Neue AB2X2-Verbindungen mit CaBe2Ge2-Struktur

New AB₂X₂ Compounds with CaBe₂Ge₂ Structure Crystal structure of ternary RELi₂Sb₂ compounds (RE = Ce, Pr, Nd) is reported. The compounds are isotypic and crystallize tetragonally in the CaBe₂Ge₂ structure (space group P4/nmm), which is a modified type of the ThCr₂Si₂ structure.     

Ternäre Palladiumpnictide der Erdalkali- und Seltenen Erdmetalle mit ThCr2Si2- und CaBe2Ge2-Struktur

Fifteen compounds of compositionMPd₂ Pn ₂ (M = alkaline earth or rare earth metal,Pn = As, Sb, Bi) were prepared. TheirGuinier powder patterns show that the arsenides crystallize with the ThCr₂Si₂ type structure, the bismuthides with the closely related CaBe₂Ge₂ type structure. The antimonides most likely also have the CaBe₂Ge₂ structure as is demonstrated by a structure refinement of EuPd₂Sb₂ from single crystal X ray data (R = 0.039 for 366 independent structure factors and 15 variable parameters). The structure of SrPd₂As₂ (ThCr₂Si₂ type) was refined to a residual ofR = 0.020 for 182F values and 9 variables. EuPd₂Sb₂ is paramagnetic and a metallic conductor. A comparison of the cell volumes suggests intermediate valency for Eu in EuPd₂As₂.Chemical bonding and especially the reasons for the adoption of the ThCr₂Si₂ or CaBe₂Ge₂ type structures by these compounds are discussed. It is suggested that in going from the phosphides to the bismuthides the ThCr₂Si₂ structure is loosing and the CaBe₂Ge₂ structure is gaining stability due to decreasing Pd-Pd bonding and increasing Pd-pnictogen bonding. This trend is caused by the increasing size of the pnictogen component.

     

Synthesis and crystal structures of the manganous antimonates Mn2Sb2O7 and MnSb2O6

Mn₂Sb₂O₇ has been prepared by the solid state reaction of MnCO₃ and Sb₂O₃ at 1100°C, and its crystal structure determined from X-ray powder diffraction data. The compound is trigonal P3₁21 with a = 7.191, c = 17.398 Å, and the structure is fluorite-related, but not a distorted pyrochlore. The relationship between this structure and that of pyrochlore is discussed. MnSb₂O₆ was formed as a reaction intermediate and its structure has also been determined. This phase is trigonal P321 with a structure related to that of Na₂SiF₆ and is apparently a new polymorph, since MnSb₂O₆ has previously been stated to have either the orthorhombic columbite or the tetragonal trirutile structure.     

Tb2Ni2Mg3: a new structure type derived from the Ru3Al2B2 type

Single crystals of diterbium dinickel trimagnesium, Tb₂Ni₂Mg₃, were synthesized from the elements by induction melting. The novel compound crystallizes in the space group Cmmm with one Mg atom of site symmetry mmm and the Tb, Ni and other Mg atom in m2m positions. This ternary compound represents a new structure type that is derived from Ru₃Al₂B₂ by way of Wyckoff site distribution. The two‐layer structure of Tb₂Ni₂Mg₃ is a new representative of a homologous linear structure series of general formula R′_k+nX_2nR′′_2m+k based on structural fragments of the α‐Fe, CsCl and AlB₂ structure types. The Tb atoms in the structure are enclosed in 17‐vertex polyhedra, while rhombododeca­hedra and distorted rhombododeca­hedra surround the Mg atoms, and equatorially tricapped trigonal prisms form around the Ni atoms. All inter­atomic distances indicate metallic type bonding.     

Die Kristallstruktur von VO2JO3·2H 2O

The Crystal Structure of VO₂IO₃·2 H₂O VO₂IO₃ possesses a layer structure and crystallizes in the space group P2₁/c with a = 9.848(3) Å, b = 8.l58(2) Å, c = 7.192(2) Å, β = 102.17(2)° and four formula units in the unit cell. The individual layers of the structure consist of highly distorted corner- and edgesharing IO₆, and VO₆, octahedra. Only one oxygen atom is bound terminally at the vanadium, as is shown by the vibrational spectrum, too.     

The effects of La2O3 on the early stages of crystallization for MgO-Al2O3-SiO2-TiO2-La2O3 glass-ceramics

The early stages of crystallization for MgO-Al₂O₃-SiO₂-TiO₂-La₂O₃ glasses with different La₂O₃ concentrations were studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The glass transition temperature (Tg) of the glass decreases at first and then increases again with increasing La₂O₃ concentration. This indicates that the structure of the glass becomes weaker at first and then stronger again. Lanthanum acts in glasses as network modifier and will usually decrease the network connectivity of the glass structure. Nevertheless, if the La₂O₃ concentration is high enough, the oxygen and other ions start to agglomerate around La, resulting in a more closely packed structure. Heat-treatment of the sample with x = 0.1 at 770–810 °C results in the precipitation of a droplet phase with higher mean atomic weight embedded in a matrix with lower mean atomic weight. The initial crystalline phase magnesium aluminum titanate (MAT) precipitates from the droplet phase. Nevertheless, for the sample with x = 0.4, dendrite-like structure could be observed after heat-treatment of the glass at 810 °C. Furthermore, the crystalline phase first precipitated is the lanthanum containing perrierite, which could be attributed to the rearrangement of the glass structure as an effect of La³⁺ incorporation.     

New complex borides with ReB2- and Mo2IrB2-type structure

The compound V_0.4Os_0.6B₂ was found to crystallize with ReB₂-type structure. V₂OsB₂, Mo₂OsB₂, and W₂OsB₂ are isotypic with the crystal structure of Mo₂IrB₂. The crystal chemistry of complex borides with ReB₂- and Mo₂IrB₂-type structure is discussed.     

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.     

Synthesis,structure and properties of Ag2PdO2

The first silver palladium oxide, Ag₂PdO₂, was synthesised from a co-precipitated oxide precursor by annealing at 423–823 K, applying an oxygen pressure of 73 MPa. The crystal structure has been determined from X-ray and neutron powder diffraction data. The new compound crystallises in space group Immm. The lattice constants as determined from X-ray powder diffraction are a=4.55523(5) Å, b=3.00803(3) Å and c=9.8977(1) Å. The crystal structure constitutes a new structure type showing some features in common with the Li₂CuO₂-type. Palladium is found in a nearly square planar arrangement while silver has an almost linear co-ordination. The overall structure can be considered as a rocksalt defect structure. Ag₂PdO₂ is diamagnetic and semiconducting. The band gap, estimated from conductivity measurements in the temperature range of 240–300 K, is 0.18(2) eV.     

Synthesis and Characterization of Copper Hexathiometadiphosphate Cu2P2S6

Copper hexathiometadiphosphate, Cu₂P₂S₆, was synthesized and characterized. Brick‐red copper hexathiometadiphosphate Cu₂P₂S₆ crystallizes in the tetragonal space group P4₂/mnm (no. 136) with a = b = 5.2565(7), c = 15.066(3) Å and V = 416.3(1) ų in a novel structure type. This is the first hexathiometadiphosphate, whose crystal structure is based on a slightly distorted cubic closest packing of sulfur atoms. 1/3 of the tetrahedral voids are occupied by Cu and P in an ordered fashion, thus resulting in a layered structure. The structural motif of layers composed of corner‐sharing CuS₄ tetrahedra (comparable to red HgI₂) that are separated by [P₂S₆]^2– anions orientated perpendicular to these layers, is rarely found in solid state chemistry. The compound is diamagnetic and shows negligible electronic conductivity. Electronic structure calculations and UV/Vis measurements point to a bandgap in the visible range and explain the red color of the compound. Additionally, the oxidation state +1 for Cu was confirmed by the electronic structure calculations. The thermal properties of Cu₂P₂S₆ were investigated by DTA.     

Zur Kenntnis der Dialkalimetalldichalkogenide β-Na2S2, K2S2, α-Rb2S2, β-Rb2S2, K2Se2, Rb2Se2, α-K2Te2, β-K2Te2 und Rb2Te2

On Dialkali Metal Dichalcogenides β-Na₂S₂, K₂S₂, α-Rb₂S₂, β-Rb₂S₂, K₂Se₂, Rb₂Se₂, α-K₂Te₂, β-K₂Te₂ and Rb₂Te₂ The first presentation of pure samples of α- and β-Rb₂S₂, α- and β-K₂Te₂, and Rb₂Te₂ is described. Using single crystals of K₂S₂ and K₂Se₂, received by ammonothermal synthesis, the structure of the Na₂O₂ type and by using single crystals of β-Na₂S₂ and β-K₂Te₂ the Li₂O₂ type structure will be refined. By combined investigations with temperature-dependent Guinier-, neutron diffraction-, thermal analysis, and Raman-spectroscopy the nature of the monotropic phase transition from the Na₂O₂ type to the Li₂O₂ type will be explained by means of the examples α-/β-Na₂S₂ and α-/β-K₂Te₂. A further case of dimorphic condition as well as the monotropic phase transition of α- and β-Rb₂S₂ is presented. The existing areas of the structure fields of the dialkali metal dichalcogenides are limited by the model of the polar covalence.     

Kristallstruktur von LiHC2O4-H2O

LiHC₂O₄ · H₂O crystallizes in space group P 1 with a₀ = 4.99, b₀ = 6.16, c₀ = 3.45 Å; α₀ = 96.3°, β₀ = 98.0°, γ₀ = 80.4° and Z = 1. The crystal structure has been determined by direct methods. Refinement by least squares methods resulted to R₁ = 8,3%. In the structure the oxalate group is not planar. The angle between the two O? C? O planes is 2.9°.     

Zur Kristallstruktur von Rb2C2 und Cs2C2

On the Crystal Structure of Rb₂C₂ and Cs₂C₂ By reaction of rubidium or caesium solved in liquid ammonia with acetylene AC₂H with A = Rb, Cs was obtained, which was subsequently converted into the binary acetylide A₂C₂ in vacuum at temperatures of 520 K (Rb₂C₂) and 470 K (Cs₂C₂) using a surplus of the respective alkali metal. The crystal structures of the very air sensitive compounds were solved and refined by a combination of both neutron and X‐ray powder diffraction data. Rb₂C₂ as well as Cs₂C₂ coexist in two modifications. The hexagonal modification (P 6 2m, Z = 3) crystallises in the known Na₂O₂ structure type with two crystallographic independent sites for the C₂^2– dumbbells. For the orthorhombic modification (Pnma, Z = 4) a new structure type was found, which is related to the PbCl₂ structure type with ordered C₂^2– dumbbells occupying the Pb sites. Temperature dependent investigations between 4 K and the decomposition temperature by the means of neutron and X‐ray powder diffraction resulted in a very complex dynamic disorder of the C₂ dumbbells, which is still not completely understood. The frequencies of the C–C stretching vibration determined by the help of Raman spectroscopy fit nicely to the results obtained for other alkali metal acetylides and alkali metal hydrogen acetylides. These results seem to indicate that the electronegativity of the alkali metal has a strong influence on the frequency of the C–C stretching vibration.     

Commensurate monoclinic form of Ca2Zn0.97Co0.03Ge2O7

Cobalt‐doped dicalcium zinc germanate, synthesized by slow cooling from the melt, is monoclinic and has a layered structure, which is different from the modulated melilite‐type structure of Ca₂ZnGe₂O₇. The monoclinic form has two different Ca, one Zn and two Ge sites, and seven independent O‐atom positions; all are in general position 4e of the space group P2₁/n. The topology of the structure is described and compared with that of Ca₂ZnGe_1.25Si_0.75O₇.     

Synthesis and crystal structure of two new Bi(III) complexes {(Me2NCS2)3Bi}2 and {[(CH2)5NCS2]2BiI}2

Six bismuth(III) complexes containing dithio-ligands formulated as (R₂NCS₂)₃Bi [R₂NCS₂M?=?Me₂NCS₂Na, C₄H₈NCS₂Na, Bz₂NCS₂Na] and [(R₂NCS₂)₂BiI]₂ [R₂NCS₂M?= C₅H₁₀NCS₂Na, ⁿ Bu₂NCS₂Na, OC₄H₈NCS₂Na] have been obtained by reactions of bismuth(III) halides with dithiocarbamate ligands in 1?:?2 or 1?:?3 stoichiometry. All compounds were characterized by elemental and IR analyses. The crystal structures of complexes 1 and 4 have been determined by X-ray single crystal diffraction. The structure analyses reveal that Bi^III in complex 1 adopts a distorted pentagonal–pyramidal coordination, due to its stereochemically active lone pair of electrons. A long Bi?·?S contact of 3.218 (3)?Å leads to dimeric associations of molecules in the crystal structure. The structure of complex 4 is six-coordination with a distorted octahedral configuration. Intramolecular S?·?S weak interactions contribute to the stability and lead to a one-dimensional chain structure.     

Ba2(CN2)(CN)2 und Sr2(CN2)(CN)2 – die ersten gemischten Cyanamid-cyanide

Ba₂(CN₂)(CN)₂ and Sr₂(CN₂)(CN)₂ – the First mixed Cyanamide Cyanides The mixed cyanamide-cyanides M₂(CN₂)(CN)₂ (M = Ba, Sr) were synthesized by the reaction of Ba₂N and SrCO₃, respectively, with HCN at 630°C. The crystal structure of Ba₂(CN₂)(CN)₂ was determined from single-crystal X-ray investigations at room temperature and ?100°C; the isostructural Sr₂(CN₂)(CN)₂ was refined using powder methods (P6₃/mmc; Ba₂(CN₂)(CN)₂: a = 1 066.52(5) pm, c=696.82(3) pm; Sr₂(CN₂)(CN)₂: a = 1 035.91(1) pm, c = 664.23(1) pm; Z = 4). The crystal structure is a partially filled defect variant of the anti-NiAs structure type with a distorted hexagonal close packed arrangement of M²⁺-ions. All CN₂^2? and one quarter of the CN^? ions occupy 3/4 of the octahedrally coordinated interstices, the remaining cyanide anions are located at 3/8 of the tetrahedral sites. In the crystal structure the CN^? are coordinated to the cations both end-on and side-on. All anions can be distinguished by vibrational spectroscopy.     

Crystal structure of a new digermanate: Al2Ge2O7

The structure of Al₂Ge₂O₇ has been determined by using a single crystal. The symmetry is monoclinic ($\text{C2}\text{c}\text{, Z = 4}$) with unit cell parameters a = 7.132(1) Å, b = 7.741(1) Å, c = 9.702(2) Å, β = 110.62(2)°. The structure is characterized by digermanate groups (Ge₂O₇) and by AlO₅ bipyramids with two common edges forming (AlO₃)_∞ chains. The relationship with the thortveitite structure is discussed in terms of coordination polyhedra.     

Synthesis and Structure of ThTe2I2

The new ternary compound ThTe₂I₂, which crystallizes in the NbS₂Cl₂ structure type, was prepared from the elements and characterized by single‐crystal X‐ray diffraction. It adopts a monoclinic layer structure where binuclear [Th₂(Te₂)₂]⁴⁺ units with square‐antiprismatically coordinated thorium are linked together by I^– anions to form sheets parallel to the (001) plane. The space group is C2/m and the lattice constants are a = 7.642(1) Å, b = 14.336(4) Å, c = 7.727(2) Å, and β = 111.27(2)° for Z = 4. The final R1/wR2 for the crystal structure refinement was 0.029/0.073.     

Magnesium chloride tetrahydrate,MgCl2·4H2O

The title compound, MgCl₂·4H₂O, was crystallized at 403 K and its structure determined at 200 K. The structure is built up from MgCl₂(H₂O)₄ octahedra with a trans configuration. Each complex is situated on a crystallographic twofold axis, with the rotation axis aligned along one H₂O—Mg—OH₂ axis. They are connected by a complex network of O—H...Cl hydrogen bonds. The structure contains two‐dimensional sections that are essentially identical to those in the reported tetrahydrates of CrCl₂, FeCl₂, FeBr₂ and CoBr₂, but they are stacked in a different manner in MgCl₂·4H₂O compared with the transition metal structures.     

Penkvilksite‐2O: Na2TiSi4O11·2H2O

The crystal structure of synthetic penkvilksite‐2O, disodium titanium tetrasilicate dihydrate, Na₂TiSi₄O₁₁·2H₂O, a microporous titanosilicate, confirms the major features of a previous model that had been obtained by order–disorder (OD) theory from the known structure of penkvilksite‐1M. An important difference from the previous model involves the hydrogen bonding of the water molecule which, on the basis of a Raman spectrum and the finding of only one of the two H atoms, is proposed to be disordered about a fixed O–H direction. The structure of penkvilksite‐2O is based on (100) silicate layers linked by isolated TiO₆ octahedra to form a heteropolyhedral framework. The layer is strongly corrugated, based on interlaced spiral chains, and is crossed by two different channels that have an effective channel width of about 3 Å.