Vanadium pentafluoride

Vanadium(V) fluoride is the inorganic compound with the chemical formula VF₅. It is a colorless volatile liquid.[1] It is a highly reactive compound, as indicated by its ability to fluorinate organic substances .[2]

Vanadium(V) fluoride

Names
IUPAC name Vanadium(V) fluoride
Other names Vanadium pentafluoride
Identifiers
CAS Number	7783-72-4^Y
ECHA InfoCard	100.029.112
PubChem CID	165641
UNII	1GNN7H50UE^Y
Properties
Chemical formula	VF5
Molar mass	145.934
Appearance	colorless solid
Density	2.502 g/cm^3 (solid)
Melting point	19.5 °C (67.1 °F; 292.6 K)
Boiling point	48.3 °C (118.9 °F; 321.4 K)
Related compounds
Other cations	Niobium(V) fluoride Tantalum(V) fluoride
Related Vanadium compounds	Vanadium(V) oxide Vanadium trifluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Properties and structure

The compound is exclusively a monomer in the gas phase.[3] In the gas phase it adopts D_3h symmetric trigonal bipyramidal geometry as indicated by electron diffraction.[4] As a solid, VF₅ forms a polymeric structure with fluoride-bridged octahedral vanadium centers.[3][5]

The formation enthalpy of VF₅ is -1429.4 ± 0.8 kJ/mol.[6]

It is the only known pentahalide of vanadium.

Synthesis

Vanadium pentafluoride can be prepared by fluorination of vanadium metal:[7][1]

2 V + 5 F₂ → 2 VF₅

Alternatively, disproportionation of vanadium tetrafluoride yields equal amounts of the solid trifluoride and the volatile pentafluoride:[8][9][1]

2 VF₄ → VF₃ + VF₅

This conversion is conducted at 650 °C. It can also be synthesized by using elemental fluorine to fluorinate industrial concentrates and raw materials so as to produce VF₅ on an industrial scale. VF₅ can be synthesized from the reaction of raw materials such as metallic Vanadium, ferrovanadium, vanadium (V) oxide and vanadium tetrafluoride with elemental fluorine.[10]

VF₅ ionises in the liquid state as reflected by the high values of Trouton's constant and electrical conductivities.[11]

Characteristics and Reactivity

Interest in this highly corrosive compound began in the fifties when there were extensive studies of its physicochemical properties.[10] It is a powerful fluorinating and oxidizing agent. It oxidizes elemental sulfur to sulfur tetrafluoride:.

S + 4 VF₅ → 4 VF₄ + SF₄

Like other electrophilic metal halides, it hydrolyzes, first to the oxyhalide:

VF₅ + H₂O → VOF₃ + 2 HF

Then to the binary oxide:

2 VOF₃ + 3 H₂O → V₂O₅ + 6 HF

Hydrolysis is accelerated in the presence of base. Despite its tendency to hydrolyze, it can be dissolved in alcohols.

It is a Lewis acid, as illustrated by its formation of the hexafluorovanadate:[12][13][14]

VF₅ + KF → KVF₆

Vanadium pentafluoride is a weaker acid and mainly undergoes oxidative and fluorinating reactions.[15]

The compound fluorinates unsaturated polyfluoroolefins into polyfluoroalkanes.[10]

The compound dissolves without reaction in liquid Cl₂ and Br₂. VF₅ is moderately soluble in HF.

References

1. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 989. ISBN 978-0-08-037941-8.
2. Canterford, J. H.; O'Donnell, Thomas A. (1967-03-01). "Reactivity of transition metal fluorides. IV. Oxidation-reduction reactions of vanadium pentafluoride". Inorganic Chemistry. 6 (3): 541–544. doi:10.1021/ic50049a025. ISSN 0020-1669.
3. Brownstein, S.; Latremouille, G. (1974-06-15). "Complex Fluoroanions in Solution. V. Vanadium Pentafluoride". Canadian Journal of Chemistry. 52 (12): 2236–2241. doi:10.1139/v74-323. ISSN 0008-4042.
4. Hagen, Kolbjoern.; Gilbert, Michael M.; Hedberg, Lise.; Hedberg, Kenneth. (1982-07-01). "Molecular structure of gaseous vanadium pentafluoride, VF5". Inorganic Chemistry. 21 (7): 2690–2693. doi:10.1021/ic00137a031. ISSN 0020-1669.
5. Brownstein, S. (1980-06-01). "The structure of VF5 in solution". Journal of Fluorine Chemistry. 15 (6): 539–540. doi:10.1016/S0022-1139(00)85231-8.
6. Nikitin, M. I.; Zbezhneva, S. G. (2014-12-16). "Thermochemistry of vanadium fluorides: The formation enthalpies of vanadium fluorides". High Temperature. 52 (6): 809–813. doi:10.1134/S0018151X14060108. ISSN 0018-151X.
7. Trevorrow, L. E.; Fischer, J.; Steunenberg, R. K. (1957). "The Preparation and Properties of Vanadium Pentafluoride". Journal of the American Chemical Society. 79 (19): 5167–5168. doi:10.1021/ja01576a023.
8. Ruff, Otto; Lickfett, Herbert (1911). "Vanadinfluoride" (PDF). Berichte der Deutschen Chemischen Gesellschaft. 44 (3): 2539–2549. doi:10.1002/cber.19110440379.
9. Cavell, R. G.; Clark, H. C. (1963). "Thermochemistry of vanadium fluorides". Transactions of the Faraday Society. 59: 2706. doi:10.1039/TF9635902706.
10. Krasil'nikov, V. A.; Andreev, G. G.; Karelin, A. I.; Guzeeva, T. I.; Furin, G. G.; Bardin, V. V.; Avramenko, A. A. (1995-10-17). "ChemInform Abstract: Synthesis and Use of Vanadium Pentafluoride". ChemInform. 26 (42): no. doi:10.1002/chin.199542022. ISSN 1522-2667.
11. Clark, H. C.; Emeléus, H. J. (January 1958). "40. Chemical reactions with vanadium, niobium, and tantalum pentafluorides". J. Chem. Soc. 0: 190–195. doi:10.1039/jr9580000190.
12. Справочник химика / Редкол.: Никольский Б.П. и др.. — 3-е изд., испр. — Л.: Химия, 1971. — Т. 2. — 1168 с. (in Russian)
13. Химическая энциклопедия / Редкол.: Кнунянц И.Л. и др.. — М.: Советская энциклопедия, 1995. — Т. 4. — 639 с. — ISBN 978-5-85270-092-6 (in Russian)
14. Лидин Р.А. и др. Химические свойства неорганических веществ: Учеб. пособие для вузов. — 3-е изд., испр. — М.: Химия, 2000. — 480 с. — ISBN 978-5-7245-1163-6 (in Russian)
15. Fowler, Brian R.; Moss, Kenneth C. (1979-12-01). "An N.M.R. study of the solution chemistry of vanadium pentafluoride". Journal of Fluorine Chemistry. 14 (6): 485–494. doi:10.1016/S0022-1139(00)82524-5.

Other reading

• Arnold F. Holleman, Nils Wiberg: Lehrbuch der Anorganischen Chemie, 102. Auflage, de Gruyter, Berlin 2007, S. 1545, ISBN 978-3-11-017770-1.