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Identifiers | |
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3D model (
JSmol)
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ChemSpider | |
ECHA InfoCard | 100.035.145 |
PubChem
CID
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UNII | |
CompTox Dashboard (
EPA)
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Properties | |
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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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]
Many salts of [Fe(o-phen)3]2+ have been characterized by X-ray crystallography. The structures of [Fe(o-phen)32+ and [Fe(o-phen)33+ 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]
Ferroin sulfate may be prepared by combining phenanthroline to ferrous sulfate in water.
The main reaction is 1-electron oxidation. [Fe(phen)32+ → [Fe(phen)33+ + 1 e− Addition of sulfuric acid to an aqueous solution of [Fe(phen)32+ causes hydrolysis:
Phenanthroline Fe(II) ( Redox indicator) | ||
E0= 1.06 V | ||
Reduced. | ↔ | Oxidized |
This complex is used as an indicator in analytical chemistry. [3] The active ingredient is the [Fe(o-phen)32+ ion, which is a chromophore that can be oxidized to the ferric derivative [Fe(o-phen)33+. 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]