Tantalum(V) chloride
Tantalum 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.
Structure
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 [Phosphorus pentachloride|].Synthesis
Tantalum pentachloride can be prepared by treating powdered metallic tantalum with chlorine gas at between 170 and 250 °C. This reaction can also be performed using HCl at 400 °C.It can also be prepared by a reaction between tantalum pentoxide and thionyl chloride at 240 °C.
Tantalum pentachloride is commercially available, however samples can be contaminated with tantalum oxytrichloride, formed by hydrolysis. Samples contaminated with niobium pentachloride appear yellow.
Reactions
is electrophilic. It forms adducts with a variety of Lewis bases. It serves as a Lewis acid in Friedel-Crafts reactions.Simple adducts
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:
Chloride displacement reactions
Tantalum pentachloride reacts at room temperature with an excess of triphenylphosphine oxide to give oxychlorides:Hydrolysis, alcoholysis, ammonolysis and related reactions
Anhydrous TaCl5 rapidly 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.