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We have determined the structures of two phases of unsolvated Mg(BH4)2, a material of interest for hydrogen storage. One or both phases can be obtained depending on the synthesis conditions. The first, a hexagonal phase with space group P61, is stable below 453 K. Upon heating above that temperature it transforms to an orthorhombic phase, with space group Fddd, stable to 613 K at which point it decomposes with hydrogen release. Both phases consist of complex networks of corner-sharing tetrahedra consisting of a central Mg atom and four BH4 units. The high-temperature orthorhombic phase has a strong antisite disorder in the a lattice direction, which can be understood on the basis of atomic structure. [ABSTRACT FROM AUTHOR]

The article discusses a study on the solution of the crystal structure of the hidden super lattice in isostructural compounds TI2 (SC6H4S) and TI2 (SeC6H4Se) by simulated annealing from high resolution synchrotron X-ray powder diffraction. It also discusses the synthesis of this isostructural compounds by electric conductivity of metal arenethiolate. The interaction of TI-S or TI-Se bonds is also discussed.

Reports that the compounds tetrakis(trimethylsilyl)methane (TC) and tetrakis(trimethylsilyl)silane (TSi) have crystal structures with the molecules in a cubic closed-packed stacking. Space group at room temperature of both structures; Description of an X-ray scattering data by a molecule with approximately sixfold orientational disorder, ruling out structure with free rotating molecules.