Viktor Hlukhyy

Polar Intermetallic Compounds as Catalysts for Hydrogenation Reactions: Synthesis, Structures, Bonding, and Catalytic Properties of Ca1−xSrxNi4Sn2 (x=0.0, 0.5, 1.0) and Catalytic Properties of Ni3Sn and Ni3Sn2

The potential of polar intermetallic compounds to catalyze hydrogenation reactions was evaluated. The novel compounds CaNi4Sn2, SrNi4Sn2, and Ca(0.5)Sr(0.5)Ni(4)Sn(2) were tested as unsupported alloys in the liquid-phase hydrogenation of citral. Depending on the reaction conditions, conversions of up to 21.0 % (253 K and 9.0 MPa hydrogen pressure) were reached. The binary compounds Ni3Sn and Ni3Sn2 were also tested in citral hydrogenation under the same conditions. These materials gave conversions of up to 37.5 %. The product mixtures contained mainly geraniol, nerol, citronellal, and citronellol. The isotypic stannides CaNi4Sn2, Ca(0.5)Sr(0.5)Ni4Sn2, and SrNi4Sn2 were obtained by melting mixtures of the elements in an arc-furnace under an argon atmosphere. Single crystals were synthesized in tantalum ampoules using special temperature modes. The novel structures were established by single-crystal X-ray diffraction. They crystallize in the tetragonal space group I4/mcm with parameters: a=7.6991(7), c=7.8150(8) A, wR2=0.034, 162 F(2) values, 14 variable parameters for CaNi4Sn2; a=7.7936(2), c=7.7816(3) A, wR2=0.052, 193 F(2) values, 15 variable parameters for Ca(0.5)Sr(0.5)Ni4Sn2; and a=7.8916(4), c=7.7485(5) A, wR2=0.071, 208 F(2) values, 14 variable parameters for SrNi4Sn2. The Ca(1-x)Sr(x)Ni(4)Sn(2) (x=0.0, 0.5, 1.0) structures can be represented as a stuffed variant of the CuAl2 type by the formal insertion of one-dimensional infinite Ni-cluster chains [Ni4] into the Ca(Sr)Sn2 substructure. The Ni and Sn atoms form a three-dimensional infinite [Ni4Sn2] network in which the Ca or Sr atoms fill distorted octagonal channels. The densities of states obtained from TB-LMTO-ASA calculations show metallic character for both compounds.

The Neat Ternary Solid K5−xCo1−xSn9 with Endohedral [Co@Sn9]5− Cluster Units: A Precursor for Soluble Intermetalloid [Co2@Sn17]5− Clusters

A new type of Zintl phase is presented that contains endohedrally filled clusters and that allows for the formation of intermetalloid clusters in solution by a one-step synthesis. The intermetallic compound K(5-x)Co(1-x)Sn(9) was obtained by the reaction of a preformed Co-Sn alloy with potassium and tin at high temperatures. The diamagnetic saltlike ternary phase contains discrete [Co@Sn(9)](5-) clusters that are separated by K(+) ions. The intermetallic compound K(5-x)Co(1-x)Sn(9) readily and incongruently dissolves in ethylenediamine and in the presence of 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (2.2.2-crypt), thereby leading to the formation of crystalline [K([2.2.2]crypt)](5)[Co(2)Sn(17)]. The novel polyanion [Co(2)Sn(17)](5-) contains two Co-filled Sn(9) clusters that share one vertex. Both compounds were characterized by single-crystal X-ray structure analysis. The diamagnetism of K(5-x)Co(1-x)Sn(9) and the paramagnetism of [K([2.2.2]crypt)](5)[Co(2)Sn(17)] have been confirmed by superconducting quantum interference device (SQUID) and EPR measurements, respectively. Quantum chemical calculations reveal an endohedral Co(1-) atom in an [Sn(9)](4-) nido cluster for [Co@Sn(9)](5-) and confirm the stability of the paramagnetic [Co(2)Sn(17)](5-) unit.

Synthesis, structure, and electronic properties of 4H-germanium

Reinvestigation of the reaction of Li7Ge12 with benzophenone in tetrahydrofuran solution affords the metastable crystalline germanium allotrope allo-Ge, which transforms into another allotrope, 4H-Ge, upon annealing at temperatures between 150 and 300 °C. When annealing 4H-Ge above 400 °C the ground state modification α-Ge is obtained. The crystal structure of 4H-Ge was refined from powder X-ray diffraction data (space group P63/mmc (no. 194), a = 3.99019(4) and c = 13.1070(2) A, Z = 8) and the sequence of phase transitions from allo-Ge to α-Ge was monitored by temperature-dependent powder X-ray diffraction experiments. Electrical resistivity measurements and quantum-mechanical calculations show that 4H-Ge is a semiconductor, which is in contrast to previous theoretical predictions. The Raman spectrum of 4H-Ge displays three bands at 299, 291, and 245 cm−1 which are assigned to E1g, E2g and A1g modes, respectively, and relate to the optic mode in α-Ge.

Endohedrally Filled [Ni@Sn9]4− and [Co@Sn9]5− Clusters in the Neat Solids Na12Ni1−xSn17 and K13−xCo1−xSn17: Crystal Structure and 119Sn Solid‐State NMR Spectroscopy

A systematic approach to the formation of endohedrally filled atom clusters by a high-temperature route instead of the more frequent multistep syntheses in solution is presented. Zintl phases Na12Ni(1-x)Sn17 and K(13-x)Co(1-x)Sn17, containing endohedrally filled intermetalloid clusters [Ni@Sn9](4-) or [Co@Sn9](5-) beside [Sn4](4-), are obtained from high-temperature reactions. The arrangement of [Ni@Sn9](4-) or [Co@Sn9](5-) and [Sn4](4-) clusters, which are present in the ratio 1:2, can be regarded as a hierarchical replacement variant of the hexagonal Laves phase MgZn2 on the Mg and Zn positions, respectively. The alkali-metal positions are considered for the first time in the hierarchical relationship, which leads to a comprehensive topological parallel and a better understanding of the composition of these compounds. The positions of the alkali-metal atoms in the title compounds are related to the known inclusion of hydrogen atoms in the voids of Laves phases. The inclusion of Co atoms in the {Sn9} cages correlates strongly with the number of K vacancies in K(13-x)Co(1-x)Sn17 and K(5-x)Co(1-x)Sn9, and consequently, all compounds correspond to diamagnetic valence compounds. Owing to their diamagnetism, K(13-x)Co(1-x)Sn17, and K(5-x)Co(1-x)Sn9, as well as the d-block metal free binary compounds K12Sn17 and K4Sn9, were characterized for the first time by (119)Sn solid-state NMR spectroscopy.

Extreme differences in oxidation states: synthesis and structural analysis of the germanide oxometallates A10[Ge9]2[WO4] as well as A(10+x)[Ge9]2[W(1–x)Nb(x)O4] with A = K and Rb containing [Ge9]4- polyanions.

Semitransparent dark-red or ruby-red moisture- and air-sensitive single crystals of A(10+x)[Ge(9)](2)[W(1-x)Nb(x)O(4)] (A = K, Rb; x = 0, 0.35) were obtained by high-temperature solid-state reactions. The crystal structure of the compounds was determined by single-crystal X-ray diffraction experiments. They crystallize in a new structure type (P2(1)/c, Z = 4) with a = 13.908(1) Å, b = 15.909(1) Å, c = 17.383(1) Å, and β = 90.050(6)° for K(10.35(1))[Ge(9)](2)[W(0.65(1))Nb(0.35(1))O(4)]; a = 14.361(3) Å, b = 16.356(3) Å, c = 17.839(4) Å, and β = 90.01(3)° for Rb(10.35(1))[Ge(9)](2)[W(0.65(1))Nb(0.35(1))O(4)]; a = 13.8979(2) Å, b = 15.5390(3) Å, c = 17.4007(3) Å, and β = 90.188(1)° for K(10)[Ge(9)](2)WO(4); and a = 14.3230(7) Å, b = 15.9060(9) Å, c = 17.8634(9) Å, and β = 90.078(4)° for Rb(10)[Ge(9)](2)WO(4). The compounds contain discrete Ge(9)(4-) Wades nido clusters and WO(4)(2-) (or NbO(4)(3-)) anions, which are packed according to a hierarchical atom-to-cluster replacement of the Al(2)Cu prototype and are separated by K and Rb cations, respectively. The alkali metal atoms occupy the corresponding tetrahedral sites of the Al(2)Cu prototype. The amount of the alkali metal atoms on these diamagnetic compounds corresponds directly to the amount of W substituted by Nb. Thus, the transition metals W and Nb appear with oxidation numbers +6 and +5, respectively, in the vicinity of a [Ge(9)](4-) polyanion. The crystals of the mixed salts were further characterized by Raman spectroscopy. The Raman data are in good agreement with the results from the X-ray structural analyses.

At the Border of Intermetallic Compounds and Transition-Metal Oxides: Crystal Intergrowth of the Zintl Phase Cs4Ge9 and Cs2WO4 or Cs3VO4 as well as Nine-Atom Cluster Relocation in the Solid State†

In recent years significant progress in the research on nineatom clusters of germanium has been made. Nine-atom clusters E9 of group 14 elements are species of captivating beauty and simplicity, which can be regarded as small charged element units that open new possibilities for chemical reactions and the development of nanoscaled materials. The isolated clusters Ge9 are well-known in solution and have been stabilized with a variety of counter ions and as solvates, however, in neat solids they are characterized only in a few binary intermetallic phases such as A4Ge9 [3] and A12Ge17 [4] (A = Na, K, Rb, and Cs), in which they mostly show a strong structural disorder. These compounds represent typical saltlike intermetallic compounds, and their solubility in polar solvents makes them valuable precursors for subsequent chemical reactions. Most interesting to materials chemists is the oxidation reaction of [Ge9] 4 clusters which leads to the formation of ([Ge9] 2 )n oligomers and polymers (n = 2, 3, 4, and 1, respectively). A [Ge45] anion has been found to complex Au atoms, and full oxidation leads to the crystalline modification of clathrate-II-type germanium. 7] Further stable Ge modifications based on Ge9 clusters as building blocks are predicted from theoretical calculations. Although deltahedral germanium Zintl anions have been known for a long time and have intensively been studied in solution, their chemistry in the solid state is almost unexplored. The formation of the few reported double salts containing deltahedral Zintl clusters shows, however, Zintl anions to form rather unusual compounds. In the tetrelide–tetrelate compounds Cs10[Si4][Si3O9] and Rb14[E4][Si6O17] (E = Si, Ge) negative and five-fold positive oxidation states of the tetrel elements simultaneously appear. Unfortunately, it was not possible to expand this compound family in which bare element cluster anions are stable in the presence of the respective oxide. Therefore, we investigated the chemical behavior of germanium Zintl clusters in the presence of transition-metal oxides. An energetically high-lying HOMO of the Zintl clusters might be combined with a low-lying conduction band of the transition-metal oxide such as it appears, for example, in tungsten bronzes. In the course of our exploration of the reactions of deltahedral germanium Zintl anions with oxometallates in solid-state reactions, we found synthetic access to a series of novel intergrowth structures containing the reduced nido cluster [Ge9] 4 and oxidized transition metals, which are generally reduced more easily than silicates. We describe here the synthesis, crystal structure, and spectroscopic properties of the compounds Cs10[Ge9]2[WO4] and Cs11[Ge9]2[VO4] containing [Ge9] 4 clusters and oxometallate anions [MO4] x . The extremely airand moisture-sensitive ruby-red single crystals of the title compounds have been obtained by reaction of mixtures of Cs4Ge9 and Cs2WO4 (Cs3VO4), or by the reaction of mixtures of Cs4Ge9, WO3 (V2O5) and HgO (as a mere oxygen provider) with elemental Cs in sealed niobium containers. We show here, that ion packing in the new structures allows to adapt the alkali metal content to the charge of the anions WO4 2 or VO3 3 and probably other anions. Cs10[Ge9]2[WO4] and Cs11[Ge9]2[VO4] crystallize in the space group P21/c. [13] From a crystallographic point of view the former crystallizes in a new structure type, whereas the latter can be considered as the filled structure variant of the former with one additional Cs atom and neglecting the different cluster orientations (Figure 1a,b). Cs10[Ge9]2[WO4] and Cs11[Ge9]2[VO4] both contain two crystallographically independent Ge9 clusters (A and B) and oxo-bonded WO4 2 and VO4 3 anions (C), respectively, in the stacking sequence ACBCA. The Raman spectrum of Cs10[Ge9]2[WO4] (Figure 2) shows the typical signals for nine-atom Ge clusters and tetrahedral WO4 including the very strong breathing mode around 221 cm , and further bands at around 163 and 154 cm 1 for the Ge9 unit. [4a, 14] However, an intense lowrange peak at 54 cm 1 has been observed for the first time for the Ge9 cluster in this study which is attributed to a librational mode of the cluster. The peaks assigned to the WO4 2 anion around 320 and 916 cm 1 are in good agreement with those reported in the literature. The substitution of WO4 2 in Cs10[Ge9]2[WO4] for VO4 3 to give Cs11[Ge9]2[VO4] is counterbalanced by one additional Cs position in the structure. Therefore, according to the ratio of Cs cations to germanide cluster and oxometallate anions, the clusters in both structures are clearly four-fold negatively charged. The expected diamagnetism for the species [Ge9] 4 , WO4 2 , and VO4 3 is confirmed by the negative values of the [*] Dr. V. Hlukhyy, Prof. Dr. T. F. F ssler Departement Chemie, Technische Universit t M nchen Lichtenbergstr. 4, 85747 Garching (Germany) E-mail: thomas.faessler@lrz.tum.de

From One to Three Dimensions: Corrugated ∞1[NiGe] Ribbons as a Building Block in Alkaline Earth Metal Ae/Ni/Ge Phases with Crystal Structure and Chemical Bonding in AeNiGe (Ae = Mg, Sr, Ba)

The new equiatomic nickel germanides MgNiGe, SrNiGe, and BaNiGe have been synthesized from the elements in sealed tantalum tubes using a high-frequency furnace. The compounds were investigated by X-ray diffraction both on powders and single crystals. MgNiGe crystallizes with TiNiSi-type structure, space group Pnma, Z = 4, a = 6.4742(2) Å, b = 4.0716(1) Å, c = 6.9426(2) Å, wR2 = 0.033, 305 F(2) values, 20 variable parameters. SrNiGe and BaNiGe are isotypic and crystallize with anti-SnFCl-type structure (Z = 4, Pnma) with a = 5.727(1) Å, b = 4.174(1) Å, c = 11.400(3) Å, wR2 = 0.078, 354 F(2) values, 20 variable parameters for SrNiGe, and a = 5.969(4) Å, b = 4.195(1) Å, c = 11.993(5) Å, wR2 = 0.048, 393 F(2) values, 20 variable parameters for BaNiGe. The increase of the cation size leads to a reduction of the dimensionality of the [NiGe] polyanions. In the MgNiGe structure the nickel and germanium atoms build a ∞(3)[NiGe] network with magnesium atoms in the channels. In SrNiGe and BaNiGe the ∞(1)[NiGe] ribbons are separated by strontium/barium atoms, whereas in the known CaNiGe structure the ribbons are fused to two-dimmensional atom slabs. The crystal chemistry and chemical bonding in AeNiGe (Ae = Mg, Ca, Sr, Ba) are discussed. The experimental results are reconciled with electronic structure calculations performed using the tight-binding linear muffin-tin orbital (TB-LMTO-ASA) method.

Fully and partially Li-stuffed diamond polytypes with Ag-Ge structures: Li2AgGe and Li2.53AgGe2.

In view of the search for and understanding of new materials for energy storage, the Li-Ag-Ge phase diagram has been investigated. High-temperature syntheses of Li with reguli of premelted Ag and Ge led to the two new compounds Li(2)AgGe and Li(2.80-x)AgGe(2) (x = 0.27). The compounds were characterized by single-crystal X-ray diffraction. Both compounds show diamond-polytype-like polyanionic substructures with tetrahedrally coordinated Ag and Ge atoms. The Li ions are located in the channels provided by the network. The compound Li(2)AgGe crystallizes in the space group R3̅m (No. 166) with lattice parameters of a = 4.4424(6) Å and c = 42.7104(6) Å. All atomic positions are fully occupied and ordered. Li(2.80-x)AgGe(2) crystallizes in the space group I4(1)/a (No. 88) with lattice parameters of a = 9.7606(2) Å and c = 18.4399(8) Å. The Ge substructure consists of unique (1)(∞)[Ge(10)] chains that are interconnected by Ag atoms to build a three-dimensional network. In the channels of this diamond-like network, not all of the possible positions are occupied by Li ions. Li atoms in the neighborhood of the vacancies show considerably enlarged displacement vectors. The occurrence of the vacancy is traced back to short Li-Li distances in the case of the occupation of the vacancy with Li. Both compounds are not electron-precise Zintl phases. The density of states, band structure, and crystal orbital Hamilton population analyses of Li(2.80-x)AgGe(2 )reveal metallic properties, whereas a full occupation of all Li sites leads to an electron-precise Zintl compound within a rigid-band model. Li(2)AgGe reveals metallic character in the ab plane and is a semiconductor with a small band gap along the c direction.

`Pd20Sn13' revisited: crystal structure of Pd6.69Sn4.31

The crystal structure of the title compound, previously reported as ‘Pd20Sn13’ on basis of powder X-ray data, was redetermined on basis of single-crystal X-ray data, resulting in a model with higher precision and accuracy.

TbNb6Sn6: the first ternary compound from the rare earth–niobium–tin system

The title compound, terbium hexaniobium hexastannide, TbNb6Sn6, is the first ternary compound from the rare earth–niobium–tin system. It has the HfFe6Ge6 structure type, which can be analysed as an intergrowth of the Zr4Al3 and CaCu5 structures. All the atoms lie on special positions; their coordination geometries and site symmetries are: Tb (dodecahedron) 6/mmm; Nb (distorted icosahedron) 2mm; Sn (Frank–Caspar polyhedron, CN = 14–15) 6mm and m2; Sn (distorted icosahedron) m2. The structure contains a graphite-type Sn network, Kagome nets of Nb atoms, and Tb atoms alternating with Sn2 dumbbells in the channels.