On the Volume Chemistry of Solid Compounds: the Legacy of Wilhelm Biltz

For the calculation of the atomic or ionic volumes the Quantum Theory of Atoms In Molecules method was applied. The regions (basins) around the nuclei confined by the zero‐flux surfaces in the electron density gradient are called QTAIM atoms. They are non‐overlapping and completely fill the space. The volume of the basins gives volumes of atoms or ions. The integration of the electron density within the volumina yields effective charges, defining neutral or ionic character of the given QTAIM species. Present investigations refer to metal hydrides, metal nitrides and to intermetallic compounds of the system Al‐Pt. A linear relation between the ionic volumina of hydrogen or nitrogen established according to QTAIM and after Biltz has been found with (homodesmic) binary metal hydrides and binary metal nitrides, but has been observed merely as a trend with stronger deviations for heterodesmic compounds, such as ternary hydrido‐ and nitridometallates A_a[M_mX_x] (A – alkali or alkaline earth metal, M – transition metal and X – H or N). The deviation from linearity for heterodesmic compounds is caused by the different kinds of chemical bonds being present within the [M_mX_x] anions on the one hand and between the anions and the cations on the other hand reflected by the calculated volumes and the QTAIM charges of M and X components. Concerning the intermetallic compounds of the system Al‐Pt, the quantum chemical calculations reveal negative charges for the platinum atoms and positive ones for the aluminium atoms in accordance with their electronegativities. Introducing the variation of the atomic volume with the composition extends the Vegard's approach and gives a non‐linear slope for the concentration dependence of mean atomic volume which explains qualitatively the experimental results.     

Synthese und Kristallstruktur von KMnP und KMnAs

Synthesis and Crystal Structure of KMnP and KMnAs KMnP and KMnAs have been prepared from the elements at 800-°C in a closed system. X-ray investigations suggest a layer-type structure where the manganese atoms are tetrahedrally coordinated by the phosphorus or arsenic atoms. The coordination polyhedra share common edges in two dimensions. The compounds crystallize in the space group P4/nmm with a = 4.275, c = 7.668 Å for KMnP and a = 4.391, c = 7.791 Å for KMnAs, respectively; z = 2. The structural relations to the ternary arsenides with transition metals and lithium, t o Mn₂As, to the oxidehalides of the lanthanides and to ternary sulfides are discussed.     

Alkalimetallrheniumsulfide und -selenide mit [Re6X8]-Baueinheiten

Alkali Metal Rhenium Sulphides and Selenides Containing [Re₆X₈] Clusters The sulphides Rb₄Re₆S₁₃ and Rb₂K₂Re₆S₁₃ were synthesized by the reaction of alkali metal carbonates with rhenium in a stream of H₂S at 800°C. The preparation of the selenides Cs₄Re₆Se₁₃,-Rb₄Re₆Se₁₂, and K₄Re₆Se₁₂ succeeded when a hydrogen atmosphere charged with selenium was used. By combining both reaction methods we obtained mixed crystals of the composition Cs₄Re₆S_9.45Se_3.55. Structural investigations on single crystals revealed atomic arrangements in which [Re₆X₈] clusters are linked threedimensionally by X and X₂ bridges. In the A₄Re₆X₁₂-type a {[Re₆X₈]X_4/2(X₂)_2/2}^4? framework is found whereas the corresponding notation for the A₄Re₆X₁₂-type is {[Re₆X₈]X_2/2(X₂)_4/2}^4?. The dependence of the respective type of framework on the size of the alkali metal ions will be discussed. The diamagnetic behaviour, which was measured in the temperature range between 3.8 and 300 K corresponds with the existence of nearly regular Re₆-octahedra with a 24-electron configuration.     

BaAg2S2, ein Thioargentat im CaAl2Si2-Strukturtyp

BaAg₂S₂, a Thioargentate with the CaAl₂Si₂-Type Structure BaAg₂S₂ could be obtained as crystalline powder by the reaction of barium-bis[dicyanoargentate(I)] in a stream of hydrogensulfid at 500°C. Single crystals grew at 480°C in an evacuated glass ampoule filled with a flux of potassium thiocyanate and powdery BaAg₂S₂ as solid. BaAg₂S₂ crystallises in the trigonal CaAl₂Si₂-typ structure, a = 4.386(1) Å, c = 7.194(2) Å, space group P3 m1, Z = 1. The structure was determined from four-circle diffractometer data. The silver-sulphur distances are discussed with respect to the corresponding distances of the hitherto known alkaline earth-transition metal pnictides, also crystallizing in the CaAl₂Si₂-typ structure.     

Synthese und Struktur von Na2PtH4, einem ternären Hydrid mit quadratisch planaren PtH42−-Baugruppen

Synthesis and Structure of Na₂PtH₄, a Ternary Hydride with Square Planar PtH₄^2? Groups The red violet hydride Na₂PtH₄ is synthesized by the reaction of sodium hydride with platinum in a hydrogen atmosphere at a temperature between 280°C and 310°C. The crystal structure was determined by X-ray and neutron diffraction experiments (Na₂PtD₄) on powdered samples. Na₂PtH₄ crystallizes in a new structure type (a = 5.274(2), c = 6.788(3) Å; space group I4/mmm; Z = 2), which is characterized by planar, diamagnetic PtH₄^2? anions. Structural relations and relative stabilities of the Na₂PtH₄ and the K₂PtCl₄ structure type are to be discussed.     

Complex Transition Metal Hydrides

Compounds having structural units formed by transition metals and hydrogen have only become known fairly recently. Only the synthesis and structural characterization of ternary metal hydrides A_xM_yH_z in which A is an alkali or alkaline-earth metal and M is a transition metal, led to the discovery of anionic complex groups of the form [MH_z]. Although there are obvious structural similarities to the corresponding halides and oxides, the dynamic properties of the hydride ligand are somewhat unusual and are responsible for numerous phase transformations. Transitions throughout the range from saltlike to metallic behavior make us expect interesting physical properties and applications.     

A novel dicationic phenoxaphosphino-modified xantphos-type ligand--a unique ligand specifically designed for a high activity,selectivity and recyclability

A novel phenoxaphosphino-modified ligand has been prepared and successfully employed in the rhodium catalysed hydroformylation of 1-octene in ionic liquids showing unprecedented high selectivity and activity without detectable rhodium or phosphorus leaching during recycling experiments.     

Untersuchungen zum System Platin/Lithium/Wasserstoff

Investigations on the System Platinum/ Lithium/Hydrogen A ternary hydride with the limiting phase composition LiPtH_0.66 is synthesized by the reaction of lithium hydride with platinum at 600°C under a H₂ atmosphere. The structure, determined by X-ray and neutron diffraction experiments, is shown to be a sheetwise ordered, hexagonal close packing of the platinum and lithium atoms in which the hydrogen atoms occupy tetrahedral interstices. Pressure-composition-temperature data were obtained for the reaction 2/(x ? z) LiPtH_x? 2/(x ? z) LiPtH_z + H₂, with LiPtH_z as β-phase and LiPtH_x as ß-phase between 450–590°C, yielding a ΔH value of 134 kJ (mol H₂)^?1 and a value of 149 J (mol H₂)^?1 K^?1.