Tantalum(V) fluoride

Tantalum(V) fluoride
Names
	Other names tantalum pentafluoride
Identifiers
CAS Number	7783-71-3 ;
3D model (JSmol)	Interactive image;
ChemSpider	74198;
ECHA InfoCard	100.029.111
EC Number	232-022-3;
PubChem CID	82218;
RTECS number	WW5775000;
UNII	QAG1W735WO ;
CompTox Dashboard (EPA)	DTXSID5064833 ;
	InChI Key: YRGLXIVYESZPLQ-UHFFFAOYSA-I; InChI=1S/5FH.Ta/h5*1H;/q;;;;;+5/p-5;
	SMILES F[Ta](F)(F)(F)F;
Properties
Chemical formula	TaF5
Molar mass	275.95 g/mol
Appearance	white powder
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)
Solubility in water	decomposes
Magnetic susceptibility (χ)	+795.0·10−6 cm3/mol
Structure
Dipole moment	0 D
Hazards
	Occupational safety and health (OHS/OSH):
Main hazards	HF source
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H302, H314
Precautionary statements	P260, P261, P264, P270, P271, P280, P301+P312, P301+P330+P331, P302+P352, P303+P361+P353, P304+P312, P304+P340, P305+P351+P338, P310, P312, P321, P322, P330, P363, P405, P501
Flash point	Non-flammable
Related compounds
Related compounds	TaCl5; NbCl5; WF6
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

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

It is prepared by treating tantalum metal with fluorine gas.^[2] 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.^[3]

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
₆]⁻
, [TaF
₇]²⁻
, and [TaF
₈]³⁻
. With neutral Lewis bases, such as diethyl ether TaF₅ forms adducts.

TaF
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.^[4] In the presence of fluoride, tantalum pentafluoride forms the anions [TaF
₈]³⁻
, [TaF
₇]²⁻
, or [TaF
₆]⁻
, 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⁻
₂:^[5]

[TaF
₇]²⁻
+ HF ⇌ [TaF
₆]⁻
+ HF⁻
₂

The salts M₃TaF₈ have been crystallized. For K⁺ = M⁺, the crystals consist of [TaF
₇]²⁻
anions together with fluoride that does not coordinate to Ta(V).^[6] For M⁺ = M⁺, the crystals features [TaF
₈]³⁻
.^[7]

Section of the Na₃TaF₈ 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 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.^[8]

References

^ "Tantalum pentafluoride". pubchem.ncbi.nlm.nih.gov. Retrieved 16 December 2021.
^ Priest, Homer F.; Swinehert, Carl F. (1950-01-01), Audrieth, Ludwig F. (ed.), "Anhydrous Metal Fluorides", Inorganic Syntheses, vol. 3 (1 ed.), Wiley, pp. 171–183, doi:10.1002/9780470132340.ch47, ISBN 978-0-470-13162-6, retrieved 2024-01-22
^ 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 978-0-471-59668-4.
^ Anatoly Agulyanski (2004). The chemistry of tantalum and niobium fluoride compounds. Amsterdam: Elsevier. p. 134. ISBN 0-444-51604-2.
^ Ľubomír Smrčok; Radovan Černý; Miroslav Boča; Iveta Macková; Blanka Kubíková (2010). "K₃TaF₈ from Laboratory X-ray powder data". Acta Crystallographica C. 66 (2): pi16–pi18. Bibcode:2010AcCrC..66I..16S. doi:10.1107/S0108270109055140. PMID 20124670.
^ Langer, V.; Smrčok, L.; Boča, M. (2010). "Redetermination of Na₃TaF₈". Acta Crystallographica C. 66 (9): pi85–pi86. Bibcode:2010AcCrC..66I..85L. doi:10.1107/S0108270110030556. PMID 20814090.
^ 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

[1] "Tantalum pentafluoride". pubchem.ncbi.nlm.nih.gov. Retrieved 16 December 2021.

[2] Priest, Homer F.; Swinehert, Carl F. (1950-01-01), Audrieth, Ludwig F. (ed.), "Anhydrous Metal Fluorides", Inorganic Syntheses, vol. 3 (1 ed.), Wiley, pp. 171–183, doi:10.1002/9780470132340.ch47, ISBN 978-0-470-13162-6, retrieved 2024-01-22

[3] Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.

[4] Arpad Molnar; G. K. Surya Prakash; Jean Sommer (2009). Superacid Chemistry (2nd ed.). Wiley-Interscience. p. 60. ISBN 978-0-471-59668-4.

[agulyanski2004-5] Anatoly Agulyanski (2004). The chemistry of tantalum and niobium fluoride compounds. Amsterdam: Elsevier. p. 134. ISBN 0-444-51604-2.

[6] Ľubomír Smrčok; Radovan Černý; Miroslav Boča; Iveta Macková; Blanka Kubíková (2010). "K₃TaF₈ from Laboratory X-ray powder data". Acta Crystallographica C. 66 (2): pi16–pi18. Bibcode:2010AcCrC..66I..16S. doi:10.1107/S0108270109055140. PMID 20124670.

[7] Langer, V.; Smrčok, L.; Boča, M. (2010). "Redetermination of Na₃TaF₈". Acta Crystallographica C. 66 (9): pi85–pi86. Bibcode:2010AcCrC..66I..85L. doi:10.1107/S0108270110030556. PMID 20814090.

[8] 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

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