C5H5- is the chemical formula for the cyclopentadienyl anion, a negatively charged ion derived from cyclopentadiene. It consists of five carbon atoms arranged in a ring, with four of the carbons participating in double bonds, giving it a unique structure. The anion is often represented as C5H5^- and is known for its stability and resonance, which allows it to delocalize its negative charge across the ring. This anion plays a significant role in organometallic chemistry, particularly in the formation of complexes with transition metals. One well-known example is the ferrocene compound, where the cyclopentadienyl anion coordinates with iron, showcasing its importance in various chemical reactions and applications.