Tantalum -chloride TaCl

Tantalum Trichloride, TaCls, is prepared by reducing the pentachloride with aluminium in the presence of aluminium chloride and heating the product to between 350° and 400° C. It is a dark green substance which yields intensely green aqueous solutions without evolution of hydrogen. These solutions are fairly stable, and oxidise only slowly on being exposed to air the rate of oxidation is accelerated by the presence of alkali and checked by the addition of acids. 

The reaction temperature of 500—600°C is much lower than that required for the reductive chlorination. The volatile chlorides evolve from the molten salt bath. The boiling points of NbCl, TaCl, and WOCl He between 228 and 248°C. These compounds must therefore be separated by means of a distillation column. The chlorination of ferroalloys produces very pure tantalum pentachloride in toimage quantities. The TaCl contains less than 5 )J.g Nb/g Ta, and other metallic impurities are only amount to 1—2 lg/g Ta. 

The most important starting materials for organometallic complexes of niobium and tantalum are their pentachlorides, NbCls and TaCls. The commercially available pentachlorides can be sublimed if further purification is necessary. They are commonly used for access to both high-valency and low-valency compounds. The crystal structure of NbCl5 consists of dimeric Nb2Cl owith two chlorides bridging as shown in Scheme 7.8, and the Ta analogue is presumed to have a similar structure. In non-... 

---