Ferroin

Ferroin
Identifiers
CAS Number	14634-91-4 ;
3D model (JSmol)	Interactive image;
ChemSpider	76289 ;
ECHA InfoCard	100.035.145
PubChem CID	84567;
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).
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	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]

Redox indicator

Phenanthroline Fe(II) (Redox indicator)
E⁰= 1.06 V
Reduced.	↔	Oxidized

This coordination compound is used as an indicator in analytical chemistry.[2] 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.[3]

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.[3]

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.[3]

Preparation

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

3 phen + Fe²⁺ → [Fe(phen)₃]²⁺

The iron is low spin and octahedral with D₃ symmetry. The intense color of this ferrous complex arises from a metal-to-ligand charge-transfer transition.

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.
Harris, D. C. (1995). Quantitative Chemical Analysis (4th ed.). New York, NY: W. H. Freeman. ISBN 978-0-7167-2508-4.
Handbook on the Physics and Chemistry of Rare Earths. Elsevier. 2006. pp. 289–. ISBN 978-0-08-046672-9.

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

[physchemrare-3] Handbook on the Physics and Chemistry of Rare Earths. Elsevier. 2006. pp. 289–. ISBN 978-0-08-046672-9.