ORTHORHOMBIC MG4IRD5 WITH DISORDERED DEUTERIUM DISTRIBUTION

Mg4IrH5 and its deuteride was synthesized by the reaction of magnesium and iridium powders with hydrogen (deuterium) at high pressure (41-10 0 bar) and high temperature (723-783 K). The structure was determined by X-ray and neutron powder diffraction. This compound crystallizes wi th a new structure type with orthorhombic symmetry (space group Imma, cell parameters a = 4.8110(3) angstrom, b = 8.9624(6) angstrom, c = 10 .8970(8) angstrom, Z = 4, hydride, T = 298 K). It contains two deuteri um sites: one is disordered with an occupancy of 75% and surrounds iri dium in a distorted square planar configuration with distances [Ir-D] = 1.69 angstrom; the other is ordered and is coordinated by magnesium in a distorted tetrahedral configuration.