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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.

Solid-gas reactions play an important role in many technologically important processes from ore smelting to hydrogen storage and the synthesis of functional materials. In situ investigations are very useful for unraveling basic steps of such reactions, rationalizing them and gaining control. For investigating time-resolved solid-gas reactions, we have constructed a gas pressure cell for elastic neutron diffraction. By proper orientation of a single-crystal sapphire tube as sample holder, Bragg peaks from the container material can be completely avoided, thus yielding high-quality powder diffraction data with very clean diffraction background. This enables the extraction of high precision crystal structure data as a function of gas pressure and temperature (laser heating) in time-resolved studies. The potential of the gas pressure cell is demonstrated by in situ studies of the reaction of solids with hydrogen, which yielded detailed models of the reaction pathways including high quality crystal structures of reaction intermediates and products. These were used to predict successfully the existence of further metal hydrides, to explain unusual bonding properties, and to optimize the synthesis of metastable compounds.

Two metal-rich compounds, Pd5InP and Pt5InP, were synthesized as phase-pure powders using a high-temperature ampoule technique. According to the Rietveld analysis, they crystallize in the fairly rare Pd5TlAs structure type (tetragonal system, P4/mmm space group, Pearson symbol tP7, with a = 3.9303(5) A, c = 6.9269(1) A, Z = 1, Rp = 0.029, Rb = 0.004 for Pd5InP, and a = 3.9500(1) A, c = 6.9814(3) A, Z = 1, Rp = 0.034, Rb = 0.005 for Pt5InP. For both compounds, main structural units are indium-centered [TM12In] cuboctahedra (TM=Pd, Pt), alternating along the c axis with [TM8P] rectangular prisms of the PtHg2 type. DFT electronic structure calculations and magnetic measurements indicate 3D metallic conductivity and diamagnetic behavior for both compounds. According to the bonding analysis based on the electron localizability indicator topology and charge density, both compounds are intermetallic in nature and feature four-centered interactions of the 3TM+In type between the transition metal and indium atoms in their heterometallic fragments, complemented in the case of platinum by Pt-Pt pairwise interactions. Both compounds do not show any significant hydrogen uptake up to pressures of ca. 7 MPa and temperatures of 700 K.

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, Fd3 m, a = 7.5308(12) A). Orthorhombic β-CaRh2D3.93(5) (own structure type, Pnma, a = 6.0028(3) A, b = 5.6065(3) A, c = 8.1589(5) A) and γ-CaRh2D3.20(10) (β-CaRh2H3.9 type, Pnma, a = 5.9601(10) A, b = 5.4912(2) A, c = 8.0730(11) A) 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 β-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, Pm3 m, a = 3.6512(2) A). The hydrogenation of CaRh2 provides a synthesis route to otherwise not accessible perovskite-type CaRhH3.

The hydrogenation properties of the intermetallic compounds MgPd2 and Pd2Zn, crystallizing in the Co2Si type, were studied by in situ thermal analysis (DSC) under hydrogen pressure. Pd2Zn does not show any reaction with hydrogen while MgPd2 reversibly forms the hydride MgPd2H. Neutron diffraction on the deuterides reveals the compositions MgPd2D0.861(6) (ambient) and MgPd2D0.97(1) [308(2) K, 2.56(5) MPa deuterium] with hydrogen (deuterium) occupying distorted [MgPd5] octahedral voids. Quantum mechanical calculations support the structure models and show the hydrogenation to be exergonic for MgPd2 and endergonic for Pd2Zn. MgPd2H releases hydrogen under normal conditions or vacuum. Heating under hydrogen pressure leads first reversibly to MgPd2H≈0.2 and subsequently irreversibly to MgPd3H≈1 and MgH2. MgPd2, Pd2Zn, and MgPd2H were classified in a structure map. Trends of axial ratio changes upon hydrogenation of TiNiSi type and ZrBeSi type compounds are discussed.

The crystal structure of Pd11Bi2Se2 was determined and refined from X-ray single crystal data (space group Fd 3 ¯ m, a = 12.4879(14) A, Z = 8). In contrast to the earlier reported Pd3(Bi0.6Se0.4), the title compound crystallizes in a 2 × 2 × 2 superstructure of the BiF3 type with ordered bismuth and selenium distribution and an ordered vacancy according to Pd11□Bi2Se2. The vacancy is located at the center of a palladium tetrahedron capped with a bismuth tetrahedron (stella quadrangula). Pd11Bi2Se2 is isopointal to Li13In3 but shows different ordering of the minority components. Pd11Bi2Se2 is inert to water, organic solvents and concentrated hydrochloric acid and its melting point is 905(1) K. It exhibits a very small effective magnetic moment of μeff = 0.0114(2) μB per palladium atom. Pd11Bi2Se2 does not take up hydrogen up to 7.2(2) MPa hydrogen pressure and temperatures up to 703 K. In the electronic structure, the region near the Fermi level is dominated by almost filled Pd 4d-states. Low yet non-zero density of states and a pseudo-gap at the Fermi level might indicate Pd11Bi2Se2 to be a poor metal.

We report on crystal structure data and hydrogenation properties of 24 palladium-rich intermetallic compounds with elements from groups 12–16 of the Periodic Table. Refined crystal structures based on X-ray powder diffraction data are presented for Pd3As (Fe3P type structure) and several members of the Pd5TlAs type structure family. Hydrogenation was studiedin situby differential scanning calorimetry (DSC) under 5.0 MPa hydrogen pressure up to 430 °C. Pd0.75Zn0.25, PdCd, PdHg, Pd2Sn, Pd5Pb3, Pd13Pb9, Pd3As, Pd20Sb7, Pd8Sb3, Pd5Sb2, PdSb, Pd5Bi2, Pd17Se15, Pd4Se, Pd5TlAs, Pd5CdSe, Pd5CdAs, Pd5HgSe, Pd5InAs, Pd8In2Se and Pd3Bi2Se2do not show any sign of hydrogen uptake according to DSC and X-ray diffraction. For Pd3Sn and Pd3Pb a significant hydrogen uptake with unit cell volume increases of 0.4 and 0.6 %, respectively, with a retained structure type of the parent intermetallic was observed. Hydrogenation of Pd5InSe yields Pd3InH≈0.9and a mixture of palladium selenides. Thermal analysis experiments in helium and in hydrogen atmosphere show that this is a multistep reaction with a decomposition of Pd5InSe to Pd3In and a liquid phase and subsequent hydrogenation of Pd3In.

Pd5InSe has been prepared from the elements. The use of iodine as a mineralizing agent enables the synthesis of single-phase powder samples as well as of single crystals. Pd5InSe is stable in cold air, but reacts to give Pd, In2O3 and Pd4Se at 400 °C. The crystal structure of Pd5InSe was determined from single-crystal X-ray diffraction data (space group P4=mmm, a = 4.0255(7), c = 6.972(1) Å, z(Pd2) = 0.28111(8)) and belongs to the Pd5TlAs-type structure with full occupation of all atomic sites. EDX analysis on the single crystal (Pd5.0(1)In0.99(3)Se1.0(1)) confirms the stoichiometric composition. The relationship to the cubic close packing (Cu-type structure), which may be visualized by the crystal chemical formula Pd4PdTlAs⃞, is proven by a Bärnighausen symmetry tree.