A macrocycle is, as defined by IUPAC, "a cyclic macromolecule or a macromolecular cyclic portion of a molecule." In the chemical literature, organic chemists may consider any molecule containing a ring of seven, fifteen, or any arbitrarily large number of atoms to be macrocyclic. Generally however, when speaking of macrocycles, coordination chemists define a macrocycle as a cyclic molecule with three or more potential donor atoms in a ring of at least nine atoms.