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CAS number 66-71-7 YesY
ChemSpider 1278 YesY
DrugBank DB02365
ChEBI CHEBI:44975 YesY
RTECS number SF8300000
Jmol-3D images Image 1
Molecular formula C12H8N2
Molar mass 180.21 g/mol
Appearance colourless crystals
Density 1.31 g/cm3
Melting point

117 °C, 390 K, 243 °F

Solubility in water moderate
Solubility in other solvents acetone


R-phrases R25, R50/53
S-phrases S45,S60,S61
Main hazards mild neurotoxin, strong nephrotoxin, and powerful diuretic
Related compounds
Related compounds 2,2'-bipyridine
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Phenanthroline (phen) is a heterocyclic organic compound. It is a white solid that is soluble in organic solvents. It is used as a ligand in coordination chemistry, it forms strong complexes with most metal ions.[1] In terms of its coordination properties, phen is similar to 2,2'-bipyridine (bipy).


Phenanthroline may be prepared by two successive Skraup reactions of glycerol with o-phenylenediamine, catalyzed by sulfuric acid, and an oxidizing agent, traditionally aqueous arsenic acid or nitrobenzene.[2] Dehydration of glycerol gives acrolein which condenses with the amine followed by a cyclization.

Peptidase inhibitor

1,10-Phenanthroline is an inhibitor of metallopeptidases, with one of the first observed instances reported in carboxypeptidase A.[3] Inhibition of the enzyme occurs by removal and chelation of the metal ion required for catalytic activity, leaving an inactive apoenzyme. 1,10-Phenanthroline targets mainly zinc metallopeptidases, with a much lower affinity for calcium.[4]

Ferroin and analogues

The complex [Fe(phen)3]2+, called "ferroin," is used for the photometric determination of Fe(II).[5] It is used as a redox indicator with standard potential +1.06 V. The reduced ferrous form has a deep red colour and the oxidised form is light-blue.[6] Ferroin is used as a cell permeable inhibitor for metalloproteases in cell biology.

The pink complex [Ni(phen)3]2+ has been resolved into its Δ and Λ isomers.[7] The analogous [Ru(phen)3]2+ has long been known to be bioactive.[8]

Related phen ligands

A variety of substituted derivatives of phen have been examined as ligands. Neocuproine, 2,9-dimethyl-1,10-phenanthroline, is a bulky ligand. In "bathophenanthroline," the 4 and 7 positions are substituted by phenyl groups. The more electron-rich phenanthroline ligand is 3,4,7,8-tetramethyl-1,10-phenanthroline.[1]

As an indicator for alkyllithium reagents

Alkyllithium reagents form deeply colored derivatives with phenanthroline. The alkyllithium content of solutions can be determined by treatment of such reagents with small amounts of phenanthroline (ca. 1 mg) followed by titration with alcohols to a colourless endpoint.[9]

Grignard reagents may be similarly titrated.[10]


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