Ferroin

Ferroin
	The structure of the [Fe(o-phen)3]2+ complex cation in ferroin
Identifiers
CAS Number	14634-91-4 ;
3D model (JSmol)	Interactive image;
ChemSpider	76289 ;
ECHA InfoCard	100.035.145
PubChem CID	84567;
UNII	YP88WTW2E4 ;
CompTox Dashboard (EPA)	DTXSID00163588 ;
	InChI InChI=1S/3C12H8N2.Fe.H2O4S/c31-3-9-5-6-10-4-2-8-14-12(10)11(9)13-7-1;;1-5(2,3)4/h31-8H;;(H2,1,2,3,4)/q;;;+2;/p-2 Key: CIWXFRVOSDNDJZ-UHFFFAOYSA-L ; InChI=1/3C12H8N2.Fe.H2O4S/c31-3-9-5-6-10-4-2-8-14-12(10)11(9)13-7-1;;1-5(2,3)4/h31-8H;;(H2,1,2,3,4)/q;;;+2;/p-2 Key: CIWXFRVOSDNDJZ-NUQVWONBAU;
	SMILES [Fe+2].[O-]S([O-])(=O)=O.n3c2c1ncccc1ccc2ccc3.n3c2c1ncccc1ccc2ccc3.n1c3c(ccc1)ccc2cccnc23;
Properties
Chemical formula	C36H24FeN62+
Molar mass	596.27 g/mol
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Ferroin is the chemical compound with the formula [Fe(o-phen)₃]SO₄, where o-phen is an abbreviation for 1,10-phenanthroline, a bidentate ligand. The term "ferroin" is used loosely and includes salts of other anions such as chloride.^[1] Ferroin is one of many transition metal complexes of 1,10-phenanthroline.

Structure

Many salts of [Fe(o-phen)₃]2+ have been characterized by X-ray crystallography. The structures of [Fe(o-phen)₃]²⁺ and [Fe(o-phen)₃]³⁺ are almost identical, consistent with both being low-spin. These cations are octahedral with D₃ symmetry group. The Fe-N distances are 197.3 pm.^[2]

Preparation and reactions

Ferroin sulfate may be prepared by combining phenanthroline to ferrous sulfate in water.

3 phen + Fe²⁺ → [Fe(phen)₃]²⁺

The main reaction is 1-electron oxidation. [Fe(phen)₃]²⁺ → [Fe(phen)₃]³⁺ + 1 e⁻ Addition of sulfuric acid to an aqueous solution of [Fe(phen)₃]²⁺ causes hydrolysis:

[Fe(phen)₃]²⁺ + 3 H₂SO₄ + 6 H₂O → [Fe(OH₂)₆]²⁺ + 3 [phenH]HSO₄⁻

Redox indicator

Phenanthroline Fe(II) (Redox indicator)
E⁰= 1.06 V
Reduced.	↔	Oxidized
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This complex is used as an indicator in analytical chemistry.^[3] The active ingredient is the [Fe(o-phen)₃]²⁺ ion, which is a chromophore that can be oxidized to the ferric derivative [Fe(o-phen)₃]³⁺. The potential for this redox change is +1.06 volts in 1 M H₂SO₄. It is a popular redox indicator for visualizing oscillatory Belousov–Zhabotinsky reactions.

Ferroin is suitable as a redox indicator, as the color change is reversible, very pronounced and rapid, and the ferroin solution is stable up to 60 °C. It is the main indicator used in cerimetry.^[4]

Nitroferroin, the complex of iron(II) with 5-nitro-1,10-phenanthroline, has transition potential of +1.25 volts. It is more stable than ferroin, but in sulfuric acid with Ce⁴⁺ ion it requires significant excess of the titrant. It is however useful for titration in perchloric acid or nitric acid solution, where cerium redox potential is higher.^[4]

The redox potential of the iron-phenanthroline complex can be varied between +0.84 V and +1.10 V by adjusting the position and number of methyl groups on the phenanthroline core.^[4]

Related complexes

References

^ Sattar, Simeen (2011). "A Unified Kinetics and Equilibrium Experiment: Rate Law, Activation Energy, and Equilibrium Constant for the Dissociation of Ferroin". Journal of Chemical Education. 88 (4): 457–460. Bibcode:2011JChEd..88..457S. doi:10.1021/ed100797s.
^ Baker, Joe; Engelhardt, Lutz M.; Figgis, Brian N.; White, Allan H. (1975). "Crystal Structure, Electron Spin Resonance, and Magnetism of Tris(o-Phenanthroline)Iron(III) Perchlorate Hydrate". Journal of the Chemical Society, Dalton Transactions (6): 530. doi:10.1039/DT9750000530.
^ Harris, D. C. (1995). Quantitative Chemical Analysis (4th ed.). New York, NY: W. H. Freeman. ISBN 978-0-7167-2508-4.
^ ^a ^b ^c Handbook on the Physics and Chemistry of Rare Earths. Elsevier. 2006. pp. 289–. ISBN 978-0-08-046672-9.

[1] Sattar, Simeen (2011). "A Unified Kinetics and Equilibrium Experiment: Rate Law, Activation Energy, and Equilibrium Constant for the Dissociation of Ferroin". Journal of Chemical Education. 88 (4): 457–460. Bibcode:2011JChEd..88..457S. doi:10.1021/ed100797s.

[2] Baker, Joe; Engelhardt, Lutz M.; Figgis, Brian N.; White, Allan H. (1975). "Crystal Structure, Electron Spin Resonance, and Magnetism of Tris(o-Phenanthroline)Iron(III) Perchlorate Hydrate". Journal of the Chemical Society, Dalton Transactions (6): 530. doi:10.1039/DT9750000530.

[3] Harris, D. C. (1995). Quantitative Chemical Analysis (4th ed.). New York, NY: W. H. Freeman. ISBN 978-0-7167-2508-4.

[physchemrare-4] Handbook on the Physics and Chemistry of Rare Earths. Elsevier. 2006. pp. 289–. ISBN 978-0-08-046672-9.

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