text: *Ferrocene: bis(η-cyclopentadienyl)iron
  *Uranocene: bis(η-1,3,5,7-cyclooctatetraene)uranium
  *W(CO)(PPr)(η-H): the first compound to be synthesized with a dihydrogen ligand.
  *IrCl(CO)[P(CH)](η-O): the dioxygen derivative which forms reversibly upon oxygenation of Vaska's complex.