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[edit]

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[edit]

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[edit]

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[edit]

^ "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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