LOW-TEMPERATURE SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF 3 NOVEL MAGNESIUM PLATINUM INTERMETALLICS, T-MGPTCXHY, T-MG2PTCXHY, M-MG2PTCXHY

Reactions between catalytically prepared solid or solubilized magnesium hydride (MgH2) and various transition metal species in organic solvents under mild conditions (< 25-degrees-C) can be used to prepare amorphous binary magnesium intermetallics containing hydrogen. Within a particular binary system, a series of crystalline intermetallic compounds can be purposely synthesized by controlling the molar ratio of the reactants in the initial low temperature synthesis step and the subsequent thermal handling. In the magnesium platinum system, three novel compounds, t-MgPtC(x)H(y), t-Mg2PtCxHy and m-Mg2PtCxHy, have been isolated through this route, which were not previously obtained via metallurgical techniques. These crystalline intermetallics were structurally characterized via X-ray powder diffraction. t-MgPtC(x)H(y) crystallizes with a tetragonal cell (P4/mmm: a = 2.966(5), c 3.509(1) angstrom) and the metal atom framework is isostructural with the HgMn structure type t-Mg2PtCxHy crystallizes with a tetragonal cell (I4/mcm: a = 6.3338(3), c = 5.6191(3)angstrom) and the metal atom substructure was refined on the basis of a Al2Cu structural model. m-Mg2PtCxHy reveals a monoclinic unit cell C2/c: a = 7.214(l), b = 7.199(2), c = 6.9008(9) angstrom, beta = 106.05(1). The structure Of m-Mg2PtCxHy was refined in a subcell C2/m: a = 4.2451(4), b = 7.1945(9), c = 2.8200(2) angstrom, beta = 92.638(9) and represents a new distorted variant of the high pressure form of titanium, omega-Ti.