Physical Properties
Tantalum(V) chloride, also known as tantalum pentachloride, Yellow monoclinic crystals; hygroscopic; critical temperature 494°C; critical volume 402 cm3/mol; can be sublimed without decomposition in chlorine atmosphere; reacts with water; soluble in ethanol, ether and carbon tetrachloride.
Preparation
Tantalum pentachloride is prepared by heating tantalum metal with excess chlorine:
2Ta + 5Cl2 → 2TaCl5
Reactions
Tantalum pentachloride is hydrolyzed by water to form hydrous tantalum pentoxide, Ta2O5•nH2O and hydrochloric acid:
2TaCl5 + 5H2O → Ta2O5 + 10HCl
Reaction with hydrofluoric acid yields tantalum pentafluoride:
TaCl5 + 5HF → TaF5 + 5HCl
Tantalum pentachloride forms adducts with donor solvent molecules. Also, it forms several complexes and organometallic derivatives.
Reactions with alcohols in the presence of an amine forms dinuclear alkoxides. Thus, with ethanol in the presence of diethylamine, the dinuclear tantalum ethoxide, Ta2(OC2H5)10, is obtained.
Reaction with dimethylzinc forms dichlorotrimethyl tantalum, in which three chlorine atoms are substituted with methyl groups:
2TaCl5 + 3Zn(CH3)2 → 2(CH3)3TaCl2 + 3ZnCl2
Reaction with cyclopentadienyl sodium yields bis(cyclopentadienyl) tantalum trichloride:
TaCl5 + 2C5H5 Na → (C5H5)2TaCl3 + 2NaCl
Chemical Properties
Pale-yellow, crystalline powder; highly
reactive. Decomposed by moist air. Soluble in alcohol and potassium hydroxide
solution. Keep well stoppered.
Physical properties
Yellow monoclinic crystals; hygroscopic; density 3.68 g/cm
3; melts at 216°C; vaporizes at 239.4°C; critical temperature 494°C; critical volume 402 cm
3/mol; can be sublimed without decomposition in chlorine atmosphere; reacts with water; soluble in ethanol, ether and carbon tetrachloride.
Uses
Tantalum(V) chloride is used in the preparation of catalyst for the polycyclotrimerizations of alkenediynes, chloro-aryloxide compounds and for the plasma-enhanced atomic layer deposition of tantalum nitride films. It acts as a starting material for new edge-bridged octahedral M6 cluster compounds. It is involved in the preparation of tantalum(V) oxychloride, tantalum pentoxide. It is electrophilic and behaves like a Friedel-Crafts type catalyst, similar to aluminum(III) chloride.
Production Methods
Tantalum pentachloride, TaCl5, forms strongly hydroscopic, needle-shaped white crystals. It is produced on an industrial scale in large tonnage by the chlorination of tantalum scrap or ferrotantalum with NaFeCl4 or by the reductive chlorination of natural ores or synthetic raw materials. High purity TaCl5 is hydrolyzed with steam and thus converted to Ta2O5 of the highest purity. The reduction of TaCl5 with Mg or Al was repeatedly attempted but this thermite-type process never attained any industrial application. TaCl5 is soluble in absolute alcohol, forming the corresponding alkoxides. The alkoxides as well as the chlorides are suitable products for the deposition of tantalum or tantalum pentoxide layers.
Application
Tantalum(V) chloride is an excellent water soluble crystalline Tantalum source for uses compatible with chlorides.
Used to form mixed chloro-aryloxide compounds, such as [Ta(OC6H3-2,6-i-Pr2)2Cl3]2, which form pyridine or phosphine adducts with a distortedsix-coordinate geometry.
Also used as a starting material for new edge-bridged octahedral M6 cluster compounds such as CsErTa6Cl18, for which electron and stability studies were performed.
Used in the preparation of a simple catalyst for the polycyclotrimerizations of alkenediynes.
Used for the plasma-enhanced atomic layer deposition of tantalum nitride films.
Flammability and Explosibility
Non flammable
Safety Profile
Poison by intraperitoneal route. Moderately toxic by ingestion. When heated to decomposition it emits toxic fumes of Cl-.
Purification Methods
Purify it by sublimation in a stream of Cl2. It forms colourless needles when pure (yellow when contaminated with even less than 1% of NbCl5). It is sensitive to H2O; even in conc HCl it decomposes to tantalic acid. It is soluble in EtOH. [Rolsten J Am Chem Soc 80 2952 1958, Brauer in Handbook of Preparative Inorganic Chemistry (Ed Brauer) Academic Press Vol II p 1302 1965.]
