Tungsten(IV) iodide

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Tungsten(IV) iodide (WI4) is an inorganic compound made from tungsten and iodine. Its IUPAC name is Tungsten(IV) iodide, and it is sometimes called tungsten tetraiodide.

Properties
- It forms black triclinic crystals.
- It is insoluble in cold water, diethyl ether, and chloroform, but dissolves in ethanol.
- Molar mass: about 691.46 g/mol.

Preparation
- One route uses tungsten(VI) chloride and hydrogen iodide: WCl6 + 6 HI → WI4 + 6 HCl + I2.
- Another route uses tungsten(IV) chloride and hydroiodic acid: WCl4 + 4 HI → WI4 + 4 HCl.

Chemical behavior
- Decomposition: When heated in vacuum, WI4 breaks down to WI2 and I2 (WI4 → WI2 + I2).
- Hydrolysis: In hot water, WI4 reacts to form WO2 and HI (WI4 + 2 H2O → WO2 + 4 HI).
- Reactions with halogens: WI4 reacts with chlorine or bromine to give WCl4 or WBr4 and I2
- WI4 + 2 Cl2 → WCl4 + 2 I2
- WI4 + 2 Br2 → WBr4 + 2 I2

Summary
WI4 is a black, relatively water-insoluble tungsten-iodine compound that can be made from WCl6 or WCl4 and HI, decomposes on heating in vacuum, hydrolyzes in hot water, and can react with Cl2 or Br2 to form tungsten tetrachloride or tetrabromide.