Mg6Ir2H11, a new metal hydride containing saddle-like [IrH4]5 and square-pyramidal [IrH5]-4 hydrido complexes

Mg6Ir2H11 has been synthesised by both hydrogenation of the intermetallic compound Mg3Ir at 20 bar and similar to300 degreesC, and sintering of the elements at similar to500 degreesC under 50 bar hydrogen pressure. Neutron powder diffraction on the deuteride indicates a monoclinic structure (space group P2,/c, Mg6Ir2D11: a=10.226(1), b=19.234(2). c=8.3345(9) Angstrom, beta=91.00(1)degrees. T=20 degreesC) 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 degreesC into Mg3Ir, iridium and a previously unreported intermetallic compound of composition Mg5Ir2. (C) 2002 Elsevier Science B.V. All rights reserved.