Uranocene
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| Names | |||
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IUPAC name
Bis(η8-cyclooctatetraenyl)uranium(IV)
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| Other names
Uranium cyclooctatetraenide
U(COT)2 |
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| Identifiers | |||
11079-26-8 
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| 3D model (Jmol) | Interactive image | ||
| ChemSpider |
57575622 
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| Properties | |||
| C16H16U | |||
| Molar mass | 446.33 g/mol | ||
| Appearance | green crystals | ||
| Hazards | |||
| Main hazards | ignites in air | ||
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 (what is ?) |
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| Infobox references | |||
Uranocene, U(C8H8)2, is an organouranium compound composed of a uranium atom sandwiched between two cyclooctatetraenide rings. It was one of the first organouranium compounds to be synthesized. It is a green air-sensitive solid that dissolves in organic solvents. Uranocene, a member of the "actinocenes," a group of metallocenes incorporating elements from the actinide series. It is the most studied bis[8]annulene-metal system, although it has no practical applications.
Uranocene was first described in 1968, when it was prepared by the reaction of dipotassium cyclooctatetraenide and uranium tetrachloride in THF at 0°C:
Uranocene is highly reactive toward oxygen, being pyrophoric in air but stable to hydrolysis. Considering the molecule to be U4+(C8H82−)2, the η8-cyclooctatetraenide groups are planar, as expected for a ring containing 10 π-electrons, and are mutually parallel, forming a sandwich containing the uranium atom. In the solid state, the rings are eclipsed, conferring D8h symmetry on the molecule. In solution the rings rotate with a low energy barrier.
The uranium-cyclooctatetraenyl bonding was shown by photoelectron spectroscopy to be primarily due to mixing of uranium 6d orbitals into ligand pi orbitals and therefore donation of electronic charge to the uranium, with a smaller such interaction involving the uranium (5f)2 orbitals. Electronic theory calculations agree with this result and point out that the weaker interaction of the open-shell 5f orbitals with the ligand orbitals determines |MJ|, the magnitude of the angular momentum quantum number along the 8-fold symmetry axis of the ground state.
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