Thorium(IV) chloride

Thorium(IV) chloride (ThCl₄) is an inorganic chemical compound. In addition to the anhydrous ThCl₄, two hydrates have been reported: ThCl₄(H₂O)₄[1] and ThCl₄(H₂O)₈.[2] These hygroscopic salts are water-soluble and white, at room temperature. Similar to other thorium complexes thorium(IV) chloride has a high melting point 770 °C (1,418 °F) and a boiling point of 921 °C (1,690 °F). Like all the other actinides, thorium is radioactive and has sometimes been used in the production of nuclear energy. Thorium(IV) chloride does not appear naturally.

Thorium(IV) chloride

Identifiers
CAS Number	10026-08-1
3D model (JSmol)	Interactive image
ECHA InfoCard	100.030.039
PubChem CID	66209
UNII	24Q3L637MM
CompTox Dashboard (EPA)	DTXSID6064905
InChI InChI=1S/4ClH.Th/h4*1H;/q;;;;+4/p-4
SMILES Cl[Th](Cl)(Cl)Cl
Properties
Chemical formula	ThCl4
Molar mass	373.849 g/mol
Appearance	white needles hygroscopic
Density	4.59 g/cm^3, solid
Melting point	770 °C (1,420 °F; 1,040 K)
Boiling point	921 °C (1,690 °F; 1,194 K)
Structure
Crystal structure	tetragonal
Hazards
EU classification (DSD) (outdated)	not listed
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Structures

Alternative view of the structure of solid ThCl₄.

The structure of thorium(IV) chloride features 8-coordinate Th centers with doubly bridging chloride ligands.[3]

Synthesis

ThCl₄ was an intermediate in the original isolation of thorium metal by Jons Jacob Berzelius.[4]

Thorium(IV) Chloride can be produced in a variety of ways, but the most common starting reactant is either thorium dioxide or Thorium (IV) orthosilicate.

One method, a carbothermic reaction, 700 °C to 2600 °C, involving thorium oxides and carbon in a stream of chlorine gas:

ThO₂ + 2 C + 4 Cl₂ → ThCl₄ + 2 CO

The chlorination reaction can be effected with carbon tetrachloride:[5][6]

Th(C₂O₄)₂ + CCl₄ → ThCl₄ + 3 CO + 3 CO₂

In another two-step method, thorium metal reacts with ammonium chloride:

Th + 6 NH₄Cl → (NH₄)₂ThCl₆ + 4 NH₃ + 2 H₂

The hexachloride salt is then heated at 350 °C under a high vacuum to produce ThCl₄.[7]

Reactions

ThCl₄ reacts with Lewis bases to give molecular adducts, such as ThCl₄(DME)₂ and ThCl₄(TMEDA)₂.[7]

Conversion to Th metal

Thorium(IV) chloride is an intermediate in the purification of thorium, which can be effected by

1. Reduction of ThCl₄ with alkali metals.
2. Electrolysis of anhydrous thorium(IV) chloride in fused mixture of NaCl and KCl.
3. Ca reduction of a mixture of ThCl₄ with anhydrous zinc chloride.[8]

References

1. Cantat, Thibault; Scott, Brian L.; Kiplinger, Jaqueline L. "Convenient Access to the Anhydrous Thorium Tetrachloride Complexes ThCl₄(DME)₂, ThCl₄(1,4-dioxane)₂ and ThCl₄(THF)_3.5 using Commercially Available and Inexpensive Starting Materials" Chemical Communications 2010, 46, 919-921. doi:10.1039/b923558b
2. P. Ehrlich "Titanium, Zirconium, Hafnium, and Thorium" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1203.
3. Mason, J. T.; Jha, M. C.; Chiotti, P. (1974). "Crystal Structures of ThCl₄ Polymorphs". Journal of the Less Common Metals. 34: 143–151. doi:10.1016/0022-5088(74)90224-0.
4. Weeks, Mary Elvira (1932-07-01). "The Discovery of the Elements. XI. Some Elements Isolated with the Aid of Potassium and Sodium: Zirconium, Titanium, Cerium, and Thorium". Journal of Chemical Education. 9 (7): 1231. Bibcode:1932JChEd...9.1231W. doi:10.1021/ed009p1231. ISSN 0021-9584.
5. Brauer, Georg (1963). Handbook Of Preparative Inorganic Chemistry. New York: Academic Press.
6. Gutierrez, R. L.; Herbst, R. J. (October 1979). "Preliminary Fabrication Studies of Alternative LMFBR Carbide Fuels". Los Alamos Scientific Laboratory.
7. Cantat, Thibault; Scott, Brian L.; Kiplinger, Jaqueline L. (2010-01-25). "Convenient Access to the Anhydrous Thorium Tetrachloride Complexes ThCl₄(DME)₂, ThCl₄(1,4-dioxane)₂ and ThCl₄(THF)_3.5 using Commercially Available and Inexpensive Starting Materials". Chemical Communications. 46 (6): 919–21. doi:10.1039/b923558b. ISSN 1364-548X. PMID 20107650.
8. "Periodic Table of Elements: Los Alamos National Laboratory". periodic.lanl.gov. Retrieved 2016-04-29.