium nitrate.

For example, ferrates are produced by heating iron(III) hydroxide with sodium hypochlorite in alkaline solution:

2 Fe(OH)
3 + 3 OCl−
 + 4  OH− → 2 [FeO
4]2−
 + 5 H2O + 3 Cl−

The anion is typically precipitated as the barium(II) salt, forming barium ferrate.

Properties

Fe(VI) is a strong oxidizing agent over the entire pH range, with a reduction potential (Fe(VI)/Fe(III) couple) varying from +2.2 V to +0.7 V versus SHE in acidic and basic media respectively.

[FeO
4]2−
 + 8  H+ + 3 e− ⇌ Fe3+
 + 4 H2O; E0 = +2.20 V (acidic medium)
[FeO
4]2−
 + 4 H2O + 3 e− ⇌ Fe(OH)
3 + 5 OH−
; E0 = +0.72 V (basic medium)

Because of this, the ferrate(VI) anion is unstable at neutral or acidic pH values, decomposing to iron(III). The reduction goes through intermediate species in which iron has oxidation states +5 and +4. These anions are even more reactive than ferrate(VI). In alkaline conditions ferrates are more stable, lasting for about 8 to 9 hours at pH 8 or 9.

Aqueous solutions of ferrates are pink when dilute, and deep red or purple at higher concentrations. The ferrate ion is a stronger oxidizing agent than permanganate, and oxidizes ammonia to molecular nitrogen.

The ferrate(VI) ion has two unpaired electrons and is thus paramagnetic. It has a tetrahedral molecular geometry, isostructural with the chromate and permanganate ions.

Applications

Ferrate(VI) has been proposed as an environmentally-friendly chemical for water treatment, as its byproduct is essentially rust. Ferrate(VI) is an excellent disinfectant, capable of removing and destroying an living organism, even viruses.

Owing to its instability and the absence of a easy synthesis, ferrate(VI) solutions are impractical for water treatment. In one approach sodium ferrate is produced electrochemically at the point of use by anodic dissolution of iron in concentrated sodium hydroxide. In Russia, such generators have been developed by the Saint Petersburg company Dobrokhim.

See also

References

  1. ↑ Graham Hill; John Holman (2000). Chemistry in context (5th ed.). Nelson Thornes. p. 202. ISBN 0-17-448276-0.
  2. ↑ Licht, Stuart; Wang, Baohui; Ghosh, Susanta (1999-08-13). "Energetic Iron(VI) Chemistry: The Super-Iron Battery". Science. 285 (5430): 1039–1042. doi:10.1126/science.285.5430.1039. ISSN 0036-8075. PMID 10446044.
  3. ↑ Licht, Stuart; Naschitz, Vera; Halperin, Leonid; Halperin, Nadezhda; Lin, Lin; Chen, Jianjun; Ghosh, Susanta; Liu, Bing (2001-10-15). "Analysis of ferrate(VI) compounds and super-iron Fe(VI) battery cathodes: FTIR, ICP, titrimetric, XRD, UV/VIS, and electrochemical characterization". Journal of Power Sources. 101 (2): 167–176. Bibcode:2001JPS...101..167L. doi:10.1016/S0378-7753(01)00786-8. ISSN 0378-7753.
  4. 1 2 R. K. Sharma (2007). Text Book Of Coordination Chemistry. Discovery Publishing House. pp. 124–125. ISBN 978-81-8356-223-2.
  5. 1 2 3 Gary Wulfsberg (1991). Principles of descriptive inorganic chemistry. University Science Books. pp. 142–143. ISBN 0-935702-66-0.
  6. 1 2 3 Egon Wiberg; Nils Wiberg; Arnold Frederick Holleman (2001). Inorganic chemistry. Academic Press. pp. 1457–1458. ISBN 0-12-352651-5.
  7. 1 2 Gary M. Brittenham (1994). Raymond J. Bergeron (ed.). The Development of Iron Chelators for Clinical Use. CRC Press. pp. 37–38. ISBN 0-8493-8679-9.
  8. ↑ John Daintith, ed. (2004). Oxford dictionary of chemistry (5th ed.). Oxford University Press. p. 235. ISBN 0-19-860918-3.
  9. ↑ Kenneth Malcolm Mackay; Rosemary Ann Mackay; W. Henderson (2002). Introduction to modern inorganic chemistry (6th ed.). CRC Press. pp. 334–335. ISBN 0-7487-6420-8.
  10. ↑ Karlis Svanks (June 1976). "Oxidation of Ammonia in Water by Ferrates(VI) and (IV)" (PDF). Water Resources Center, Ohio State University. p. 3. Retrieved 2010-05-04.
  11. ↑ Sharma, Virender K.; Zboril, Radek; Varma, Rajender S. (2015). "Ferrates: Greener Oxidants with Multimodal Action in Water Treatment Technologies". Accounts of Chemical Research. 48 (2): 182–191. doi:10.1021/ar5004219. ISSN 0001-4842. PMID 25668700.
  12. ↑ Stanley E. Manahan (2005). Environmental chemistry (8th ed.). CRC Press. p. 234. ISBN 1-56670-633-5.
  13. ↑ Licht, Stuart; Yu, Xingwen (2005-10-01). "Electrochemical Alkaline Fe(VI) Water Purification and Remediation". Environmental Science & Technology. 39 (20): 8071–8076. Bibcode:2005EnST...39.8071L. doi:10.1021/es051084k. ISSN 0013-936X. PMID 16295877.
  14. ↑ Deng, Yang; Abdel-Shafy, Hussein I. (2024). "Barriers to Ferrate(VI) Application in Water and Wastewater Treatment". Environmental Science & Technology. 58 (7): 3057–3060. doi:10.1021/acs.est.3c09203.
  15. ↑ "Russia's ready to contribute to overcoming challenges of 'global water bankruptcy' – ASI". TASS. Retrieved 2026-10-10.