Hexachloroplutonate

The hexachloroplutonate ion, PuCl2−6, is an ion containing plutonium and chlorine. It forms several salts, which are called hexachloroplutonates.^{[1][2]: 1104}

Hexachloroplutonate

The hexachloroplutonate dianion
Identifiers
3D model (JSmol)	Interactive image
InChI InChI=1S/6ClH.Pu/h6*1H;/q;;;;;;+4/p-6 Key: QYJYVEJBCPQDNB-UHFFFAOYSA-H
SMILES Cl[Pu-2](Cl)(Cl)(Cl)(Cl)Cl
Properties
Chemical formula	PuCl2−6
Molar mass	457 g·mol−1
Related compounds
Other anions	Hexafluoroplutonate
Other cations	Hexachloroplatinate; Hexachloropalladate; Hexachlorogermanate(IV)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Structure and bonding

The PuCl2−6 ion features a slightly distorted octahedral molecular geometry, with three distinct Pu-Cl bonds. The Pu-Cl bond lengths vary between 2.574 and 2.598 Å, and the Cl-Pu-Cl bond angles range between 88.54° and 91.46°.^[3]

The Pu-Cl bonds in PuCl2−6 are primarily ionic; however, they feature small but important amounts of covalent bonding. The chloride ligands bond using their s and p electrons, while plutonium bonds using its s, d, and f electrons. The Pu-Cl bond order is less than 1, and the shape of the Pu-Cl bond slightly deviates from cylindrical, possibly indicating a small amount of pi bonding.^[3] The 5f electrons in the PuCl2−6 have a large nephelauxetic effect^[4] (decrease in electron-electron repulsion).

In aqueous solution

It is the dominant species of plutonium(IV) in 11 M hydrochloric acid solution.^[5]

Salts

The PuCl2−6 ion forms several salts. Dicaesium hexachloroplutonate (Cs₂PuCl₆) is a pale yellow solid which is precipitated from concentrated HCl solution by the addition of caesium chloride. Cs₂PuCl₆ can be used to prepare other plutonium compounds, such as the cyclopentadienide complex (η⁵-C₅H₅)₃PuCl, and it has been proposed for use in the purification of plutonium metal. It has been used as a reference for plutonium(IV), and due to its stability, it has been proposed for use as a primary standard for plutonium.^{[2]: 839, 1104, 1191 [5]} Potassium and rubidium hexachloroplutonates, K₂PuCl₆ and Rb₂PuCl₆, are also known. They are prepared by heating mixtures of plutonium(III) chloride and the respective alkali metal chlorides under high chlorine pressures.^[6]

PuCl2−6 is also known to form salts with quaternary ammonium cations, including tetramethylammonium, tetraethylammonium,^[2]: 1104 and tetrabutylammonium.^[7] The tetramethylammonium and tetraethylammonium salts, [NMe₄]₂[PuCl₆] and [NEt₄]₂[PuCl₆], form orange-yellow crystals.^[2]: 1109 [NEt₄]₂[PuCl₆] was used in the first synthesis of plutonocene.^[8] The tetrabutylammonium salt, [N(n-Bu)₄]₂[PuCl₆], is prepared by the addition of tetrabutylammonium chloride to plutonium(IV) in HCl aqueous solution. It is soluble in several organic solvents.^[7]

PuCl2−6 is also known to form salts with pyridinium, pyridinium dervatives,^[3][9] and tetraphenylphosphonium.^[10]