Ferroin

Ferroin

Identifiers
CAS Number	14634-91-4 Y
3D model (JSmol)	Interactive image
ChemSpider	76289 Y
ECHA InfoCard	100.035.145
PubChem CID	84567
InChI InChI=1S/3C12H8N2.Fe.H2O4S/c3*1-3-9-5-6-10-4-2-8-14-12(10)11(9)13-7-1;;1-5(2,3)4/h3*1-8H;;(H2,1,2,3,4)/q;;;+2;/p-2 Y Key: CIWXFRVOSDNDJZ-UHFFFAOYSA-L Y InChI=1/3C12H8N2.Fe.H2O4S/c3*1-3-9-5-6-10-4-2-8-14-12(10)11(9)13-7-1;;1-5(2,3)4/h3*1-8H;;(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).
Y  (what is YN ?)
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.

This coordination compound is used as an indicator in analytical chemistry. 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 making oscillatory Belousov–Zhabotinsky reactions visible.

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.

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.

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

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

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.