Tungsten diiodide (WI₂) has good stability at room temperature but readily reacts chemically at high temperatures and in the presence of oxygen. Tungsten diiodide is an inorganic compound with the following chemical properties.

Tungsten Diiodide is an inorganic compound with the molecular formula WI₂ and a relative molecular mass of 437.7. It is a metal salt of tungsten and hydroiodic acid, characterized by black or dark brown crystals, usually in powder or lump form. Tungsten diiodide has good solubility in alkalis but is insoluble in cold water, ethanol, and carbon disulfide. It has a density of 6.79 g/cm³ and a melting point of about 300°C, which allows it to remain stable at everyday ambient temperatures.

Tungsten diiodide is a transition crystal. Transitional crystals are different from many substances in nature with regular geometrical shapes, such as ionic crystals, molecular crystals, atomic crystals, and metal crystals. The inter-particle role of the lattice junctions of the transitional crystals has changed, and the interactions between particles of the crystalline structure and the nature of the crystal between the different types of crystalline forms, which is difficult to be classified as any of the above-mentioned typical crystals, and there are a lot of actual crystals belonging to the transitional crystals.

The solubility of tungsten diiodide has no specific pattern. For inorganic solvents, tungsten diiodide is soluble in alkali but insoluble in water at room temperature; for organic solvents, tungsten diiodide is insoluble in ethanol and carbon disulfide (CS₂).