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Sample of 1,10-Phenanthroline
Preferred IUPAC name
3D model (JSmol)
ECHA InfoCard 100.000.572
RTECS number SF8300000
Molar mass 180.21 g/mol
Appearance colourless crystals
Density 1.31 g/cm3
Melting point 117 °C (243 °F; 390 K)
Solubility in other solvents acetone


Acidity (pKa) 4.86 (phenH+)[2]
Main hazards mild neurotoxin, strong nephrotoxin, and powerful diuretic
R-phrases (outdated) R25, R50/53
S-phrases (outdated) S45,S60,S61
Related compounds
Related compounds
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

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.[3]


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.[4] Dehydration of glycerol gives acrolein which condenses with the amine followed by a cyclization.

Coordination chemistry[edit]

In terms of its coordination properties, phen is similar to 2,2'-bipyridine (bipy) but binds metals more tightly since the chelating nitrogen donors are preorganized.

Many homoleptic complexes are known. Particularly well studied is [Fe(phen)3]2+, called "ferroin." It was 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] The pink complex [Ni(phen)3]2+ has been resolved into its Δ and Λ isomers.[7] Copper(I) forms [Cu(phen)2]+, which is luminescent.[8][9]

Bioinorganic chemistry[edit]

The ferroin analogue [Ru(phen)3]2+ has long been known to be bioactive.[10]

1,10-Phenanthroline is an inhibitor of metallopeptidases, with one of the first observed instances reported in carboxypeptidase A.[11] 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.[12]

Related phen ligands[edit]

A variety of substituted derivatives of phen have been examined as ligands.[9] 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.[3]

Numbering for 1,10-phenanthroline derivatives.

As an indicator for alkyllithium reagents[edit]

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.[13] Grignard reagents may be similarly titrated.[14]


  1. ^ Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 211. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4. 
  2. ^ Durand, J., et al., "Long-Lived Palladium Catalysts for Co/Vinyl Arene Polyketones Synthesis: A Solution to Deactivation Problems", Chemistry – A European Journal 2006, volume 12, 7639-7651. doi:10.1002/chem.200501047
  3. ^ a b C.R. Luman, F.N. Castellano "Phenanthroline Ligands" in Comprehensive Coordination Chemistry II, 2003, Elsevier. ISBN 978-0-08-043748-4.
  4. ^ B. E. Halcrow; W. O. Kermack (1946). "43. Attempts to find new antimalarials. Part XXIV. Derivatives of o-phenanthroline (7 : 8 : 3′ : 2′-pyridoquinoline)". J. Chem. Soc.: 155–157. doi:10.1039/jr9460000155. 
  5. ^ Belcher, R. "Application of chelate Compounds in Analytical Chemistry" Pure and Applied Chemistry, 1973, volume 34, pages 13-27.
  6. ^ Bellér, G. B.; Lente, G. B.; Fábián, I. N. (2010). "Central Role of Phenanthroline Mono-N-oxide in the Decomposition Reactions of Tris(1,10-phenanthroline)iron(II) and -iron(III) Complexes". Inorganic Chemistry. 49: 3968–3970. doi:10.1021/ic902554b. PMID 20415494. 
  7. ^ George B. Kauffman, Lloyd T. Takahashi (1966). "Resolution of the tris-(1,10-Phenanthroline)Nickel(II) Ion". Inorg. Synth. 5: 227–232. doi:10.1002/9780470132395.ch60. 
  8. ^ Armaroli, N., "Photoactive Mono- and Polynuclear Cu(I)-Phenanthrolines. A Viable Alternative to Ru(Ii)-Polypyridines?", Chemical Society Reviews 2001, volume 30, 113-124.doi:10.1039/b000703j
  9. ^ a b Pallenberg, A. J.; Koenig, K. S.; Barnhart, D. M., "Synthesis and Characterization of Some Copper(I) Phenanthroline Complexes", Inorg. Chemistry 1995, volume 34, 2833-2840. doi:10.1021/ic00115a009
  10. ^ F. P. Dwyer; E. C. Gyarfas; W. P. Rogers; J. H. Koch (1952). "Biological Activity of Complex Ions". Nature. 170 (4318): 190–191. doi:10.1038/170190a0. PMID 12982853. 
  11. ^ Felber, JP, Coombs, TL & Vallee, BL (1962). "The mechanism of inhibition of carboxypeptidase A by 1,10-phenanthroline". Biochemistry. 1 (2): 231–238. doi:10.1021/bi00908a006. PMID 13892106. 
  12. ^ Salvesen, GS & Nagase, H (2001). "Inhibition of proteolytic enzymes". Proteolytic enzymes: a practical approach, 2 edn. 1: 105–130. 
  13. ^ Paul J. Fagan and William A. Nugent (1998). "1-Phenyl-2,3,4,5-Tetramethylphosphole". Organic Syntheses. ; Collective Volume, 9, p. 653 
  14. ^ Ho-Shen Lin; Leo A. Paquette (1994). "A Convenient Method for Determining the Concentration of Grignard Reagents". Synth. Commun. 24 (17): 2503–2506. doi:10.1080/00397919408010560.