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Sample of 1,10-Phenanthroline
Preferred IUPAC name
  • 66-71-7 checkY
  • monohydrate: 5144-89-8 (monohydrate) checkY
3D model (JSmol)
ECHA InfoCard 100.000.572 Edit this at Wikidata
EC Number
  • 200-629-2
  • monohydrate: 627-114-9
RTECS number
  • SF8300000
UN number 2811
  • InChI=1S/C12H8N2/c1-3-9-5-6-10-4-2-8-14-12(10)11(9)13-7-1/h1-8H checkY
  • InChI=1/C12H8N2/c1-3-9-5-6-10-4-2-8-14-12(10)11(9)13-7-1/h1-8H
  • c1cc2ccc3cccnc3c2nc1
  • monohydrate: C1=CC2=C(C3=C(C=CC=N3)C=C2)N=C1.O
Molar mass 180.21 g/mol
Appearance colourless crystals
Density 1.31 g/cm3
Melting point 118.56 °C (245.41 °F; 391.71 K)[2]
Boiling point 409.2 [2]
Solubility in other solvents acetone, ethanol[2]
Acidity (pKa) 4.84 (phenH+)[3]
Main hazards mild neurotoxin, strong nephrotoxin, and powerful diuretic
GHS pictograms GHS06: ToxicGHS09: Environmental hazard
GHS Signal word Danger
H301, H410
P264, P270, P273, P301+P310, P321, P330, P391, P405, P501
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, forming strong complexes with most metal ions.[4][5] It is often sold as the monohydrate.


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

Coordination chemistry

In terms of its coordination properties, phenanthroline is similar to 2,2'-bipyridine (bipy) but binds metals more tightly since the chelating nitrogen donors are preorganized. Phenanthroline is however a weaker donor than bipy.[7]

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).[8] 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.[9] The pink complex [Ni(phen)3]2+ has been resolved into its Δ and Λ isomers.[10] Copper(I) forms [Cu(phen)2]+, which is luminescent.[11][12]

Bioinorganic chemistry

The ferroin analogue [Ru(phen)3]2+ has long been known to be bioactive.[13]

1,10-Phenanthroline is an inhibitor of metallopeptidases, with one of the first observed instances reported in carboxypeptidase A.[14] 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.[15]

Related phen ligands

A variety of substituted derivatives of phen have been examined as ligands.[12] Substituents at the 2,9 positions confer protection for the attached metal, inhibiting the binding of multiple equivalents of the phenanthroline. Phen itself form complexes of the type [M(phen)3]Cl2 when treated with metal dihalides (M = Fe, Co, Ni). By contrast, neocuproine and bathocuproine form 1:1 complexes such as [Ni(neo/batho-cuproine)Cl2]2.[16]

Basicities of 1,10-Phenanthrolines and 2,2'-Bipyridine[17]
ligand pKa comment/alt. name illustration
1,10-phenanthroline 4.86 phen
Numbering for 1,10-phenanthroline derivatives.
2,2'-bipyridine 4.30 less basic than phen
5-nitro-1,10-phenanthroline 3.57
2,9-dimethyl-1,10-phenanthroline unknown neocuproine
4,7-dimethyl-1,10-phenanthroline 5.97
4,7-diphenyl-1,10-phenanthroline unknown bathophenanthroline
5,6-dimethyl-1,10-phenanthroline 5.20
3,4,7,8-tetramethylphenanthroline 6.31 3,4,7,8-Me4phen
4,7-dimethoxy-1,10‐phenanthroline 6.45 4,7-(MeO)2phen[18]

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.[19] Grignard reagents may be similarly titrated.[20]

See also

  • Ferroin – Complex of Fe2+ by ortho-phenantroline


  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. ^ a b c d Haynes, p. 3.444
  3. ^ Haynes, p. 5.95
  4. ^ Luman, C.R. and Castellano, F.N. (2003) "Phenanthroline Ligands" in Comprehensive Coordination Chemistry II. Elsevier. ISBN 978-0-08-043748-4.
  5. ^ Sammes, Peter G.; Yahioglu, Gokhan (1994). "1,10-Phenanthroline: A versatile ligand". Chemical Society Reviews. 23 (5): 327. doi:10.1039/cs9942300327.
  6. ^ Halcrow, Barbara E.; Kermack, William O. (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. PMID 20983293.
  7. ^ Teng, Qiaoqiao; Huynh, Han Vinh (2017). "A unified ligand electronic parameter based on C NMR spectroscopy of N-heterocyclic carbene complexes". Dalton Transactions. 46 (3): 614–627. doi:10.1039/C6DT04222H. PMID 27924321.
  8. ^ Belcher R (1973). "Application of chelate Compounds in Analytical Chemistry". Pure and Applied Chemistry. 34: 13–27. doi:10.1351/pac197334010013. S2CID 44054260.
  9. ^ 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 (9): 3968–3970. doi:10.1021/ic902554b. PMID 20415494.
  10. ^ George B. Kauffman; Lloyd T. Takahashi (1966). Resolution of the tris-(1,10-Phenanthroline)Nickel(II) Ion. Inorg. Synth. Inorganic Syntheses. 5. pp. 227–232. doi:10.1002/9780470132395.ch60. ISBN 9780470132395.
  11. ^ Armaroli N (2001). "Photoactive Mono- and Polynuclear Cu(I)-Phenanthrolines. A Viable Alternative to Ru(Ii)-Polypyridines?". Chemical Society Reviews. 30 (2): 113–124. doi:10.1039/b000703j.
  12. ^ a b Pallenberg A. J.; Koenig K. S.; Barnhart D. M. (1995). "Synthesis and Characterization of Some Copper(I) Phenanthroline Complexes". Inorg. Chemistry. 34 (11): 2833–2840. doi:10.1021/ic00115a009.
  13. ^ Dwyer, F. P.; Gyarfas, Eleonora C.; Rogers, W. P.; Koch, Judith H. (1952). "Biological Activity of Complex Ions". Nature. 170 (4318): 190–191. Bibcode:1952Natur.170..190D. doi:10.1038/170190a0. PMID 12982853. S2CID 6483735.
  14. ^ Felber, Jean-Pierre; Coombs, Thomas L.; Vallee, Bert L. (1962). "The mechanism of inhibition of carboxypeptidase A by 1,10-phenanthroline". Biochemistry. 1 (2): 231–238. doi:10.1021/bi00908a006. PMID 13892106.
  15. ^ Salvesen, GS & Nagase, H (2001). "Inhibition of proteolytic enzymes". In Beynon, Rob & Bond, J S (eds.). Proteolytic Enzymes: A Practical Approach. 1 (2nd ed.). Oxford University Press. pp. 105–130. ISBN 9780199636624.
  16. ^ Preston, H. S.; Kennard, C. H. L. (1969). "Crystal Structure of di-mu-Chloro-sym-trans-Dichloro-Bis-(2,9-Dimethyl-1,10-Phenanthroline)dinickel(II)-2-Chloroform". J. Chem. Soc. A: 2682–2685. doi:10.1039/J19690002682.
  17. ^ Leipoldt, J.G.; Lamprecht, G.J.; Steynberg, E.C. (1991). "Kinetics of the substitution of acetylacetone in acetylactonato-1,5-cyclooctadienerhodium(I) by derivatives of 1,10-phenantrholine and 2,2′-dipyridyl". Journal of Organometallic Chemistry. 402 (2): 259–263. doi:10.1016/0022-328X(91)83069-G.
  18. ^ Altman, Ryan A. (2008). "1,10-Phenanthroline, 4,7-Dimethoxy". Encyclopedia of Reagents for Organic Synthesis. eEROS. doi:10.1002/047084289X.rn00918. ISBN 978-0471936237.
  19. ^ Fagan, Paul J.; Nugent, William A. (1998). "1-Phenyl-2,3,4,5-Tetramethylphosphole". Organic Syntheses.; Collective Volume, 9, p. 653
  20. ^ Lin, Ho-Shen; Paquette, Leo A. (1994). "A Convenient Method for Determining the Concentration of Grignard Reagents". Synth. Commun. 24 (17): 2503–2506. doi:10.1080/00397919408010560.

Cited sources