Mg6Ir2H11 has been synthesised by both hydrogenation of the intermetallic compound Mg3Ir at 20 bar and ∼300 °C, and sintering of the elements at ∼500 °C under 50 bar hydrogen pressure. Neutron powder diffraction on the deuteride indicates a monoclinic structure (space group P21/c, Mg6Ir2D11: a=10.226(1), b=19.234(2), c=8.3345(9) Å, β=91.00(1)°, T=20 °C) that is closely related to orthorhombic Mg6Co2H11. It contains a square-pyramidal [IrH5]4− complex and three saddle-like [IrH4]5− complexes of which one is ordered and two are disordered. Five hydride anions H− are exclusively bonded to magnesium. The compound has a red colour, is presumably non-metallic and decomposes under 3 bar argon at 500 °C into Mg3Ir, iridium and a previously unreported intermetallic compound of composition Mg5Ir2