 | |
| Names | |
|---|---|
| IUPAC name Plutonium(III) chloride | |
| Other names Plutonium trichloride | |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider |
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| Properties | |
| Cl3Pu | |
| Molar mass | 350.322 g/mol |
| Appearance | Green solid |
| Density | 5.71 g/cm3, solid[1] |
| Melting point | 767 °C (1,413 °F; 1,040 K)[1] |
| Boiling point | 1,767 °C (3,213 °F; 2,040 K)[1] |
| Related compounds | |
Otheranions | Plutonium(III) fluoride Plutonium(III) bromide Plutonium(III) iodide |
Othercations | Samarium(III) chloride |
Related plutonium chlorides | Plutonium(IV) chloride |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Plutonium(III) chloride orplutonium trichloride is a chemical compound with the formulaPuCl3.[1] It is the only stable solidchloride ofplutonium, though another plutonium chloride,plutonium tetrachloride, is known in the gas phase.[2]: 1092 It can either be found as ananhydrous solid (containing no water), or in the form ofhydrates (solids containing water), such as the hexahydrate,PuCl3·6H2O.[2]: 1100 It is used in the processing of plutonium metal[2]: 864, 870 and inmolten-salt reactors.[3][4]
Multiple different methods have been used to synthesize plutonium(III) chloride, which all involve thechlorination of plutonium orplutonium compounds. Many of these methods useplutonium(III) oxalate, which can be prepared by carefully addingoxalic acid to anacidic plutonium(III)solution, resulting in thedecahydrate,Pu2(C2O4)3·10H2O.[2]: 1092–1093
After it is synthesized, it is advised that it be purified bysublimation in a sealed quartz tube.[2]: 1092–1093
For medium-scale reactions (between 1 and 10 grams), the best method of preparing plutonium(III) chloride is by reacting plutonium(III) oxalate withhydrogen chloride, HCl. The reaction proceeds like so:[2]: 1093
For processing 100 gram quantities of plutonium,plutonium hydride can be reacted with hydrogen chloride in afluidized bed reactor at 450 °C. To removeoxychlorides, the resultingPuCl3 is melted at 800 °C andsparged with HCl.[2]: 1093
Plutonium(III) chloride can also be formed fromaqueous solutions of hydrogen chloride (hydrochloric acid). Upon evaporation of the HCl solution, a residue of plutonium(III) chloridehexahydrate,PuCl3·6H2O, is formed. The hexahydrate can then bedehydrated in a stream of HCl to give theanhydrous solid.[2]: 1093
Due to the difficulty in handling hazardous gases,hexachloropropene (C3Cl6) can be used as achlorinating agent instead of more dangerous compounds. Plutonium(III) oxalate (Pu2(C2O4)3) has been reported to be an efficient initial source of plutonium. To produce plutonium(III) chloride,Pu2(C2O4)3 is heated withC3Cl6:[3]
Plutonium(III) chloride can be produced via reacting plutonium metal with chlorine gas at temperatures between 300 °C and 500 °C, followed bysublimation at 600–800 °C.[2]: 1093 Chlorine can also be used to chlorinateplutonium(IV) oxide (PuO2). ForPuO2 chlorination,carbon is used as areducing agent. The reaction proceeds as follows:[4]
Plutonium(IV) oxide can also be chlorinated withphosgene (COCl2) orcarbon tetrachloride, yielding analytically pure samples ofPuCl3. This method has been used atLos Alamos National Laboratory. One method for the continuous production ofPuCl3 using phosgene is as follows:[2]: 1093
Plutonium(IV) oxalate hydrate (Pu(C2O4)2·6H2O) is precipitated from plutonium(IV) solution, dried, andcalcined (heated todecomposition without oxygen) to form plutonium(IV) oxide (PuO2). The resultingPuO2 is then heated with phosgene in atube furnace at 500 °C. This method produces plutonium at a rate of 250 grams / hour.[2]: 1093
To ensure a high-purity product, plutonium(III) chloride can be prepared by reacting plutonium metal withammonium chloride at high temperature. The ammonium chloridesublimes, producingammonia and hydrogen chloride. The hydrogen chloride subsequently reacts with the plutonium metal to formPuCl3. The overall reaction follows like so:[5]
Plutonium(III) chloride is formed unintentionally from the corrosion of plutonium metal byhydrogen chloride gas:[6]
The color of plutonium(III) chloride depends on its method of production. Plutonium(III) chloride produced via dehydration of the hexahydrate is slate-blue, while when prepared by one of theanhydrous methods the compound is blue-green to emerald green. Whencondensated from the gas phase, it appears as an emerald green solid.[2]: 1093 It is incrediblyhygroscopic, and is readily hydrated by atmospheric moisture.[4] This leads to the formation of severalhydrates, or compounds containing water. These include the monohydrate (PuCl3·H2O), dihydrate (PuCl3·2H2O), and hexahydrate (PuCl3·6H2O). Which hydrate is formed depends on thepartial pressure of water in the atmosphere.[2]: 1100 Plutonium(III) chloride hexahydrate has a melting point of 94 °C, at which it melts in its ownwaters of crystallization, forming a solution. In a vacuum at 27 °C, it decomposes to give the monohydrate, and upon heating between 400 and 520 °C, it givesplutonium oxychloride, PuOCl.[7]: 130, 140
When heated with chlorine at high temperatures, plutonium(III) chloride reacts to form the compoundplutonium tetrachloride, increasing itsvolatility. Upon condensing, it reverts toPuCl3.[2]: 1094
The compound isantiferromagnetic below around 4.5 K.[8]
AnhydrousPuCl3 isisostructural with (has the same structure as) the relateduranium(III) chloride,UCl3, having ahexagonal structure. Each plutonium atom is surrounded by nine chlorine atoms. Six of the nine chlorine atoms form atriangular prism, which have Pu-Cl bond lengths of 2.886 Å. Each of three rectangular sides of the triangular prism are capped off by chlorine atoms, which have Pu-Cl distances of 2.919 Å. This gives each plutonium atom acoordination geometry oftricapped trigonal prismatic. The prisms' triangular bases connect to form infinite chains. This structure is related to the structures ofplutonium(III) bromide (PuBr3) andplutonium(III) iodide (PuI3); however, one of the threebromine oriodine atoms that would have capped off one of the rectangular sides of the triangular prism is too far away from the plutonium atom to bond.[2]: 1096–1097 Unlike inPuBr3, where the Pu-Br bonds are predominantlycovalent, the Pu-Cl bonds withinPuCl3 are predominantlyionic.[2]: 1100
Plutonium(III) chloridehexahydrate,PuCl3·6H2O, adopts theGdCl3·6H2O-type structure,[note 1] which is seen across all thelanthanide chlorides except those oflanthanum andcerium. In this structure, each plutonium atom is bonded to six waterligands and twochloride ligands, formingmonomericPuCl2(H2O)+6 groups. ThePuCl2(H2O)+6 groups are linked together by chloride ions viahydrogen bonding.[10]
Plutonium(III) chloride trihydrate (PuCl3·3H2O) adopts the same structure asthe corresponding neodymium compound,NdCl3·3H2O.[4]
Plutonium(III) chloride is an important intermediate in the production of plutonium metal. Plutonium metal produced from thereduction ofplutonium tetrafluoride andplutonium(IV) oxide can be impure, notably withamericium created via thebeta decay ofplutonium-241. To separate americium impurities from plutonium, the impure plutonium metal is placed in a mixture of moltenmagnesium chloride,sodium chloride, andpotassium chloride. Plutonium(III) chloride is produced when plutonium metal isoxidized by the magnesium chloride, but is subsequently reduced back to plutonium metal by americium. The reactions that occur are:[2]: 869–870
After the americium is oxidized, theamericium(III) chloride andmolten salt mixture can be separated, leaving a plutonium metal button behind.[2]: 870
Plutonium(III) chloride is a common nuclear material for use inmolten-salt reactors, reactors which usemolten salts in whichactinides aredissolved as their fuel, such as a mixture ofsodium chloride and plutonium(III) chloride. Molten salts containingchlorides, like plutonium(III) chloride, are often used, as they have low melting points and can dissolve high concentrations of actinides.[3][4][5]
As with allplutonium compounds, it is subject to control under theNuclear Non-Proliferation Treaty. Due to the radioactivity of plutonium, all of its compounds, PuCl3 included, are warm to the touch. Such contact is not recommended, since touching the material may result in serious injury.[citation needed] Due to plutonium(III) chloride's highhygroscopicity, it must be kept in an controlled, dehumidified atmosphere.[4]
