${\mathrm{Mg}}_2{\mathrm{IrH}}_6$ is a metastable complex metal hydride with a predicted superconducting transition temperature as high as $170\mathrm{K}$ at ambient pressure. Following the synthesis of isomorphic, insulating ${\mathrm{Mg}}_2{\mathrm{IrH}}_5$ at low pressure, higher-pressure studies were conducted to investigate the phase behavior and compound formation in this system. X-ray diffraction and Raman spectroscopic measurements, combined with ab initio calculations, support the formation of cubic ${\mathrm{Mg}}_2{\mathrm{IrH}}_7$ above ca. 40 GPa. This phase may coexist with a related hexagonal hydride with an estimated composition near ${\mathrm{Mg}}_2{\mathrm{IrH}}_5$. Electrical transport measurements suggest that cubic ${\mathrm{Mg}}_2{\mathrm{IrH}}_7$ is insulating, in agreement with ab initio predictions, and persists during room-temperature decompression until $\sim 20\mathrm{GPa}$ before reverting back to cubic ${\mathrm{Mg}}_2{\mathrm{IrH}}_5$. The experimental results support ground-state structure predictions in the Mg-Ir-H system, and the formation of two nearly identical phases with surrounding compositions may open opportunities to access superconducting ${\mathrm{Mg}}_2{\mathrm{IrH}}_6$ through nonequilibrium processing pathways.

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• High-pressure studies
• Synthesis
• Hydrides
• Superconductors