Sandwich Complexes

A sandwich compound is an organic substance that consists of two arene (ring) ligands and a metal connected by haptic, covalent connections. Substituted derivatives and heterocyclic derivatives of arenes all share the formula CnHn. It is called "sandwiched" because the metal is often sandwiched between the two rings. The metallocenes are a unique subclass of sandwich complexes. In a 1956 paper, J. D. Dunitz, L. E. Orgel, and R. A. Rich established the structure of ferrocene using X-ray crystallography, and used this information to coin the phrase "sandwich compound" in organometallic nomenclature. Robert Burns Woodward and Ernst Otto Fischer each independently predicted the proper structure some years prior, which calls for the molecule to include one iron atom squished between two parallel cyclopentadienyl rings.