Actinocene Explained

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^2-, which is) bound to an actinide-metal center (An) in the oxidation state IV, resulting in the general formula An(C₈H₈)₂.^{[1] [2]}

Characterised actinocenes

!Name!Formula!An^IV centre!First synthesis!Crystal colour !An–COT distance (Å)!Space group

Thorocene	Th(C8H8)2	Th	1969	style='background: #FFFF00'	bright yellow	2.004	P21/n
Protactinocene	Pa(C8H8)2	Pa	1974	style='background: #E9D66B'	yellowish	–	P21/n
Uranocene	U(C8H8)2	U	1968	style='background: #00A550'	deep green	1.926	P21/n
Neptunocene	Np(C8H8)2	Np	1970	style='background: #B8860B'	yellow-brown	1.909	P21/n
Plutonocene	Pu(C8H8)2	Pu	1970	style='background: #C51E3A'	dark red	1.898	I2/m

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.^[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.

Bonding

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 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).

See also

• Organoactinide chemistry
• f-block metallocene

Notes and References

1. Minasian . Stefan G. . Jason M. . Keith . New evidence for 5f covalency in actinocenes determined from carbon K-edge XAS and electronic structure theory . 2014 . . 5 . 1 . 351–359 . 10.1039/C3SC52030G.
2. Book: Greenwood. Norman N.. Chemistry of the Elements. Earnshaw. Alan. Butterworth-Heinemann. 1997. 978-0-08-037941-8. 1278–1280.
3. Seyferth . D. . Uranocene. The First Member of a New Class of Organometallic Derivatives of the f Elements . 2004 . . 23 . 15 . 3562–3583 . 10.1021/om0400705. free .
4. Goffart. J.. Fuger. J.. Brown. D.. Duyckaerts. G.. 1974-05-01. On the cyclooctatetraenyl compounds of actinide elements part II. Bis-(cyclooctatetraenyl) protactinium(IV). Inorganic and Nuclear Chemistry Letters. en. 10. 5. 413–419. 10.1016/0020-1650(74)80119-4. 0020-1650.
5. Avdeef. Alex. Raymond. Kenneth N.. Hodgson. Keith O.. Zalkin. Allan. 1972-05-01. Two isostructural actinide .pi. complexes. Crystal and molecular structure of bis(cyclooctatetraenyl)uranium(IV), U(C8H8)2, and bis(cyclooctatetraenyl)thorium(IV), Th(C8H8)2. Inorganic Chemistry. 11. 5. 1083–1088. 10.1021/ic50111a034. 0020-1669.
6. De Ridder. D. J. A.. Rebizant. J.. Apostolidis. C.. Kanellakopulos. B.. Dornberger. E.. 1996-03-15. Bis(cyclooctatetraenyl)neptunium(IV). Acta Crystallographica Section C: Crystal Structure Communications. en. 52. 3. 597–600. 10.1107/S0108270195013047. 0108-2701.
7. Windorff. Cory J.. Sperling. Joseph M.. Albrecht-Schönzart. Thomas E.. Bai. Zhuanling. Evans. William J.. Gaiser. Alyssa N.. Gaunt. Andrew J.. Goodwin. Conrad A. P.. Hobart. David E.. Huffman. Zachary K.. Huh. Daniel N.. 2020-09-21. A Single Small-Scale Plutonium Redox Reaction System Yields Three Crystallographically-Characterizable Organoplutonium Complexes. Inorganic Chemistry. en. 59. 18. 13301–13314. 10.1021/acs.inorgchem.0c01671. 32910649 . 1680020 . 221623763 . 0020-1669.
8. Apostolidis. Christos. Walter. Olaf. Vogt. Jochen. Liebing. Phil. Maron. Laurent. Edelmann. Frank T.. 2017-04-24. A Structurally Characterized Organometallic Plutonium(IV) Complex. Angewandte Chemie International Edition. en. 56. 18. 5066–5070. 10.1002/anie.201701858. 5485009. 28371148.
9. Kerridge . Andrew . f-Orbital covalency in the actinocenes (An = Th–Cm): multiconfigurational studies and topological analysis . 2014 . . 4 . 24 . 12078–12086 . 10.1039/C3RA47088A. 2014RSCAd...412078K . free .