Tungsten(IV) oxide
Other names	Tungsten dioxide
Identifiers
CAS number	12036-22-5 Y
Properties
Molecular formula	WO2
Molar mass	215.84 g/mol
Appearance	bronze solid
Density	10.8 g/cm3
Melting point	1700 °C decomp.
Solubility in water	insoluble
Magnetic susceptibility	5.7 × 10−5 cm3/mol
Structure
Crystal structure	Distorted rutile, (monoclinic), mP12, Space group P21/c, No 14
Hazards
EU Index	Not listed
Flash point	Non-flammable
Related compounds
Other anions	Tungsten disulfide
Other cations	Chromium(IV) oxide Molybdenum(IV) oxide
Related tungsten oxides	Tungsten(III) oxide Tungsten(VI) oxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Tungsten dioxide is the chemical compound with the formula WO₂. The bronze-colored solid crystallizes in a monoclinic cell.^[1] The rutile-like structure features distorted octahedral WO₆ centers with alternate short W–W bonds (248 pm).^[1] Each tungsten center has the d² configuration, which gives the material a high electrical conductivity.

WO₂ is prepared by reduction of WO₃ with tungsten powder over the course of 40 hours at 900 °C. An intermediate in this reaction is the partially reduced, mixed valence species W₁₈O₄₉.

2 WO₃ + W → 3 WO₂

The molybdenum analogue MoO₂ is prepared similarly. Single crystals are obtained by chemical transport technique using iodine. Iodine transports the WO₂ in the form of the volatile species WO₂I₂.^[2]

[edit] References

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