Tantalum(V) fluoride

Tantalum(V) fluoride

Tantalum(V) fluoride Tantalum(V) fluoride
Names
Other names tantalum pentafluoride
Identifiers
CAS Number	7783-71-3 checkY
3D model (JSmol)	Interactive image
ChemSpider	74198
ECHA InfoCard
EC Number	232-022-3
E number
PubChem CID	82218
RTECS number	WW5775000
UNII	QAG1W735WO checkY
CompTox Dashboard (EPA)	{{#property:P3117}}
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	275.93990 g·mol−1
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	GHS05: CorrosiveGHS07: Exclamation mark
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
Other anions	Tantalum(V) chloride Tantalum(V) bromide Tantalum(V) iodide
Other cations	Vanadium pentafluoride Niobium(V) fluoride Protactinium(V) fluoride
Related compounds	Tungsten hexafluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). checkY verify (what is checkY☒N ?) 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 a tetramer in the solid state.

Preparation and structure

TaF₅ is prepared by treating tantalum metal with fluorine gas.

2 Ta + 5 F₂ → 2 TaF₅

NbF₅ is prepared similarly.

Solid and molten TaF₅ is tetrameric, consisting of four octahedral TaF₆ centers linked via bridging fluoride centers. Gaseous TaF₅ is monomeric and adopts the trigonal bipyramidal structure with D_3h symmetry.

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 [TaF₆]⁻ (hexafluorotantalate(V)), [TaF₇]²⁻ (heptafluorotantalate(V)), and [TaF₈]³⁻ (octafluorotantalate(V)). With neutral Lewis bases, such as diethyl ether, TaF₅ forms adducts.

TaF₅ is used in combination with HF as a catalyst for the alkylation of alkanes and alkenes and for the protonation of aromatic compounds. The TaF₅–HF system is stable in reducing environments, unlike SbF₅–HF. In the presence of fluoride, tantalum pentafluoride forms the anions [TaF₈]³⁻, [TaF₇]²⁻, or [TaF₆]⁻, 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 [HF₂]⁻:

[TaF₇]²⁻ + HF ⇌ [TaF₆]⁻ + [HF₂]⁻

The salts M₃TaF₈ have been crystallized. For M = K, the crystals consist of [TaF₇]²⁻ anions together with fluoride that does not coordinate to Ta(V), and the salt is actually potassium fluoride heptafluorotantalate(V) (K⁺)₃[TaF₇]²⁻F⁻. For M = Na, the crystals features [TaF₈]³⁻, and the salt is sodium octafluorotantalate(V) (Na⁺)₃[TaF₈]³⁻.

File:260875-ICSD.png

Section of the Na₃[TaF₈] 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 K₂[TaF₇] from solutions of hydrofluoric acid. Under these conditions, niobium forms K₂[NbOF₅], which is more soluble than K₂[TaF₇]. Reduction of K₂[TaF₇] with sodium gives metallic Ta.