Phenanthroline

Phenanthroline is a heterocyclic organic compound. It can be a ligand in coordination chemistry; in this role it is abbreviated phen. Being a bidentate ligand, it is commonly used as a chelating agent for metal ions.

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

Ferroin is used as a cell permeable inhibitor for metalloproteases in cell biology.

In the related compound bathohenanthroline the 4 and 7 positions have a phenyl group.