1,10-Phenanthroline (phen) is a heterocyclic organic compound. It is a white solid that is soluble in organic solvents.  The 1,10 refer to the location of the nitrogen atoms that replace CH's in the hydrocarbon called phenanthrene.
Abbreviated "phen", it is used as a ligand in coordination chemistry, forming strong complexes with most metal ions. It is often sold as the monohydrate.