ferrocene, the earliest and best known of the so-called sandwich compounds; these are derivatives of transition metals in which two organic ring systems are bonded symmetrically to the metal atom. Its molecular formula is (C5H5)2Fe.
First prepared in 1951 by the reaction of sodium cyclopentadienide with iron(+2) chloride, ferrocene occurs as highly stable orange crystals with a melting point of 174° C (345° F). Chemically, ferrocene behaves like benzene and other aromatic compounds in that it undergoes substitution reactions. The removal of one electron from the molecule raises the iron atom to the next-higher oxidation state (i.e., from +2 to +3), leading to the formation of salts containing the blue ferricinium cation, (C5H5)2Fe+.