Pentamagnesium digallide

Pentamagnesium digallide, also known as magnesium gallide(−V), is a chemical compound in the family of magnesium gallides (MgxGay). This compound has gallium in the rare oxidation state −5 and is produced by splat quenching of a molten mixture of magnesium and gallium metal then heating the resulting substance to 350 °C:
 * 5Mg + 2Ga → Mg5Ga2

It is an unwanted product when magnesium-gallium alloys are exposed to high temperatures.