Molybdenum(IV) oxide

Molybdenum dioxide is the chemical compound with the formula MoO₂. It is a violet-colored solid and is a metallic conductor. It crystallizes in a monoclinic cell, and has a distorted rutile, (TiO₂) crystal structure. In TiO₂ the oxide anions are close packed and titanium atoms occupy half of the octahedral interstices (holes). In MoO₂ the octahedra are distorted, the Mo atoms are off-centre, leading to alternating short and long Mo – Mo distances and Mo-Mo bonding. The short Mo – Mo distance is 251 pm which is less than the Mo – Mo distance in the metal, 272.5 pm. The bond length is shorter than would be expected for a single bond. The bonding is complex and involves a delocalisation of some of the Mo electrons in a conductance band accounting for the metallic conductivity.
MoO₂ can be prepared :

by reduction of MoO₃ with Mo over the course of 70 hours at 800 °C. The tungsten analogue, WO₂, is prepared similarly.

2 MoO₃ + Mo → 3 MoO₂

by reducing MoO₃ with H₂ or NH₃ below 470 °C

Single crystals are obtained by chemical transport using iodine. Iodine reversibly converts MoO₂ into the volatile species MoO₂I₂.

Molybdenum oxide is a constituent of "technical molybdenum oxide" produced during the industrial processing of MoS₂:

2 MoS₂ + 7O₂ → 2MoO₃ + 4SO₂ MoS₂ + 6MoO₃ → 7MoO₂ + 2SO₂ 2 MoO₂ + O₂ → 2MoO₃

MoO₂ has been reported as catalysing the dehydrogenation of alcohols, the reformation of hydrocarbons and biodiesel. Molybdenum nano-wires have been produced by reducing MoO₂ deposited on graphite. Molybdenum oxide has also been suggested as possible anode material for Li-ion batteries.

Mineralogical form of this compound is called tugarinovite, only very rarely found.