Tungsten hexabromide

Tungsten hexabromide, also known as tungsten(VI) bromide, is a chemical compound of tungsten and bromine with the formula WBr₆. It is an air-sensitive dark grey powder that decomposes above 200 °C to tungsten(V) bromide and bromine.^[1][3]

Tungsten hexabromide

Names
Other names Tungsten(VI) bromide
Identifiers
CAS Number	13701-86-5 Y
3D model (JSmol)	Interactive image
ChemSpider	103871330
PubChem CID	14440251
CompTox Dashboard (EPA)	DTXSID101294742
InChI Key: OQVJXQJWYQNWTI-UHFFFAOYSA-H InChI=1S/6BrH.W/h6*1H;/q;;;;;;+6/p-6
SMILES Br[W](Br)(Br)(Br)(Br)Br
Properties
Chemical formula	WBr6
Molar mass	663.264 g/mol
Appearance	Dark grey solid
Density	5.32 g/cm3
Melting point	232 °C (450 °F; 505 K) (decomposition)
Solubility in water	Hydrolysis
Solubility	Soluble in ethanol, ether, carbon disulfide, and ammonia[1]
Structure[2]
Crystal structure	Rhombohedral
Space group	R3
Lattice constant	a = 6.39 Å, c = 17.53 Å
Lattice volume (V)	620.8 Å3
Formula units (Z)	3
Related compounds
Other anions	Tungsten hexafluoride Tungsten hexachloride
Related compounds	Tungsten(V) bromide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Production and reactions

Production of WBr₆ by the reaction of W(CO)₆ and Br₂

Tungsten hexabromide is mainly produced by the reaction of metallic tungsten and bromine at temperatures around 100 °C in a nitrogen atmosphere:^[1][2]

W + 3 Br₂ → WBr₆

Another method of producing this compound is by the reaction of tungsten hexacarbonyl and bromine at room temperature, releasing carbon monoxide.^[4] It can also be produced by the metathesis reaction of boron tribromide and tungsten hexachloride.^[5]

WBr₆ is reduced with elemental antimony at elevated temperatrues, consecutively producing, WBr₅, WBr₄, W₄Br₁₀, W₅Br₁₂, then finally WBr₂ at 350 °C. This reaction produces antimony tribromide as a side product.^[4][6] Any of these bromides can be reverted to the hexabromide by oxidation with bromine at 160 °C.^[7]

Tungsten hexabromide is hydrolyzed in water, producing tungsten pentoxide and releasing bromine.^[1]

Tungsten(VI) oxytetrabromide is produced by the reaction of tungsten hexabromide and tungsten(VI) oxide:^[7]

2 WBr₆ + WO₃ → 3 WOBr₄

Structure

The trigonal crystal structure of WBr₆ consists of isolated WBr₆ octahedra and is isostructural with α-WCl₆.^[2]

References

1. Herbert A. Schaffer; Edgar F. Smith (1896). "Tungsten Hexabromide". Journal of the American Chemical Society. 18 (12): 1098–1100. doi:10.1021/ja02098a015.
2. W. Willing; U. Müller (1987). "Wolframhexabromid". Acta Crystallogr. C (in German). 43 (7): 1425–1426. Bibcode:1987AcCrC..43.1425W. doi:10.1107/S0108270187091625.
3. O. Kaposi; A. Popović; J. Marsel (1977). "Mass spectrometric studies of tungsten bromides and oxybromides". Journal of Inorganic and Nuclear Chemistry. 39 (10): 1809–1815. doi:10.1016/0022-1902(77)80206-6.
4. M. Ströbele; H. -J. Meyer (2012). "Low-temperature preparation of tungsten halide clusters: Crystal structure of the adduct W5Br12 · SbBr3". Russian Journal of Coordination Chemistry. 38 (3): 178–182. doi:10.1134/S1070328412020078. S2CID 94477859.
5. P. M. Druce; M. F. Lappert (1971). "Boron halides as reagents in inorganic syntheses. Part II. A further general method for the preparation of anhydrous bromides and iodides: halogen exchange reactions". Journal of the Chemical Society A: Inorganic, Physical, Theoretical: 3595–3599. doi:10.1039/J19710003595.
6. Markus Ströbele; H.-Jürgen Meyer (2012). "W4Br10 Cluster Intermediates in the Solid State Nucleation of W6Br12". Zeitschrift für anorganische und allgemeine Chemie. 638 (6): 945–949. doi:10.1002/zaac.201200010.
7. P.C. Crouch; G.W.A. Fowles; R.A. Walton (1970). "The high yield synthesis of the tungsten (VI) oxyhalides WOCl4, WOBr4 and WO2Cl2 and some observations on tungsten(VI) bromide and tungsten(V) chloride". Journal of Inorganic and Nuclear Chemistry. 32 (1): 329–333. doi:10.1016/0022-1902(70)80475-4.