C5H5nM
C5H5nM refers to a class of organometallic compounds where a cyclopentadienyl anion (C5H5-) is bonded to a metal (M) in a specific oxidation state (n). The cyclopentadienyl anion is a five-membered ring of carbon atoms with a delocalized pi electron system, giving it aromatic character. This aromaticity makes it a very stable ligand, capable of forming strong bonds with a wide variety of metal atoms.
The 'n' in C5H5nM represents the oxidation state of the metal. For example, in ferrocene, the iron
The bonding between the metal and the cyclopentadienyl ring is typically described as a combination of ionic