E3u states. Analogous compounds Analogous compounds of the form M(C8H8)2 exist for M = (Nd, Tb, Yb, Th, Pa, Np, and Pu). Extensions include the air-stable derivative U(C8H4Ph4)2 and the cycloheptatrienyl species [U(C7H7)2]−. In contrast, bis(cyclooctatetraene)iron has a very different structure, with one each of a η6- and η4-C8H8 ligands. References Further reading The f elements, Nikolas Kaltsoyannis and Peter Scott. Chemistry of the Elements, N. N. Greenwood and A. Earnshaw. Lanthanides & Actinides: Organoactinides Organouranium compounds Metallocenes Uranium(IV) compounds Substances discovered in the 1960s