Plutonocene

Last updated
Plutonocene
Plutonocene.jpg
Neptunocene-from-xtal-3D-balls.png
Names
IUPAC name
Bis(η8-cyclooctatetraene)plutonium [1]
Other names
Plutonium cyclooctatetraenide
Pu(COT)2
Identifiers
3D model (JSmol)
PubChem CID
  • InChI=1S/2C8H8.Pu/c2*1-2-4-6-8-7-5-3-1;/h2*1-8H;/b2*2-1-,3-1-,4-2-,5-3-,6-4-,7-5-,8-6-,8-7-;
    Key: DFMONSHXBOWXGP-OGVMWVNQSA-N
  • c1=c[cH-]c=c[cH-]c=c1.[Pu+4].c1=c[cH-]c=c[cH-]c=c1
Properties
C16H16Pu
Molar mass 452 g·mol−1
Appearancecherry red crystals
insoluble, does not react with water
Solubility in chlorocarbonssparingly soluble (ca. 0.5 g/L)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
radiation hazard, pyrophoric, toxic
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Plutonocene, Pu(C8H8)2, is an organoplutonium compound composed of a plutonium atom sandwiched between two cyclooctatetraenide (COT2-) rings. It is a dark red, very air-sensitive solid that is sparingly soluble in toluene and chlorocarbons. [2] [3] Plutonocene is a member of the actinocene family of metallocenes incorporating actinide elements in the +4 oxidation state.

Contents

Compared to other actinocenes such as uranocene, plutonocene has been studied to a lesser degree since the 1980s due to the notable radiation hazard posed by the compound. [4] [5] Instead, it has mostly been the subject of theoretical studies relating to the bonding in the molecule. [5] [6]

Structure and bonding

The compound has been structurally characterised by single crystal XRD. [4] [5] The cyclooctatetraenide rings are eclipsed and assume a planar conformation with 8 equivalent C–C bonds of 1.41 Å length; the molecule possesses a centre of inversion at the position occupied by the plutonium atom. [4] [5] The Pu–COT distance (to the ring centroid) is 1.90 Å and the individual Pu–C distances are in the 2.63–2.64 Å range. [4]

Despite the similarity in molecular structures, plutonocene crystals are not isomorphous to other actinocenes, as plutonocene crystallises in the monoclinic I2/m space group whereas thorocene, protactinocene, uranocene and neptunocene all crystallise as monoclinic P21/n. [4]

Theoretical calculations utilising various computational chemistry methods support the existence of an enhanced covalent character in plutonocene from the interaction of Pu 6d and 5f atomic orbitals with ligand-based π orbitals. [3] [5] [6]

Synthesis

Plutonocene was first synthesized in 1970 form the reaction of tetraethylammonium hexachloroplutonate(IV) ([N(C2H5)4]2PuCl6) with dipotassium cyclooctatetraenide (K2(C8H8)) in THF at room temperature: [2] [3]

(NEt4)2PuCl6 + 2 K2(C8H8) → Pu(C8H8)2 + 2 NEt4Cl + 4 KCl

This approach is different compared to the synthesis of other actinocenes which usually involves the reaction of the actinide tetrachloride AnCl4 with K2(C8H8); this is not possible in the case of plutonium, as no stable plutonium(IV) chloride species is known. [5] The reaction also does not work when using the caesium or pyridinium hexachloroplutonate(IV) salts in the place of the tetraethylammonium one. [2]

A more recent synthesis involves 1 e− oxidation of the green [K(crypt)][PuIII(C8H8)2] salt with AgI: [4]

[PuIII(C8H8)2]− + AgI → Pu(C8H8)2 + Ag0 + I−

The [PuIII(C8H8)2]− anion is obtained via ligand substitution from K2(C8H8) and other organoplutonium(III) complexes, which can be ultimately derived from reduction of the more common PuO2 with HBr in THF. [4] PuIII halides PuCl3 and PuI3 have also been used as the plutonium starting material. [4] [5]

Other properties

The product is chemically analogous to uranocene and neptunocene, and they practically exhibit identical chemical reactivity. All three compounds are insensitive to water or dilute aqueous base, but are air-sensitive and react quickly to form oxides. [2] [3] [4] They are only slightly soluble (with saturation concentrations of about 10−3 M) in aromatic or chlorinated solvents such as benzene, toluene, carbon tetrachloride or chloroform. [2] [3]

References

  1. ↑ Nomenclature of inorganic chemistry - UPAC Recommendations 2005
  2. 1 2 3 4 5 Karraker, David G.; Stone, John Austin; Jones, Erwin Rudolph; Edelstein, Norman (1970-08-01). "Bis(cyclooctatetraenyl)neptunium(IV) and bis(cyclooctatetraenyl)plutonium(IV)" . Journal of the American Chemical Society. 92 (16): 4841–4845. doi:10.1021/ja00719a014. ISSN   0002-7863.
  3. 1 2 3 4 5 Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Boston, Mass.: Butterworth-Heinemann. pp. 1278–1280. ISBN   978-0-08-037941-8.
  4. 1 2 3 4 5 6 7 8 9 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. 59 (18): 13301–13314. doi:10.1021/acs.inorgchem.0c01671. ISSN   0020-1669. OSTI   1680020. PMID   32910649. S2CID   221623763.
  5. 1 2 3 4 5 6 7 Apostolidis, Christos; Walter, Olaf; Vogt, Jochen; Liebing, Phil; Maron, Laurent; Edelmann, Frank T. (2017). "A Structurally Characterized Organometallic Plutonium(IV) Complex". Angewandte Chemie International Edition. 56 (18): 5066–5070. doi:10.1002/anie.201701858. ISSN   1521-3773. PMC   5485009 . PMID   28371148.
  6. 1 2 Kerridge, Andrew (2013-11-06). "Oxidation state and covalency in f-element metallocenes (M = Ce, Th, Pu): a combined CASSCF and topological study". Dalton Transactions. 42 (46): 16428–16436. doi: 10.1039/C3DT52279B . ISSN   1477-9234. PMID   24072035.
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