Magnesium peroxide
Magnesium peroxide (MgO2) is an odorless fine powder peroxide with a white to off-white color. It is similar to calcium peroxide because magnesium peroxide also releases oxygen by breaking down at a controlled rate with water. Commercially, magnesium peroxide often exists as a compound of magnesium peroxide and magnesium hydroxide.
Structure
O2, similarly to N2, has the ability to bind either side-on or end-on. The structure of MgO2 has been calculated as a triangular shape with the O2 molecule binding side-on to the magnesium. This arrangement is a result of the Mg+ donating charge to the oxygen and creating a Mg2+O22−. The bond between to O2 and the magnesium atom has an approximate dissociation energy of 90 kJ mol−1.
In the solid state, MgO2 has a cubic pyrite-type crystal structure with 6-coordinate Mg2+ ions and O22− peroxide-groups, according to experimental data and evolutionary crystal structure prediction, the latter predicting a phase transition at the pressure of 53 GPa to a tetragonal structure with 8-coordinate Mg2+ ions. While at normal conditions MgO2 is a metastable compound (less stable than MgO+1/2O2), at pressures above 116 GPa it is predicted to become thermodynamically stable in the tetragonal phase. This theoretical prediction has been experimentally confirmed via synthesis in a laser-heated diamond anvil cell.