The reactions of magnesium atoms with dioxygen and dioxygen/carbon monoxide mixture have been investigated by matrix isolation infrared absorption spectroscopy. Magnesium atoms react with dioxygcn in solid argon to form the inserted MgO2 molecules under UV excitation, which were previously characterized. Annealing allows the dioxygen molecules to diffuse and to react with MgO2 and form the magnesium bisozonide complex, Mg(O-3)(2), which is proposed to be coordinated by two argon atoms in solid argon matrix. The Mg(O-3)(2)(Ar)(2) complex is characterized to have two equivalent side-on bonded ozonide ligands with a D-2h, symmetry. The coordinated argon atoms can be replaced by carbon monoxide to give the magnesium bisozonide dicarbonyl complex, Mg(O-3)(2)(CO)(2),a neutral magnesium carbonyl complex with CO binding to the Mg2+ center.