Tungsten(IV) oxide

Tungsten dioxide is the chemical compound with the formula WO₂. The bronze-colored solid crystallizes in a monoclinic cell. The rutile-like structure features distorted octahedral WO₆ centers with alternate short W–W bonds (248 pm). 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.

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.