Molybdenum dioxide
# Molybdenum dioxide

Molybdenum dioxide is the chemical compound with the formula $MoO_2.$ It is a violet-colored solid and is a metallic conductor. The mineralogical form of this compound is called tugarinovite, and is only very rarely found.

## Structure

It crystallizes in a monoclinic cell, and has a distorted rutile, $(TiO_2)$ crystal structure. In $TiO_2$ the oxide anions are close packed and titanium atoms occupy half of the octahedral interstices (holes). In $MoO_2$ 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.

## Preparation

$MoO_2$ can be prepared :

* by reduction of $MoO_3$ with Mo over the course of 70 hours at 800 °C (1,470 °F). The tungsten analogue, $WO_2,$ is prepared similarly.

    2 $MoO_3$ + Mo → 3 $MoO_2$
* by reducing $MoO_3$ with $H_2$ or $NH_3$ below 470 °C (878 °F)

Single crystals are obtained by chemical transport using iodine. Iodine reversibly converts $MoO_2$ into the volatile species $MoO_2I_2.$

## Uses

Molybdenum dioxide is a constituent of "technical molybdenum trioxide" produced during the industrial processing of $MoS_2:$

    2 $MoS_2$ + 7 $O_2$ → 2 $MoO_3$ + 4 $SO_2$
    $MoS_2$ + 6 $MoO_3$ → 7 $MoO_2$ + 2 $SO_2$
    2 $MoO_2$ + $O_2$ → 2 $MoO_3$

$MoO_2$ has been reported as catalysing the dehydrogenation of alcohols, the reformation of hydrocarbons and biodiesel. Molybdenum nano-wires have been produced by reducing $MoO_2$ deposited on graphite. Molybdenum dioxide has also been suggested as possible anode material for Li-ion batteries.

