Tantalum pentafluoride

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Tantalum(V) fluoride
Tantalum(V) fluoride
Identifiers
CAS number 7783-71-3 YesY
PubChem 82218
EC number 232-022-3
RTECS number WW5775000
Jmol-3D images Image 1
Properties
Molecular 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
Structure
Dipole moment 0 D
Hazards
EU classification not listed
R-phrases 34
S-phrases 26-27-28-36/37/39-45
Main hazards HF source
Flash point Non-flammable
Related compounds
Related compounds TaCl5
NbCl5
WF6
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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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.[1] NbF5 is prepared similarly.

Solid and molten TaF5 is tetrameric, consisting of four TaF4 centers linked together via bridging fluoride centers. Gaseous TaF5 adopts the trigonal pyramidal structure with D3h symmetry.[2]

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
.[3] In the presence of fluoride, tantalum pentafluoride forms the anions [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
:[4]

[TaF
7
]2−
+ HF is in equilibrium with [TaF
6
]
+ HF
2

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.[5]

References[edit]

  1. ^ Priest, H. F. “Anhydrous Metal Fluorides” Inorganic Syntheses McGraw-Hill: New York, 1950; Vol. 3, pages 171-183.doi:10.1002/9780470132340.ch47
  2. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  3. ^ Arpad Molnar; G. K. Surya Prakash; Jean Sommer (2009). Superacid Chemistry (2nd ed.). Wiley-Interscience. p. 60. ISBN 0-471-59668-X. 
  4. ^ Anatoly Agulyanski (2004). The chemistry of tantalum and niobium fluoride compounds. Amsterdam: Elsevier. p. 134. ISBN 0-444-51604-2. 
  5. ^ 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