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 (COT2-, which is C
8
H2−
8
) bound to an actinide-metal center (An) in the oxidation state IV, resulting in the general formula An(C8H8)2.[1][2]

Uranocene molecular representations showing the U atom sandwiched between 2 COT2- ligands

Characterised actinocenes

More information Name, Formula ...
Name Formula AnIV centre First synthesis Crystal colour An–COT distance (Å) Space group
Thorocene Th(C8H8)2 Th 1969 bright yellow 2.004 P21/n
Protactinocene Pa(C8H8)2 Pa 1974 yellowish P21/n
Uranocene U(C8H8)2 U 1968 deep green 1.926 P21/n
Neptunocene Np(C8H8)2 Np 1970 yellow-brown 1.909 P21/n
Plutonocene Pu(C8H8)2 Pu 1970 dark red 1.898 I2/m
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The most studied actinocene is uranocene, U(C8H8)2, which in 1968 was the first member of this family to be synthesised and is still viewed as the archetypal example.[2][3] Other actinocenes that have been synthesised are protactinocene[4] (Pa(C8H8)2), thorocene[5] (Th(C8H8)2), neptunocene[6] (Np(C8H8)2), and plutonocene[7][8] (Pu(C8H8)2). Especially the latter two, neptunocene and plutonocene, have not been extensively studied experimentally since the 1980s because of the radiation hazard they pose.[7][8]

Bonding

The actinide-cyclooctatetraenyl bonding has been of interest for multiple theoretical studies.[8][9] Computational chemistry methods indicate bonding with a large covalent character resulting mainly from the mixing of actinide 6d orbitals with ligand π-orbitals, with a smaller interaction involving the actinide 5f and ligand π-orbitals.[9] The covalent component is characterised by donation of electron density to the actinide.

Analogous sandwiched M(C8H8)2 compounds also exist for lanthanides M = Nd, Tb, and Yb, but therein the bonding is mostly ionic rather than covalent (see lanthanocenes).[3]

See also

References

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