Thorium compounds
![](http://upload.wikimedia.org/wikipedia/commons/thumb/6/6e/Thorium_reactions.svg/350px-Thorium_reactions.svg.png)
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.[1] 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 (thus including thorium and uranium) 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.[2]
General chemistry
A thorium atom has 90 electrons, of which four are
The ground-state electron configurations of thorium ions are as follows: Th+, [Rn]6d27s1; Th2+, [Rn]5f16d1;
Thorium is a highly
Finely divided thorium metal presents a fire hazard due to its
The most important
In aqueous solution, thorium occurs exclusively as the tetrapositive
Large coordination numbers are the rule: thorium nitrate pentahydrate was the first known example of coordination number 11, the oxalate tetrahydrate has coordination number 10, and the Th(NO
3)−
6 anion in the calcium and magnesium salts is 12-coordinate.[2] Due to the large size of the Th4+ cation, thorium salts have a weaker tendency to hydrolyse than that of many multiply charged ions such as Fe3+, but hydrolysis happens more readily at pH above 4, forming various polymers of unknown nature, culminating in the formation of the gelatinous hydroxide:[16] this behaviour is similar to that of protactinium, which also hydrolyses readily in water to form colloidal precipitates.[1] The distinctive ability of thorium salts is their high solubility, not only in water, but also in polar organic solvents.[15] As a hard Lewis acid, Th4+ favours hard ligands with oxygen atoms as donors: complexes with sulfur atoms as donors are less stable.[2]
The
Th4+ + e− ⇌ Th3+ E0 = −3.8 V Th4+ + 4e− ⇌ Th E0 = −1.83 V
Oxides and hydroxides
![](http://upload.wikimedia.org/wikipedia/commons/thumb/3/3f/CaF2_polyhedra.png/250px-CaF2_polyhedra.png)
In air, thorium burns to form the
Reports of thorium peroxide, initially supposed to be Th2O7 and be formed from reacting thorium salts with hydrogen peroxide, were later discovered to contain both peroxide anions and the anions of the reacting thorium salt.[13]
Thorium monoxide has been produced through laser ablation of thorium in the presence of oxygen.[23] This highly polar molecule is calculated to have one of the largest known internal electric fields.[24]
3)
2•½H
2O or Th(OH)
2CO
3•2H
2O.[13][25] Several mixed oxides are known, such as BaThO3, which has the perovskite structure.[22]
Halides
![](http://upload.wikimedia.org/wikipedia/commons/thumb/8/8d/Kristallstruktur_Uran%28IV%29-fluorid.png/220px-Kristallstruktur_Uran%28IV%29-fluorid.png)
All four thorium tetrahalides are known, as are some low-valent bromides and iodides:[14] the tetrahalides are all hygroscopic compounds that dissolve easily in polar solvents such as water.[26] Additionally, many related polyhalide ions are also known.[14] Thorium tetrafluoride (ThF4, white, m.p. 1068 °C) is most easily produced by reacting various thorium salts, thoria, or thorium hydroxide with hydrogen fluoride: methods that involve steps in the aqueous phase are more difficult because they result in hydroxide and oxide fluorides that have to be reduced with hydrogen fluoride or fluorine gas.[14] It has a monoclinic crystal structure and is isotypic with zirconium tetrafluoride and hafnium tetrafluoride, where the Th4+ ions are coordinated with F− ions in somewhat distorted square antiprisms.[14] It is a white, hygroscopic powder: at temperatures above 500 °C, it reacts with atmospheric moisture to produce the oxyfluoride ThOF2.[27]
Thorium tetrabromide (ThBr4, white, m.p. 679 °C) can be produced either by reacting thorium(IV) hydroxide with
Many polynary halides with the alkali metals, barium, thallium, and ammonium are known for thorium fluorides, chlorides, and bromides.[14] For example, when treated with potassium fluoride and hydrofluoric acid, Th4+ forms the complex anion ThF2−
6, which precipitates as an insoluble salt, K2ThF6.[10]
Chalcogenides and pnictides
The heavier chalcogens sulfur, selenium, and tellurium are known to form thorium chalcogenides, many of which have more complex structure than the oxides. Apart from several binary compounds, the oxychalcogenides ThOS (yellow), ThOSe, and ThOTe are also known.[29] The five binary thorium sulfides – ThS (lustrous metallic), Th2S3 (brown metallic), Th7S12 (black), ThS2 (purple-brown), and Th2S5 (orange-brown) – may be produced by reacting hydrogen sulfide with thorium, its halides, or thoria (the last if carbon is present): they all hydrolyse in acidic solutions.[29] The six selenides are analogous to the sulfides, with the addition of ThSe3.[29] The five tellurides are also similar to the sulfides and selenides (although Th2Te5 is unknown), but have slightly different crystal structures: for example, ThS has the sodium chloride structure, but ThTe has the caesium chloride structure, since the Th4+ and Te2− ions are similar in size while the S2− ions are much smaller.[29]
All five chemically characterised
Other inorganic compounds
Thorium reacts with hydrogen to form the thorium hydrides ThH2 and Th4H15, the latter of which is superconducting below the transition temperature of 7.5–8 K; at standard temperature and pressure, it conducts electricity like a metal.[12] Thorium is the only metallic element that readily forms a hydride higher than MH3.[31] Finely divided thorium metal reacts very readily with hydrogen at standard conditions, but large pieces may need to be heated to 300–400 °C for a reaction to take place.[12] Around 850 °C, the reaction forming first ThH2 and then Th4H15 occurs without breaking up the structure of the thorium metal.[12] Thorium hydrides react readily with oxygen or steam to form thoria, and at 250–350 °C quickly react with hydrogen halides, sulfides, phosphides, and nitrides to form the corresponding thorium binary compounds.[12]
Three binary thorium
Coordination compounds
Many other inorganic thorium compounds with polyatomic anions are known, such as the
4)
4•4H
2O, while thorium nitrate forms tetra- and pentahydrates, is soluble in water and alcohols, and is an important intermediate in the purification of thorium and its compounds.[25]
Thorium halides can often coordinate with lewis-acid solvents such as tetrahydrofuran and pyridine as follows:
- ThX4 + THF → ThX4(THF)3
Due to its great tendency towards hydrolysis, thorium does not form simple carbonates, but rather carbonato complexes such as [Th(CO
3)
5]6−
, similarly to uranium(IV) and plutonium(IV).[18] Thorium forms a stable tetranitrate, Th(NO
3)
4•5H
2O, a property shared only by plutonium(IV) among the actinides: it is the most common thorium salt and was the first known example of an 11-coordinated compound. Another example of the high coordination characteristic of thorium is [Th(C
5H
5NO)
6(NO
3)
2]2+
, a 10-coordinated complex with distorted bicapped antiprismatic molecular geometry.[18] The anionic [Th(NO
3)
6]2−
is isotypic to its cerium, uranium, neptunium, and plutonium analogues and has a distorted icosahedral structure.[18] Particularly important is the borohydride, Th(BH
4)
4, first prepared in the Manhattan Project along with its uranium(IV) analogue. It is produced as follows:[18]
- ThF4 + 2 Al(BH4)3 → Th(BH
4)
4 + 2 AlF2BH4
following which thorium borohydride can be easily isolated, as it sublimes out of the reaction mixture. Like its protactinium(IV) and uranium(IV) analogues, it is a thermally and chemically stable compound where thorium has a coordination number of 14 with a bicapped hexagonal antiprismatic molecular geometry.[18]
Organometallic compounds
![](http://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Uranocene-3D-balls.png/120px-Uranocene-3D-balls.png)
Most of the work on organothorium compounds has focused on the
The simplest of the cyclopentadienyls are ThIII(C
5H
5)
3 and ThIV(C
5H
5)
4: many derivatives are known. The first (which has two forms, one purple and one green) is a rare example of thorium in the formal +3 oxidation state.[35][34] In the derivative [ThIII{η5-C5H3(SiMe3)2}3], a blue paramagnetic compound, the molecular geometry is trigonal planar around the thorium atom, which has a [Rn]6d1 configuration instead of the expected [Rn]5f1. [ThIII{η5-C5H3(SiMe3)2}3] can be reduced to the anion [ThII{η5-C5H3(SiMe3)2}3]−, in which thorium exhibits a very rare +2 oxidation state.[36] The second is prepared by heating thorium tetrachloride with K(C
5H
5) under reflux in benzene: the four cyclopentadienyl rings are arranged tetrahedrally around the central thorium atom. The halide derivative Th(C
5H
5)
3Cl can be made similarly by reducing the amount of K(C
5H
5) used (other univalent metal cyclopentadienyls can also be used), and the chlorine atom may be further replaced by other halogens or by alkoxy, alkyl, aryl, or BH4 groups. Of these, the alkyl and aryl derivatives have been investigated more deeply due to the insight they give regarding the nature of the Th–C σ bond.[35] Of special interest is the dimer [Th(η5-C5H5)2-μ-(η5,η1-C5H5)]2, where the two thorium atoms are bridged by two cyclopentadienyl rings, similarly to the structure of niobocene.[35]
Tetrabenzylthorium, Th(CH
2C
6H
5), is known, but its structure has not yet been determined. Thorium forms the monocapped trigonal prismatic anion [Th(CH3)7]3−, heptamethylthorate, which forms the salt [Li(tmeda)]3[ThMe7] (tmeda = Me2NCH2CH2NMe2). Although one methyl group is only attached to the thorium atom (Th–C distance 257.1 pm) and the other six connect the lithium and thorium atoms (Th–C distances 265.5–276.5 pm) they behave equivalently in solution. Tetramethylthorium, Th(CH
3)
4, is not known, but its
See also
Notes
- ^ [Rn]6d2 is a very low-lying excited state configuration of Th2+.[3]
- ^ Among the low number of other known thorium oxometallates are the arsenate, tungstate, germanate, silicate, borate, and perrhenate. While thorium titanates and tantalates are known, they are structurally more like double oxides than true oxometallates.[25]
References
- ^ a b Greenwood and Earnshaw, p. 1265
- ^ a b c d e f Cotton, Simon (2006). Lanthanide and Actinide Chemistry. John Wiley & Sons Ltd.
- ^ a b c d Wickleder et al., pp. 59–60
- ^ a b Greenwood and Earnshaw, p. 1266
- ^ Golub et al., pp. 222–7
- doi:10.1063/1.3253147. Archived from the original(PDF) on 11 February 2014. Retrieved 19 October 2013.
- ^ David R. Lide (ed), CRC Handbook of Chemistry and Physics, 84th Edition. CRC Press. Boca Raton, Florida, 2003; Section 10, Atomic, Molecular, and Optical Physics; Ionization Potentials of Atoms and Atomic Ions
- ^ a b c d e f g h Wickleder et al., pp. 61–63
- ISBN 0-8493-0485-7.
- ^ a b Hyde, Earl K. (1960). The radiochemistry of thorium (PDF). Subcommittee on Radiochemistry, National Academy of Sciences—National Research Council.
- ^ a b c Greenwood and Earnshaw, p. 1264
- ^ a b c d e Wickleder et al., pp. 64–6
- ^ a b c d e f g h Wickleder et al., pp. 70–7
- ^ a b c d e f g h i j k l m n o p q r s t u Wickleder et al., pp. 78–94
- ^ ISBN 978-5-7695-2533-9.
- ^ a b c d e f Wickleder et al., pp. 117–134
- .
- ^ a b c d e f Greenwood and Earnshaw, p. 1275–7
- ^ Greenwood and Earnshaw, p. 1263
- .
- ISBN 0-19-850340-7.
- ^ a b Greenwood and Earnshaw, p. 1269
- PMID 17912418.
- ^ "The ACME EDM Experiment." electronedm.org
- ^ a b c d e f Wickleder et al., pp. 101–115
- ^ a b Greenwood and Earnshaw, p. 1271
- ISBN 0-8493-8671-3.
- ^ Greenwood and Earnshaw, p. 1272
- ^ a b c d Wickleder et al., pp. 95–97
- ^ a b c Wickleder et al., pp. 97–101
- ^ Synthetic Milestones in f Element Inorganic Chemistry by Lester R. Morss
- ^ a b Wickleder et al., pp. 66–70
- ^ Greenwood and Earnshaw, p. 1267
- ^ a b c d Wickleder et al., pp. 116–7
- ^ a b c d Greenwood and Earnshaw, pp. 1278–80
- PMID 29560172.
Bibliography
- Golub, A. M. (1971). Общая и неорганическая химия (General and Inorganic Chemistry). Vol. 2.
- ISBN 978-0-08-037941-8.
- Wickleder, Mathias S.; Fourest, Blandine; Dorhout, Peter K. (2006). "Thorium". In Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean (eds.). The Chemistry of the Actinide and Transactinide Elements (PDF). Vol. 3 (3rd ed.). Dordrecht, the Netherlands: Springer. pp. 52–160. doi:10.1007/1-4020-3598-5_3. Archived from the original(PDF) on 2016-03-07.