Nickel - p-block metal mixed chalcogenides based on AuCu3-type fragments: iodine-assisted synthesis as a way of obtaining new structures.

Two new mixed nickel-gallium chalcogenides, Ni9.39Ga2S2 and Ni5.80GaTe2, and a new mixed nickel-indium telluride, Ni5.78InTe2, have been synthesized by a high-temperature ampoule route with the addition of iodine, and characterized from single-crystal or powder diffraction data. They belong to the relatively uncommon Ni7-xMQ2/Ni10-xM2Q2 type of structures (M = Ge, Sn, Sb, In), and are built from p-block metal-centered nickel cuboctahedra, alternating along the c axis with defective Cu2Sb-type nickel-chalcogen ones. Both tellurium-containing compounds show a small degree of orthorhombic distortion with respect to the idealized tetragonal structure, only detectable in the powder diffraction data. No phase transition to the tetragonal structure was detected for Ni5.80GaTe2 by the in situ powder diffraction measurements from room temperature to 550 °C. DFT calculations show close relationships of electronic structures of these ternary compounds to their parent intermetallics, Ni3M (M = Ga, In). Metallic conductivity and paramagnetic properties are predicted for all three with the latter confirmed by magnetic measurements. The bonding patterns, investigated via the ELF topological analysis, show multi-centered nickel - p-block metal bonds in the AuCu3-type fragments and pairwise covalent interactions in the nickel-chalcogen fragments. Both Ni7-xMTe2 compounds showed no structural or compositional changes upon high-temperature mid-pressure hydrogenation.

From the Laves Phase CaRh2 to the Perovskite CaRhH3-in Situ Investigation of Hydrogenation Intermediates CaRh2H x.

The hydrogenation properties of the cubic Laves phase CaRh2 and the formation of the perovskite CaRhH3 were studied by in situ thermal analysis (differential scanning calorimetry), sorption experiments, and in situ neutron powder diffraction. Three Laves phase hydrides are formed successively at room temperature and hydrogen gas pressures up to 5 MPa. Cubic α-CaRh2H0.05 is a stuffed cubic Laves phase with statistically distributed hydrogen atoms in tetrahedral [Ca2Rh2] voids (ZrCr2H3.08 type, Fd3̅ m, a = 7.5308(12) Å). Orthorhombic ß-CaRh2D3.93(5) (own structure type, Pnma, a = 6.0028(3) Å, b = 5.6065(3) Å, c = 8.1589(5) Å) and γ-CaRh2D3.20(10) (ß-CaRh2H3.9 type, Pnma, a = 5.9601(10) Å, b = 5.4912(2) Å, c = 8.0730(11) Å) are low-symmetry variants thereof with hydrogen occupying distorted tetrahedral [Ca2Rh2] and trigonal bipyramidal [Ca3Rh2] voids. Hydrogen sorption experiments show the hydrogenation to take place already at 0.1 MPa and to yield ß-CaRh2H3.8(2). At 560 K and 5 MPa hydrogen pressure the Laves phase hydride decomposes kinetically controlled to nanocrystalline rhodium and CaRhD2.93(2) (CaTiO3 type, Pm3̅ m, a = 3.6512(2) Å). The hydrogenation of CaRh2 provides a synthesis route to otherwise not accessible perovskite-type CaRhH3.