Thorium halides

The properties and structures of the halides are mainly exemplified in this chapter by a consideration of the halides of thorium and uranium. 

Apart from two rather ill-defined iodides in the +2 and +3 oxidation states, thorium forms exclusively halides in the +4 state. Heating thorium metal with ThLj affords Thl2 and ThI 3, the latter not well characterized. Thl2 exists in black and gold forms the high conductivity suggests that, like some of the apparent lanthanide(ii) iodides (Section 3.3.3), it contains free electrons and is in fact Th + (0 )2 (1 )2. 

All are white solids. Table 10.4 summarizes the structures of the thorium(iv) halides (the chloride and the bromide exist in two different forms in the solid state). 

Thorium halides form many complexes with neutral donors, discussed in chapter 11. Here it may be noted that there are a number of anionic complexes, including Cs2ThCl6, (pyH)2ThBr6, and (Bu4N)2ThIg, which generally seem to contain isolated [ThXs]  

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Thorium dioxide, 24 761-762 Thorium fluorides, 24 762 Thorium halides, 24 762-763 Thorium hydrides, 24 761 Thorium hydroxide, 24 756 Thorium iodides, 24 763 Thorium isotopes, 24 753-754... 

Thorium metal also can he prepared hy thermal reduction of its hahdes with calcium, magnesium, sodium, or potassium at elevated temperatures (950°C), first in an inert atmosphere and then in vacuum. Fluoride and chloride thorium salts are commonly employed. Berzehus first prepared thorium by heating tetrachloride, ThCh, with potassium. Magnesium and calcium are the most common reductant. These metals are added to thorium halides in excess to ensure complete reduction. Excess magnesium or calcium is removed by heating at elevated temperatures in vacuum. One such thermal reduction of hahdes produces thorium sponge, which can be converted into the massive metal by melting in an electron beam or arc furnace. 

The compound also can be prepared by many other methods including thermal decomposition of thorium oxalate, hydroxide, carbonate, or nitrate. Heating thorium metal in oxygen or air, and hydrolysis of thorium halides also yield thorium dioxide. 

Ammino-derivatives op Subgroup A—Derivatives of Titanium Kilts, Zirconium Salts, Cerium, and Thorium Halides. 

Allyl Complexes. Allyl complexes of thorium have been known since the 1960s and are usually stabilized by cyclopentadienyl ligands. Allyl complexes can be accessed via the interaction of a thorium halide and an allyl grignard. This synthetic method was utilized to obtain a rare example of a naked allyl complex, Th(r 3-C3H5)4 [144564-74-9], which decomposes at 0°C. This complex, when supported on dehydroxylated y-alumina, is an outstanding heterogeneous catalyst for arene hydrogenation and rivals the most active platinum metal catalysts in activity (17,18). 

Ketones, aldehydes, esters. Complexes of ketones, aldehydes, and esters have been made with uranium and thorium halide complexes by isolating the product from a ligand-containing solution. Ethyl- and -propyl acetates also react with uranium tetrachloride to yield mixed halide-acetate salts with ester as an additional coordinating base. 

The tetrahalides are the thorium halides of greatest practical importance. The tetrafluoride ThF4 is the preferred starting material for large-scale production of thorium metal (Sec. 10.4). ThF4 has been proposed as fertile material in the fuel mixture of the molten-salt reactor. The tetraiodide has been used as feed material in the iodide process for making very pure thorium metal (Sec. 10.4). 

This is a short progress report describing measurements of the vapour pressure of Thl4(cr) and Thl4(l). The work was presented in a Coirference paper [1980PRA/NAG] on the vaporisation of all the thorium halides, but no details are given it has not been published elsewhere. 

Table A-51 Vapour pressure of thorium halides, logio/>/bar = AIT + B.568...

With Acyl Halides, Hydrogen Halides, and Metallic Halides. Ethylene oxide reacts with acetyl chloride at slightly elevated temperatures in the presence of hydrogen chloride to give the acetate of ethylene chlorohydrin (70). Hydrogen haUdes react to form the corresponding halohydrins (71). Aqueous solutions of ethylene oxide and a metallic haUde can result in the precipitation of the metal hydroxide (72,73). The haUdes of aluminum, chromium, iron, thorium, and zinc in dilute solution react with ethylene oxide to form sols or gels of the metal oxide hydrates and ethylene halohydrin (74). 

The conductivities of thorium (III) and uranium (IV) halides in nitromethane are increased in the presence of a donor molecule from chloride to iodide and they also increase with increasing donicity of the neutral donor 49-53)... 

Thorium metal is generally prepared by the metallothermic reduction of its halides (Section II,A). Very high-quality metal containing a total of 250 ppm impurities has been prepared at the Ames Laboratory of the Department of Energy (98, 99). These workers reduced ThCl4 with excess Mg metal to yield a Th-Mg alloy, which was then heated in vacuo to remove the excess Mg (55) ... 

Thorium can be obtained from its halides by electrolysis. A fused salt bath of NaCl—KCl—ThCh or NaCl—KCl—KF—ThF4 or similar eutectic mixtures is employed in electrolysis. The electrolysis may be carried out in a graphite crucible, and thorium is deposited as a coarse powder on the electrode, which is made of molybdenum or other suitable material. 

Rubidium metal alloys with the other alkali metals, the alkaline-earth metals, antimony, bismuth, gold, and mercury. Rubidium forms double halide salts with antimony, bismuth, cadmium, cobalt, copper, iron, lead, manganese, mercury, nickel, thorium, and zinc. These complexes are generally water insoluble and not hygroscopic. The soluble rubidium compounds are acetate, bromide, carbonate, chloride, chromate, fluoride, formate, hydroxide, iodide,... 

Bromine reacts with some metal oxides, eg, thorium oxide, at high temperatures in the presence of reducing agents to form bromides (18). Certain nonhydrated metal halides can be formed by precipitation. These include AgBr, CuBr, AuBr, TlBr, PbBr, PtBr2, and Hg2Br2 (19). 

Calcium metal is an excellent reducing agent for production of the less common metals because of the large free energy of formation of its oxides and halides. The following metals have been prepared by the reduction of their oxides or fluorides with calcium hafnium (22), plutonium (23), scandium (24), thorium (25), tungsten (26), uranium (27,28), vanadium (29), yttrium (30), zirconium (22,31), and most of the rare-earth metals (32). 

Several attempts have been made to correlate the adsorptivity of hydrolyzable cations to the composition of the species in aqueous solution (1, 2, 20). In particular, the adsorption of thorium on silver halides indicated a very close relationship between the change in the amount of thorium adsorbed and the concentration of the hydrolyzed soluble species in solution (19). The major difficulty in this type of work is the lack of quantitative data on the hydrolysis of various metal ions. The other uncertainty is with regard to the knowledge of the true surface area of the adsorbent in aqueous solution. This latter information is needed if surface coverages are to be evaluated. 

Thorium forms one series of halides, another one of oxyhalides, and also a series of double or complex halides. In general, stability of these compounds toward heat decreases as die atomic weight of die halogen increases. These compounds are often isostructural with the corresponding compounds of other actinide elements in the (IV) oxidation state. 

Metathetic exchange of alkoxide or phenoxide for halide is possible using either lithium or sodium salts. For instance, thorium tetraalkoxides55 are best obtained from the reaction shown in equation (8). 

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