Tungsten(IV) bromide
Chemical compound
From Wikipedia, the free encyclopedia
Tungsten(IV) bromide, also known as tungsten tetrabromide, is an inorganic compound of tungsten and bromine with the chemical formula WBr4.[1] It is a dark, moisture-sensitive solid that serves as a key intermediate and precursor in coordination chemistry for synthesizing quadrivalent tungsten complexes.
| Names | |
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| IUPAC name
tetrabromotungsten | |
| Other names
Tungsten tetrabromide, tungsten(4+) bromide | |
| Identifiers | |
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CompTox Dashboard (EPA) |
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| Properties | |
| WBr4 | |
| Molar mass | 503.46 g/mol |
| Appearance | Dark brown to black crystalline solid |
| Melting point | 240 °C (sublimes) |
| ~240 °C | |
| Reacts with water (hydrolysis) | |
| Structure[1] | |
| orthorhombic | |
a = 8.49 Å, b = 9.29 Å, c = 7.25 Å α = 90°, β = 90°, γ = 90° | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Structure and properties
WBr4 is isomorphous with tungsten(IV) chloride (WCl4), niobium(IV) bromide (NbBr4), and tantalum(IV) bromide (TaBr4).[1] In the solid state, it forms a coordination polymer composed of edge-sharing octahedral units with metal–metal (W-W) bonding interactions along the chain, leading to reduced paramagnetism. The crystal structure is orthorhombic.[1]
When heated under vacuum to 450–500 °C, tungsten(IV) bromide thermally disproportionates into lower halides such as tungsten(II) bromide (WBr2) and volatile higher halides:[1]
- 2 WBr4 → WBr2 + WBr6
Synthesis
Tungsten(IV) bromide can be synthesized via several preparative routes:
Reduction of tungsten(V) bromide
Heating WBr5 with metallic aluminium in a sealed, evacuated tube under a temperature gradient produces crystalline WBr4 via chemical vapor transport:[1]
- 3 WBr5 + Al → 3 WBr4 + AlBr3
Oxidation of tungsten hexacarbonyl
A high-yield solution-phase route involves reacting W(CO)6 directly with elemental bromine (Br2) in an organic solvent:[citation needed]
- W(CO)6 + 2 Br2 → WBr4 + 6 CO
Reactivity
Tungsten(IV) bromide hydrolyzes rapidly upon contact with atmospheric moisture or water.[1] When exposed to trace oxygen at elevated temperatures, it converts to tungsten(VI) oxytetrabromide (WOBr4).
As a Lewis acid, WBr4 reacts with neutral donor ligands to yield 6-coordinate adducts:
- Monodentate ligands: Reacts with acetonitrile, tetrahydrofuran, or triphenylphosphine to yield octahedral adducts such as WBr4(MeCN)2, WBr4(THF)2, and WBr4(PPh3)2.[citation needed]
- Bidentate ligands: Forms chelates with 2,2'-bipyridine (bpy) or 1,2-bis(diphenylphosphino)ethane (dppe) to produce WBr4(bpy) and WBr4(dppe).[citation needed]