Plutonium tetrachloride

Plutonium tetrachloride or plutonium(IV) chloride is an inorganic compound of plutonium and chlorine with the chemical formula PuCl₄. While it is not known as a solid, gaseous PuCl₄ is known. In addition, it is known to form several stable adducts. The dimethoxyethane adduct, PuCl₄(DME)₂, has been used as a precursor to other plutonium compounds.

Plutonium tetrachloride

Names
IUPAC name Plutonium(IV) chloride
Identifiers
CAS Number	161280-01-9 N
3D model (JSmol)	Interactive image
CompTox Dashboard (EPA)	DTXSID90615460
InChI InChI=1S/4ClH.Pu/h4*1H;/q;;;;+4/p-4 Key: QNJPYBOCFFOTGM-UHFFFAOYSA-J
SMILES [Cl-].[Cl-].[Cl-].[Cl-].[Pu+4]
Properties
Chemical formula	PuCl4
Molar mass	386 g·mol−1
Related compounds
Other anions	Plutonium tetrafluoride
Other cations	Neptunium tetrachloride Uranium tetrachloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Synthesis

The compound is formed when plutonium trichloride is put in a stream of chlorine:^[1]: 1094

2 PuCl₃ + Cl₂ → 2 PuCl₄

Physical properties

The compound is not stable as a solid; however, it is known in the gas phase. When condensed, it forms plutonium(III) chloride and chlorine gas:^[1]: 1094

2 PuCl₄ → 2 PuCl₃ + Cl₂

However, several stable adducts, such as with dimethoxyethane (PuCl₄(DME)₂)^[2] or diphenylsulfoxide,^[3] and ammoniates (solids incorporating ammonia),^[4] are known. The diphenylsulfoxide adduct appears as a red solid.^[3]

Complexes

With dimethoxyethane

Plutonium tetrachloride forms a stable adduct with dimethoxyethane (CH₃OCH₂CH₂OCH₃) with formula PuCl₄(DME)₂ (DME=dimethoxyethane). This compound can be prepared via evaporation of a hydrochloric acid solution containing plutonium(IV), adding the product to dimethoxyethane, and then adding trimethylsilyl chloride.^[2] This adduct can be used to prepare other compounds. For example, when it is dissolved in tetrahydrofuran, it is partially reduced to form the mixed-valence complex [Pu^IIICl₂(THF)₅]⁺[Pu^IVCl₅(THF)]⁻. (THF=tetrahydrofuran).^[5] It has also been used to prepare the compound plutonium(IV) N-(tert-butyl)isobutyramide (Pu(ita)₄, ita=N-(tert-butyl)isobutyramide) through reaction with potassium N-(tert-butyl)isobutyramide. Pu(ita)₄ has been investigated in the production of oxidation state-pure plutonium(IV) oxide.^[6]

The structure of the dimethoxyethane adduct of plutonium tetrachloride. Green represents chlorine atoms, red represents oxygen atoms, grey represents carbon atoms, white represents hydrogen atoms, and blue represents plutonium atoms.

Other complexes

Plutonium tetrachloride also forms an adduct with diphenylsulfoxide (Ph₂SO). This adduct has been prepared by boiling a solution consisting of plutonium(IV) dissolved in hydrochloric acid, suspending the residue in acetonitrile, and adding to it an acetonitrile solution of diphenylsulfoxide. The resulting product has the formula PuCl₄(Ph₂SO)₃, and is a rare example of plutonium in its +4 oxidation state with a coordination number of 7 (forming 7 bonds).^[3]

When the related compound dicaesium hexachloroplutonate is reacted with liquid ammonia at low temperatures, the ammoniate (solid incorporating ammonia). The initial product has composition PuCl₄·~7–8NH₃, which decomposes over a period of weeks to form PuCl₄·5NH₃. PuCl₄·5NH₃ is stable at room temperature. Both compounds are ammine complexes, meaning that the ammonia in them is bonded to the plutonium atoms.^[4]

Uses

A mixture of uranium tetrachloride and plutonium tetrachloride can be used as fuel for nuclear reactors.^[7]

Related compounds

Anionic derivatives

Main articles: Hexachloroplutonate and Dicaesium hexachloroplutonate

Even though binary plutonium(IV) chloride is not known as a solid, solid compounds derived from it, such as dicaesium hexachloroplutonate (Cs₂PuCl₆), are known.^[1]: 1094 In this compound, the +4 oxidation state of plutonium is stabilized by complexing with caesium chloride.^[8]: 149 It is made up of discrete hexachloroplutonate (PuCl2−6) ions.^[1]

Diagram of the hexachloroplutonate ion. Green spheres represent chlorine atoms, and blue spheres represent plutonium atoms.