Page "Metallocene" Paragraph 5

The general name metallocene is derived from ferrocene, ( C < sub > 5 </ sub > H < sub > 5 </ sub >)< sub > 2 </ sub > Fe or Cp < sub > 2 </ sub > Fe, systematically named bis ( η < sup > 5 </ sup >- cyclopentadienyl ) iron ( II ).

According to the IUPAC definition, a metallocene contains a transition metal and two cyclopentadienyl ligands coordinated in a sandwich structure, i. e., the two cyclopentadienyl anions are co-planar with equal bond lengths and strengths.

Using the nomenclature of " hapticity ", the equivalent bonding of all 5 carbon atoms of a cyclopentadienyl ring is denoted as η < sup > 5 </ sup >, pronounced " pentahapto.

" There are exceptions, such as uranocene, which has two cyclooctatetraene rings sandwiching a uranium atom.