Actinocenes are a family of organoactinide compounds consisting of metallocenes containing elements from the actinide series. They typically have a sandwich structure with two dianionic cyclooctatetraenyl ligands (COT<sup>2âÂÂ</sup>, which is ) bound to an actinide-metal center (An) in the oxidation state IV, resulting in the general formula An(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>.
The most studied actinocene is uranocene, U(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>, which in 1968 was the first member of this family to be synthesised and is still viewed as the archetypal example. Other actinocenes that have been synthesised are protactinocene (Pa(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>), thorocene (Th(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>), neptunocene (Np(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>), and plutonocene (Pu(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>). Especially the latter two, neptunocene and plutonocene, have not been extensively studied experimentally since the 1980s because of the radiation hazard they pose. Berkelocene (with a modified COT ligand) was synthesised in 2025, the first actinocene with a new actinide in over 50 years.
The actinide-cyclooctatetraenyl bonding has been of interest for multiple theoretical studies. Computational chemistry methods indicate bonding with a large covalent character resulting mainly from the mixing of actinide 6d orbitals with ligand ÃÂ-orbitals, with a smaller interaction involving the actinide 5f and ligand ÃÂ-orbitals. The covalent component is characterised by donation of electron density to the actinide. This donation is notably reduced in berkelocene relative to other characterized actinocenes, due to the stable 5f<sup>7</sup> electron configuration of Bk<sup>4+</sup>.
Analogous sandwiched M(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub> compounds also exist for lanthanides M = Nd, Tb, and Yb, but therein the bonding is mostly ionic rather than covalent (see lanthanocenes).