3D model (JSmol)
|Molar mass||275.95 g/mol|
|Density||4.74 g/cm3, solid|
|Melting point||96.8 °C (206.2 °F; 369.9 K)|
|Boiling point||229.5 °C (445.1 °F; 502.6 K)|
|Main hazards||HF source|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Tantalum(V) fluoride is the inorganic compound 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
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 [TaF
, and [TaF
. With neutral Lewis bases, such as diethyl ether TaF5 forms adducts.
5 is used in combination with HF as a catalyst for the alkylation of alkanes and alkenes and for the protonation of aromatic compounds. The TaF
5–HF system is stable in reducing environments, unlike SbF
5–HF. In the presence of fluoride, tantalum pentafluoride forms the anions [TaF
, or [TaF
, 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−
+ HF ⇌ [TaF
The salts M3TaF8 have been crystallized. For K+ = M+, the crystals consist of [TaF
anions together with fluoride that does not coordinate to Ta(V). For M+ = M+, the crystals features [TaF
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.
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- Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
- Arpad Molnar; G. K. Surya Prakash; Jean Sommer (2009). Superacid Chemistry (2nd ed.). Wiley-Interscience. p. 60. ISBN 0-471-59668-X.
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- Ľubomír Smrčok, Radovan Černý, Miroslav Boča, Iveta Macková, Blanka Kubíková (2010). "K3TaF8 from Laboratory X-ray powder data". Acta Crystallographica, Section C: Crystal Structure Communications. 66: pi16–pi18. doi:10.1107/S0108270109055140.
- Langer, V.; Smrčok, L.; Boča, M. (2010). "Redetermination of Na3TaF8". Acta Crystallographica, Section C: Crystal Structure Communications. 66: pi85–pi86. doi:10.1107/S0108270110030556.
- 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