Tungsten(IV) bromide

Tungsten(IV) bromide, also known as tungsten tetrabromide, is an inorganic compound of tungsten and bromine with the chemical formula . It is a dark, moisture-sensitive solid that serves as a key intermediate and precursor in coordination chemistry for synthesizing quadrivalent tungsten complexes.

Structure and properties

is isomorphous with tungsten(IV) chloride (), niobium(IV) bromide (), and tantalum(IV) bromide (). 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.

When heated under vacuum to 450–500 °C, tungsten(IV) bromide thermally disproportionates into lower halides such as tungsten(II) bromide () and volatile higher halides:

Synthesis

Tungsten(IV) bromide can be synthesized via several preparative routes:

Reduction of tungsten(V) bromide

Heating with metallic aluminium in a sealed, evacuated tube under a temperature gradient produces crystalline via chemical vapor transport:

Oxidation of tungsten hexacarbonyl

A high-yield solution-phase route involves reacting directly with elemental bromine () in an organic solvent:

Reactivity

Tungsten(IV) bromide hydrolyzes rapidly upon contact with atmospheric moisture or water. When exposed to trace oxygen at elevated temperatures, it converts to tungsten(VI) oxytetrabromide ().

As a Lewis acid, reacts with neutral donor ligands to yield 6-coordinate adducts:

• Monodentate ligands: Reacts with acetonitrile, tetrahydrofuran, or triphenylphosphine to yield octahedral adducts such as , , and .
• Bidentate ligands: Forms chelates with 2,2'-bipyridine () or 1,2-bis(diphenylphosphino)ethane () to produce and .