Tantalum(V) chloride, also known as tantalum pentachloride, is an inorganic compound with the formula . It takes the form of a white powder, which is highly sensitive to moisture. It is synthesised and manipulated under anhydrous conditions, using air-free techniques.
crystallizes in the monoclinic space group C2/m. The ten chlorine atoms define a pair of octahedra that share a common edge. The tantalum atoms occupy the centres of the octahedra and are joined by two chlorine bridging ligands. The dimeric structure is retained in non-complexing solvents and to a large extent in the molten state. In the vapour state, however, is monomeric. This monomer adopts a trigonal bipyramidal structure, like that of .
Tantalum pentachloride can be prepared by treating powdered metallic tantalum with chlorine gas at between 170 and 250 ðC. This reaction can also be performed using HCl at 400 ðC.
It can also be prepared by a reaction between tantalum pentoxide and thionyl chloride at 240 ðC.
Tantalum pentachloride is commercially available, however samples can be contaminated with tantalum(V) oxytrichloride (), formed by hydrolysis. Samples contaminated with niobium pentachloride appear yellow.
is electrophilic. It forms adducts with a variety of Lewis bases. It serves as a Lewis acid in Friedel-Crafts reactions.
forms stable complexes with ethers:.
also reacts with phosphorus pentachloride and phosphoryl chloride, the former as a chloride donor and the latter serves as a ligand, binding through the oxygen:
Tantalum pentachloride reacts with tertiary amines to give adducts:
Tantalum pentachloride reacts at room temperature with an excess of triphenylphosphine oxide to give oxychlorides:
Anhydrous TaCl<sub>5</sub> (Ta<sub>2</sub>Cl<sub>10</sub>) rapidly (but not violently) hydrolyses in water at room temperature.
Tantalum pentachloride reacts with sodium ethoxide to give the pentaethoxide, which also exists as a dimer:
A variety of related alkoxides and mixed chloro-alkoxides are known, e.g. .
Ammonium chloride gives the nitrido complex .
Reduction of tantalum(V) chloride gives anionic and neutral clusters including and .