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Thorium(IV) chloride

Thorium(IV) chloride describes a family of inorganic compounds with the formula ThCl<sub>4</sub>(H<sub>2</sub>O)<sub>n</sub>. Both the anhydrous and tetrahydrate (n = 4) forms are known. They are hygroscopic, water-soluble white salts.

Structures

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

Synthesis

ThCl<sub>4</sub> was an intermediate in the original isolation of thorium metal by Jons Jacob Berzelius.

Thorium(IV) chloride can be produced in a variety of ways. One method is a carbothermic reaction, 700&nbsp;°C to 2600&nbsp;°C, involving thorium oxides and carbon in a stream of chlorine gas:

ThO<sub>2</sub> + 2C + 4Cl<sub>2</sub> → ThCl<sub>4</sub> + 2CO

The chlorination reaction can be effected with carbon tetrachloride:

Th(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub> + CCl<sub>4</sub> → ThCl<sub>4</sub> + 3CO + 3CO<sub>2</sub>

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

Th + 6NH<sub>4</sub>Cl → (NH<sub>4</sub>)<sub>2</sub>ThCl<sub>6</sub> + 4NH<sub>3</sub> + 2H<sub>2</sub>

The hexachloride salt is then heated at 350&nbsp;°C under a high vacuum to produce ThCl<sub>4</sub>.

Reactions

Lewis base adducts

ThCl<sub>4</sub> reacts with Lewis bases to give molecular adducts, such as ThCl<sub>4</sub>(DME)<sub>2</sub> and ThCl<sub>4</sub>(TMEDA)<sub>2</sub>.

Reduction to Th metal

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

  1. Reduction of ThCl<sub>4</sub> with alkali metals.
  2. Electrolysis of anhydrous thorium(IV) chloride in fused mixture of NaCl and KCl.
  3. Ca reduction of a mixture of ThCl<sub>4</sub> with anhydrous zinc chloride.

References