Tantalum(V) fluoride

Preparation and structure

is prepared by treating tantalum metal with fluorine gas.

:

is prepared similarly.

Solid and molten is tetrameric, consisting of four octahedral centers linked via bridging fluoride centers. Gaseous is monomeric and adopts the trigonal bipyramidal structure with D3h symmetry.

Reactions and derivatives

The tendency of to form clusters in the solid state indicates the Lewis acidity of the monomer. Indeed, reacts with fluoride sources to give the ions (hexafluorotantalate(V)), (heptafluorotantalate(V)), and (octafluorotantalate(V)). With neutral Lewis bases, such as diethyl ether, forms adducts.

is used in combination with HF as a catalyst for the alkylation of alkanes and alkenes and for the protonation of aromatic compounds. The –HF system is stable in reducing environments, unlike –HF.{{cite book | url-access = limited

: The salts have been crystallized. For M = K, the crystals consist of anions together with fluoride that does not coordinate to Ta(V), and the salt is actually potassium fluoride heptafluorotantalate(V) . For M = Na, the crystals features , and the salt is sodium octafluorotantalate(V) . :[[File:260875-ICSD.png|298px|thumb|left|Section of the structure (Ta = turquoise, F = green).]]

Relevance to separation of Ta and Nb

In the Marignac process, Nb and Ta are separated by fractional crystallization of from solutions of hydrofluoric acid. Under these conditions, niobium forms , which is more soluble than . Reduction of with sodium gives metallic Ta.

References

References

1. "Tantalum pentafluoride".
2. (1950-01-01). "Anhydrous Metal Fluorides". Wiley.
3. Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. {{ISBN. 0-12-352651-5.
4. Ľubomír Smrčok. (2010). "K₃TaF₈ from Laboratory X-ray powder data". Acta Crystallographica C.
5. (2010). "Redetermination of Na₃TaF₈". Acta Crystallographica C.
6. Klaus Andersson, Karlheinz Reichert, Rüdiger Wolf "Tantalum and Tantalum Compounds" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH. Weinheim. {{doi. 10.1002/14356007.a26_071