Tantalum(V) fluoride is the

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

with the formula TaF₅. It is one of the principal molecular compounds of tantalum. Characteristic of some other pentafluorides, the compound is volatile but exists as an oligomer in the solid state.

Preparation and structure

It is prepared by treating tantalum metal with

fluorine Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reacti ...

gas. NbF₅ is prepared similarly. Solid and molten TaF₅ is tetrameric, consisting of four TaF₆ centers linked via bridging fluoride centers. Gaseous TaF₅ adopts the trigonal pyramidal structure with D_3h

symmetry Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definit ...

Reactions and derivatives

The tendency of TaF₅ to form clusters in the solid state indicates the Lewis acidity of the monomer. Indeed, TaF₅ reacts with fluoride sources to give the ions , , and . With neutral Lewis bases, such as diethyl ether TaF₅ forms adducts. is used in combination with HF as a catalyst for the alkylation of

alkane In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which ...

s and alkenes and for the protonation of aromatic compounds. The system is stable in reducing environments, unlike . In the presence of fluoride, tantalum pentafluoride forms the anions , , or , depending on the nature of the counterion and the concentration of HF. High concentrations of HF favor the hexafluoride by virtue of the formation of : : + HF + The salts M₃TaF₈ have been crystallized. For K⁺ = M⁺, the crystals consist of anions together with fluoride that does not coordinate to Ta(V). For M⁺ = M⁺, the crystals features . : 260875-ICSD

Relevance to separation of Ta and Nb

In the Marignac process, Nb and Ta are separated by fractional crystallization of K₂TaF₇ from solutions of hydrofluoric acid. Under these conditions, niobium forms K₂NbOF₅, which is more soluble than K₂TaF₇. Reduction of K₂TaF₇ with sodium gives metallic Ta.Klaus Andersson, Karlheinz Reichert, Rüdiger Wolf "Tantalum and Tantalum Compounds" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH. Weinheim.

References

{{fluorine compounds Fluorides Tantalum compounds Metal halides