Plutonocene

Last updated
Plutonocene
Plutonocene.jpg
Neptunocene-from-xtal-3D-balls.png
Names
IUPAC name
Bis(η8-cyclooctatetraenyl)plutonium(IV)
Other names
Plutonium cyclooctatetraenide
Pu(COT)2
Identifiers
3D model (JSmol)
  • 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. [1] [2] 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. [3] [4] Instead, it has mostly been the subject of theoretical studies relating to the bonding in the molecule. [4] [5]

Structure and bonding

The compound has been structurally characterised by single crystal XRD. [3] [4] 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. [3] [4] 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. [3]

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. [3]

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. [2] [4] [5]

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: [1] [2]

(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. [4] The reaction also does not work when using the caesium or pyridinium hexachloroplutonate(IV) salts in the place of the tetraethylammonium one. [1]

A more recent synthesis involves 1 e oxidation of the green [K(crypt)][PuIII(C8H8)2] salt with AgI: [3]

[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. [3] PuIII halides PuCl3 and PuI3 have also been used as the plutonium starting material. [3] [4]

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. [1] [2] [3] 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. [1] [2]

Related Research Articles

The actinide or actinoid series encompasses at least the 14 metallic chemical elements in the 5f series, with atomic numbers from 89 to 102, actinium through nobelium. The actinide series derives its name from the first element in the series, actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide.

<span class="mw-page-title-main">Curium</span> Chemical element, symbol Cm and atomic number 96

Curium is a synthetic chemical element; it has symbol Cm and atomic number 96. This transuranic actinide element was named after eminent scientists Marie and Pierre Curie, both known for their research on radioactivity. Curium was first intentionally made by the team of Glenn T. Seaborg, Ralph A. James, and Albert Ghiorso in 1944, using the cyclotron at Berkeley. They bombarded the newly discovered element plutonium with alpha particles. This was then sent to the Metallurgical Laboratory at University of Chicago where a tiny sample of curium was eventually separated and identified. The discovery was kept secret until after the end of World War II. The news was released to the public in November 1947. Most curium is produced by bombarding uranium or plutonium with neutrons in nuclear reactors – one tonne of spent nuclear fuel contains ~20 grams of curium.

<span class="mw-page-title-main">Metallocene</span>

A metallocene is a compound typically consisting of two cyclopentadienyl anions (C
5
H
5
, abbreviated Cp) bound to a metal center (M) in the oxidation state II, with the resulting general formula (C5H5)2M. Closely related to the metallocenes are the metallocene derivatives, e.g. titanocene dichloride or vanadocene dichloride. Certain metallocenes and their derivatives exhibit catalytic properties, although metallocenes are rarely used industrially. Cationic group 4 metallocene derivatives related to [Cp2ZrCH3]+ catalyze olefin polymerization.

<span class="mw-page-title-main">Titanium tetrachloride</span> Inorganic chemical compound

Titanium tetrachloride is the inorganic compound with the formula TiCl4. It is an important intermediate in the production of titanium metal and the pigment titanium dioxide. TiCl4 is a volatile liquid. Upon contact with humid air, it forms thick clouds of titanium dioxide and hydrochloric acid, a reaction that was formerly exploited for use in smoke machines. It is sometimes referred to as "tickle" or "tickle 4", as a phonetic representation of the symbols of its molecular formula.

Uranocene, U(C8H8)2, is an organouranium compound composed of a uranium atom sandwiched between two cyclooctatetraenide rings. It was one of the first organoactinide 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 known practical applications.

<span class="mw-page-title-main">Organoactinide chemistry</span> Study of chemical compounds containing actinide-carbon bonds

Organoactinide chemistry is the science exploring the properties, structure, and reactivity of organoactinide compounds, which are organometallic compounds containing a carbon to actinide chemical bond.

<span class="mw-page-title-main">Organouranium chemistry</span> Area of chemistry

Organouranium chemistry is the science exploring the properties, structure, and reactivity of organouranium compounds, which are organometallic compounds containing a carbon to uranium chemical bond. The field is of some importance to the nuclear industry and of theoretical interest in organometallic chemistry.

<span class="mw-page-title-main">Ken Raymond</span> American inorganic chemist

Kenneth Norman Raymond is a bioinorganic and coordination chemist. He is Chancellor's Professor of Chemistry at the University of California, Berkeley, Professor of the Graduate School, the Director of the Seaborg Center in the Chemical Sciences Division at Lawrence Berkeley National Laboratory, and the President and Chairman of Lumiphore.

<span class="mw-page-title-main">Dipotassium cyclooctatetraenide</span> Chemical compound

Dipotassium cyclooctatetraenide, sometimes abbreviated K2COT, is an organopotassium compound with the formula K2C8H8. It is a brown solid that is used as a precursor to cyclooctatetraenide complexes, such as uranocene (U(C8H8)2). Analogs of K2C8H8 are known with ring substituents, with different alkali metals, and with various complexants.

<span class="mw-page-title-main">Actinide chemistry</span> Branch of nuclear chemistry

Actinide chemistry is one of the main branches of nuclear chemistry that investigates the processes and molecular systems of the actinides. The actinides derive their name from the group 3 element actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide. All but one of the actinides are f-block elements, corresponding to the filling of the 5f electron shell; lawrencium, a d-block element, is also generally considered an actinide. In comparison with the lanthanides, also mostly f-block elements, the actinides show much more variable valence. The actinide series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.

<span class="mw-page-title-main">Actinocene</span> Class of chemical compounds

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.

In organometallic chemistry, f-block metallocenes are a class of sandwich compounds consisting of an f-block metal and a set of electron-rich ligands such as the cyclopentadienyl anion.

<span class="mw-page-title-main">Thorium compounds</span> Chemical compounds

Many compounds of thorium are known: this is because thorium and uranium are the most stable and accessible actinides and are the only actinides that can be studied safely and legally in bulk in a normal laboratory. As such, they have the best-known chemistry of the actinides, along with that of plutonium, as the self-heating and radiation from them is not enough to cause radiolysis of chemical bonds as it is for the other actinides. While the later actinides from americium onwards are predominantly trivalent and behave more similarly to the corresponding lanthanides, as one would expect from periodic trends, the early actinides up to plutonium have relativistically destabilised and hence delocalised 5f and 6d electrons that participate in chemistry in a similar way to the early transition metals of group 3 through 8: thus, all their valence electrons can participate in chemical reactions, although this is not common for neptunium and plutonium.

<span class="mw-page-title-main">Neptunocene</span> Chemical compound

Neptunocene, Np(C8H8)2, is an organoneptunium compound composed of a neptunium atom sandwiched between two cyclooctatetraenide (COT2-) rings. As a solid it has a dark brown/red colour but it appears yellow when dissolved in chlorocarbons, in which it is sparingly soluble. The compound is quite air-sensitive.

Cerium compounds are compounds containing the element cerium (Ce), a lanthanide. Cerium exists in two main oxidation states, Ce(III) and Ce(IV). This pair of adjacent oxidation states dominates several aspects of the chemistry of this element. Cerium(IV) aqueous solutions may be prepared by reacting cerium(III) solutions with the strong oxidizing agents peroxodisulfate or bismuthate. The value of E(Ce4+/Ce3+) varies widely depending on conditions due to the relative ease of complexation and hydrolysis with various anions, although +1.72 V is representative. Cerium is the only lanthanide which has important aqueous and coordination chemistry in the +4 oxidation state.

Protactinium compounds are compounds containing the element protactinium. These compounds usually have protactinium in the +5 oxidation state, although these compounds can also exist in the +2, +3 and +4 oxidation states.

Neptunium compounds are compounds containg the element neptunium (Np). Neptunium has five ionic oxidation states ranging from +3 to +7 when forming chemical compounds, which can be simultaneously observed in solutions. It is the heaviest actinide that can lose all its valence electrons in a stable compound. The most stable state in solution is +5, but the valence +4 is preferred in solid neptunium compounds. Neptunium metal is very reactive. Ions of neptunium are prone to hydrolysis and formation of coordination compounds.

<span class="mw-page-title-main">Plutonium compounds</span> Chemical compounds containing the element plutonium

Plutonium compounds are compounds containing the element plutonium (Pu). At room temperature, pure plutonium is silvery in color but gains a tarnish when oxidized. The element displays four common ionic oxidation states in aqueous solution and one rare one:

Americium compounds are compounds containing the element americium (Am). These compounds can form in the +2, +3, and +4, although the +3 oxidation state is the most common. The +5, +6 and +7 oxidation states have also been reported.

<span class="mw-page-title-main">Organothorium chemistry</span> Study of the carbon-thorium bond

Organothorium chemistry describes the synthesis and properties of organothorium compounds, chemical compounds containing a carbon to thorium chemical bond.

References

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.