Organometallic coordination compounds in which one atom of a transition metal such as iron, ruthenium or osmium is bonded to and only to the face of two cyclopentadienyl [![[hapto]](/img5/8_files/ETA.gif)
5-(C5H5)] ligands which lie in parallel planes. NOC Rule D-2.55. The term should not be used for analogues having rings other than cyclopentadienyl as ligands.
