The crystal structure of the novel ternary silicide Sm4Pd4Si3

The crystal structure of the compound Sm₄Pd₄Si₃ was determined by the single-crystal method (KM-4 automatic diffractometer, Mo K radiation. Sm₄Pd₄Si₄ has the monoclinic Nd₄Rh₄Ge, type structure: space C2/c, mC44 (No. 15). a = 20.693(6), B = 5.584(1), C = 7.699(2) Å, β = 109.48(3)°, V = 838 Å, Z = 4, μ - 36.23 mm¹, R =_F = 0.0537, R _F = 0.0435 for 1652 unique reflections. The coordination numbers of samarium atoms are 17 and 18. For palladium and silicon atoms icosahedra and trigonal prisms with additional atoms are typical as coordination polyhedra. The structure of Sm₄Pd₄Si₄ is composed of fragments of the YPd₂Si and Y₁Rh₂Si₂ structure in a ratio 1:1.     

The ternary thorium aluminium carbides Th2Al2C3 and ThAl4C4

The title compounds were prepared by are-melting cold-pressed pellets of the elemental components with subsequent annealing at 900°C. Th₂Al₂C₃ crystallizes orthorhombic: Pnnm, a = 540.6(1) pm, B = 1155.6(2) pm, C =3 52.01(6) pm, Z = 2. The structure was determined from powder diffractometer data using the Rietveld method: R_F = 0.039 for 42 structure factors and six variable positional parameters. The positions of the metal atoms correspond to those of the InS-type structure. The two different carbon atoms are in octahedral coordination formed by four thorium and two aluminium atoms. The hydrolysis of ThAl₄C₄ with diluted hydrochloric acid resulted in 74 wt.% methane, 12 wt.% ethane and ethylene and 14 wt.% saturated and unsaturated higher hydrocarbons. Nevertheless, the crystal structure determination from single-crystal X-ray data showed that there are only isolated carbon atoms in the solid: I4/m, a = 823.1(1) pm, C = 332.72(6) pm, Z = 2, R = 0.032 for 13 variable parameters and 372 structure factors. It is isotypic with UCr₄C₄. The carbon atoms are octahedrally coordinated by two thorium and four aluminium atoms.     

Preparation and crystal structure of a new barium silicon nitride, Ba5Si2N6

Single crystals of a new ternary nitride, Ba₅Si₂N₆, were synthesized by slow cooling from 750°C using a starting mixture of Ba, Si, Na and NaN₃, where Na and NaN₃ were a flux and a nitrogen source respectively. It crystallizes with orthorhombic symmetry: space group P2₁2₁2₁ (No. 19), A = 6.159, B = 10.305, C = 15.292 Å, and Z = 4. The crystal structure was determined from single-crystal data and refined to R1 = 0.0495 for all 1637 observed reflections and 89 variables. A pair of SiN₄ tetrahedra contained in the structure forms a nitridometallate anion of [Si₂N₆]¹⁰ by edge sharing.     

Ce2Ir5B2, a new structure type of ternary borides

The crystal structure of a new ternary boride Ce₂Ir₅B₂, space group , a=5.477(2) Å, c=31.518(5) Å, Z=6, V=818.79 Å, was refined down to R=0.0484, wR₂=0.1211 from single crystal X-ray diffraction data. This is the first representative of a new structure type of intermetallic compounds (an ordered variant of the binary Er₂Co₇ compound). The structure of Ce₂Ir₅B₂ is the stacking variant of the MgCu₂- and CeCo₃B₂-type slabs and belongs to the structural series with the general formula R_2+nM_4+3nX_2n (n=2).     

Structural investigation of ternary RIr3B2 compounds (R=Ce and Pr)

Structural studies were performed for the ternary RIr₃B₂ compounds (R=Ce and Pr) from as cast samples. The crystal structure of the ternary boride CeIr₃B₂ (CeCo₃B₂ structure type, space group P6/mmm, a=5.520(3) Å, c=3.066(2) Å, Z=1, V=80.91 ų, ρ_x=15.154 g cm⁻³) was refined to R₁=0.0470, wR₂=0.1240 from single-crystal X-ray diffraction data. The new ternary boride PrIr₃B₂ was found to be isostructural with the CeIr₃B₂ compound. Its lattice parameters a=5.5105(2) Å, c=3.1031(1) Å were obtained from a Rietveld refinement of X-ray powder diffraction data.     

Crystal structures and structural relationships of KFe2(SeO2OH)(SeO3)3 and SrCo2(SeO2OH)2(SeO3)2

The new phases KFe₂(SeO₂OH)(SeO₃)₃ and SrCo₂(SeO₂OH)₂(SeO₃)₂ have been synthesized under low-hydrothermal conditions and their structures were determined by single-crystal X-ray methods. Both compounds are monoclinic; KFe₂(SeO₂OH)(SeO₃)₃: space group P2, A = 9.983(4), B = 5.270(1), C = 10.614(4) Å, β = 97.42(2)°, V = 553.7 ų, Z = 2; SrCo₂(SeO₂OH)₂(SeO₃)₂: space group P2ln, A = 14.984(2), B = 5.286(1), C = 13.790(2) Å, β = 94.72(1)°, V = 1088.5 ų , Z = 4. The refinements converged to R-values of 2.9 and 3.6% respectively.

The atomic arrangement in KFe₂(SeO₂OH)(SeO₃)₃ and SrCo₂(SeO₂OH)₂(SeO₃)₂ is based on isolated MO₆ octahedra (M = Fe³⁺, Co²⁺), which are corner-linked via trigonal pyramidal selenite groups to a framework structure. Interstitials are occupied by potassium or strontium atoms in ten- or eight-coordination respectively, and by the lone-pair electrons of the Se⁴⁺ atoms. Both compounds are not isotypic but are closely related and may be interpreted as different distortions of an idealized structure type in space group P2/m, which was modelled for a theoretical compound SrFe₂(SeO₃)₄ by distance least squares refinement (program ).     

Crystal structure and magnetism of the Y2Pd14B5 compound

The crystal structure of the ternary boride Y₂Pd₁₄B₅, space group I4₁/amd, a=8.484(2) Å, c=16.490(3) Å, V=1186.98 ų, Z=4, was refined down to R=0.0475, wR2=0.1276 from single crystal X-ray diffraction data. Two types of coordination for boron atoms were observed: the coordination sphere for the B1 atom is a trigonal prism with one additional atom; the B2 atom has only four neighboring atoms which form a square. No boron–boron contact was observed. Analysis of the Y₂Pd₁₄B₅ crystal structure shows the existence of a correlation between this structure and the Sc₄Ni₂₉B₁₀ structure type. Magnetization and AC susceptibility measurements indicate that there is no superconducting or magnetic transition in Y₂Pd₁₄B₅ down to 2 K.     

Synthesis and structure of a potassium nitridoditungstenate (K6W2N4O3), a potassium digermanate (K6Ge2O7) and a rubidium digermanate (Rb6Ge2O7)

Light yellow single crystals of potassium nitridoditungstate (K₆W₂N₄O₃) and pale single crystals of potassium digermanate (K₆Ge₂O₇) were obtained by the reaction of the metal oxides WO₃ (molar ratio, 1 : 15.7) or GeO₂ (molar ratio, 1 : 2) in alkali metal amide melts in an autoclave at 530–600 °C for 6–8 days. Colourless single crystals of rubidium digermanate (Rb₆Ge₂O₇) were prepared by the reaction of GeO₂ with rubidium amide (molar ratio, 1 : 2) in ammonia at 350 °C in a high-pressure autoclave (H. Jacobs and D. Schmidt, in E. Kaldis (ed.), High-pressure Ammonolysis in Solid State Chemistry, Current Topics in Materials Science, Vol. 8, North Holland, Amsterdam, 1981, p. 379) (p(NH₃) = 5.5 kbar) for 10 days. In all three cases other nitrogen-containing products were present.

The structures of the title compounds were determined on the basis of single-crystal data. They are isotypic or structurally closely related to each other: K₆W₂N₄O₃: P2₁/n, a = 6.720(2) Å, b = 9.473(1) Å, c = 9.581(2) Å, β = 91.99(2)°, Z = 2, R/R_w = 0.040/0.048, N(I) > 3σ(I) 2057, N(Var.) = 71. K₆Ge₂O₇: Pn, a = 6.529(2) Å, b = 9.079(4) Å, c = 9.162(6)Å, β = 91.85(4)°, Z = 2, R/R_w = 0.022/0.024, N(I) 3σ(I) = 1486, N(Var.) = 135. Rb₆Ge₂O₇: P2₁/n, a = 6.839(4) Å, b = 9.437(6) Å, c = 9.460(6) Å, β = 91.53(5)°, Z = 2, R/R_w = 0.061/0.074, N(I) 3σ(I) = 1055, N(Var.) = 71.     

Single crystal preparation and crystal structure of the Cu2Zn/Cd,Hg/SnSe4 compounds

Single crystals of Cu₂Zn/Cd/SnSe₄ were grown using a solution-fusion method. The crystal structure of the Cu₂Zn/Cd,Hg/SnSe₄ compounds were investigated using X-ray powder diffraction. These compounds crystallize in the stannite structure (space group I 2m) with the lattice parameters: a=0.56882(9), c=1.13378(9) nm, c/a=1.993 (Cu₂ZnSnSe₄), a=0.58337(2), c=1.14039(4) nm, c/a=1.955 (Cu₂CdSnSe₄) and a=0.58288(1), c=1.14179(2) nm, c/a=1.959 (Cu₂HgSnSe₄). Atomic parameters were refined in the isotropic approximation (R_I=0.0517, R_I=0.0511 and R_I=0.0695 for Cu₂ZnSnSe₄, Cu₂CdSnSe₄ and Cu₂HgSnSe₄, respectively).     

X-ray investigations of ternary R3Pd4Ge4 samples

Ternary R₃Pd₄Ge₄ samples (R=Nd, Eu, Er) were investigated by means of X-ray single crystal (four circle diffractometer Philips PW1100, MoK radiation) and powder diffraction (MX Labo diffractometer, CuK radiation). The Er₃Pd_3.68(1)Ge₄ compound belongs to the Gd₃Cu₄Ge₄ structure type, space group Immm, a=4.220(2) Å, b=6.843(2) Å, c=14.078(3) Å, R₁=0.0484 for 598 reflections with F_o>4σ(F_o) from X-ray single crystal diffraction data. No ternary R₃Pd₄Ge₄ compound when R is Nd or Eu was observed. The Nd and Eu containing samples appeared to be multiphase. Ternary phases observed in the Nd₃Pd₄Ge₄ and Eu₃Pd₄Ge₄ alloys and their crystallographic characteristics are the following: NdPd₂Ge₂, CeGa₂Al₂ structure type, space group I4/mmm, a=4.3010(2) Å, c=10.0633(2) Å (X-ray powder diffraction data); NdPd_0.6Ge_1.4, AlB₂ structure type, space group P6/mmm, a=4.2305(2) Å, c=4.1723(2) Å (X-ray powder diffraction data); Nd(Pd_0.464(1)Ge_0.536(1))₂, KHg₂ structure type, space group Imma, a=4.469(2) Å, b=7.214(2) Å, c=7.651(3) Å, R₁=0.0402 for 189 reflections with F_o>4σ(F_o) (X-ray single crystal diffraction data); Eu(Pd,Ge)₂, AlB₂ structure type, space group P6/mmm, a=4.311(2) Å, c=4.235(2) Å; EuPdGe, EuNiGe structure type, space group P2₁/c, and ternary compound with unknown structure (X-ray powder diffraction data).     

Determination of the structure of UFe2Al10 compound

The atomic structure of a new ternary phase UFe₂Al₁₀ appearing in the U–Fe–Al system was determined using direct methods applied to X-ray powder diffraction data. High resolution electron microscopy combined with the methods of crystallographic image processing was used for the verification of the structural model. The UFe₂Al₁₀ phase is orthorhombic and belongs to Cmcm space group, its unit cell contains 40 Al, eight Fe, and four U atoms. The lattice parameters obtained after Rietveld refinement are: a=8.919 Å, b=10.208 Å, and c=9.018 Å. The reliability factors characterizing the Rietveld refinement procedure are: R_p=5.9%, R_wp=8.1%, and R_b=2.9%.     

Structural chemistry and magnetism of dicyclopentadienidehalides of lanthanides Part 8: terbiumdicyclopentadienidebromide [Tb(C5H5)2Br]2

A single-crystal X-ray structural investigation of [Tb(C₅H₅)₂Br]₂ revealed the [Sc(C₅H₅)₂Cl]₂-type structure, space group P2₁/c, with a = 1407.6(2) pm, b = 1644.7(2) pm, c = 1370.6(9) pm, β = 93.46(3)°, V = 3167(2) × 10⁶ pm³, D_c = 2.322 g cm⁻³ and Z = 6 dimers (R = 0.036 for 4627 reflections with I > 3σ(I)). The metal centres have the pseudosymmetry C_2v. Magnetic susceptibility data show Curie-Weiss behaviour between 213 and 6 K with θ_p = −4.5(3) K and a magnetic moment μ = 9.8(1) μ_B close to the Tb³⁺ free-ion value (9.72 μ_B). Below 6 K, deviations from Curie-Weiss behaviour are observed, and at 5.3 K a maximum in the susceptibility is detected which may be caused by intradimer antiferromagnetic spin coupling. The magnetic properties are compared with the prediction of various models, starting from cubic crystal fields and isotropic intramolecular exchange interactions, followed by extension to lower crystal field symmetry (orthorhombic) and anisotropic contributions to the spin coupling. However, a reasonable agreement between the measured and calculated data was not obtained. As in [Gd(C₅H₅)₂Br]₂, the low-temperature behaviour is governed by effects which cannot be described by spin coupling models in the generally accepted form.     

Mg6Ir2H11, a new metal hydride containing saddle-like [IrH4] and square-pyramidal [IrH5] hydrido complexes

Mg₆Ir₂H₁₁ has been synthesised by both hydrogenation of the intermetallic compound Mg₃Ir at 20 bar and 300 °C, and sintering of the elements at 500 °C under 50 bar hydrogen pressure. Neutron powder diffraction on the deuteride indicates a monoclinic structure (space group P2₁/c, Mg₆Ir₂D₁₁: a=10.226(1), b=19.234(2), c=8.3345(9) Å, β=91.00(1)°, T=20 °C) that is closely related to orthorhombic Mg₆Co₂H₁₁. It contains a square-pyramidal [IrH₅]⁴⁻ complex and three saddle-like [IrH₄]⁵⁻ complexes of which one is ordered and two are disordered. Five hydride anions H⁻ are exclusively bonded to magnesium. The compound has a red colour, is presumably non-metallic and decomposes under 3 bar argon at 500 °C into Mg₃Ir, iridium and a previously unreported intermetallic compound of composition Mg₅Ir₂.     

Crystal structures of the Ag4HgGe2S7 and Ag4CdGe2S7 compounds

The crystal structures of the Ag₄HgGe₂S₇ and Ag₄CdGe₂S₇ compounds were investigated using X-ray powder diffraction. These compounds crystallize in the monoclinic Cc space group with the lattice parameters a=1.74546(8), b=0.68093(2), c=1.05342(3) nm, β=93.398(3)° for Ag₄HgGe₂S₇ and a=1.74364(8), b=0.68334(3), c=1.05350(4) nm, β=93.589(3)° for Ag₄CdGe₂S₇. Atomic parameters were refined in the isotropic approximation (R_I=0.0761 and R_I=0.0727, respectively).     

Praseodymium diiodide, PrI2, revisited by synthesis, structure determination and theory

Praseodymium diiodide, PrI₂, is obtained from the triiodide, PrI₃, by reduction with praseodymium metal at elevated temperatures. The two modifications, PrI₂-IV and -V, are obtained in different ratios upon fast and slow cooling, respectively. PrI₂-IV crystallizes with the CdCl₂ type of structure (trigonal, R-3m, a=426.5(1), c=2247.1(8) pm) while PrI₂-V (cubic, F-43m, a=1239.9(2) pm) represents an own structure type that may be considered as a structural variant of the CdCl₂ type with tetrahedral Pr₄ clusters. To elucidate the electronic properties of the modifications of PrI₂ first principles electronic band structure calculations have been carried out using the tight-binding linear-muffin-tin-orbital method (LMTO) as well as the full potential augmented plane wave method (FP-LAPW). The band structure and the bonding were analysed in terms of projections of the bands onto orthogonal orbitals. It was especially focussed on Pr–Pr interactions by crystal orbital Hamiltonian population (COHP) analysis. The calculations show accordingly that a configurational crossover between a [Xe]6s⁰5d⁰4fⁿ and a [Xe]6s⁰5d¹4f^n-1 configuration can be observed in the case of PrI₂, depending upon the structure adopted. A higher d orbital contribution results in stronger Pr–Pr interactions. Thus, the driving force appears to be an optimisation of bonding.     

Ba3YB3O9: phase transition and crystal structure

A new modification of the compound Ba₃YB₃O₉, β phase, has been attained through solid phase transition from phase at 1125–1134 °C. β-Ba₃YB₃O₉ crystallizes in the hexagonal space group with cell parameters a=13.0529(8) Å, c=9.5359(9) Å. The crystal structure of -Ba₃YB₃O₉ has been determined from powder X-ray diffraction (XRD) data. The refinement was carried out using the Rietveld methods and the final refinement converged with R_p=8.8%, and R_wp=11.8% with R_exp=5.65%. In its structure, the isolated [BO₃]³⁻ anionic groups are parallel to each other and distributed layer upon layer along the c-axis. The Y atoms are six-coordinated by the O atoms to form octahedra. The result of IR spectrum confirmed the existence of [BO₃]³⁻ triangular groups.     

Crystal structure of Zr9Co7In14

Zr₉Co₇In₁₄ crystallizes in the cubic system, space group Fm3m, a = 13.300(2) Å Z = 2, R = 0.0412 for 567 unique reflection (KM-4 diffractometer, Mo K radiation). The crystal structure, related to the Cr₂₄C₆ -type structure, can be described as a stacking of columns of cubes, tetragonal antiprisms, and cubo-octahedrons extending along the coordinate axes. One of the ln atoms is coordinated by a Frank-Kasper polyhedron.     

Magnetic behaviour of two AlB2-related germanides: CePd0.63Ge1.37 and CeAu0.75Ge1.25

The title compounds were prepared from the elemental components by arc-melting and subsequent annealing at 1020 K and 1170 K. Both CePd_0.63Ge_1.37 and CeAu_0.75Ge_1.25 crystallize in the AlB₂ structure type with a statistical distribution of the transition metal and germanium atoms on the boron site. The structure of CeAu_0.75Ge_1.25 was refined from single crystal X-ray data: P6/mmm, a=433.5(1) pm, c=422.6(1) pm, V=0.0688(1) nm³, Z=1, wR2=0.0504 for 157 F² values and 7 variables. Magnetic susceptibility data for both compounds show a full cerium moment and ferromagnetic ordering at 6.0(5) K for CeAu_0.75Ge_1.25 and 3.0(5) K for CePd_0.63Ge_1.37. The crystal structure and properties of CeAu_0.75Ge_1.25 are compared with those of equiatomic CeAuGe which adopts the NdPtSb structure type, an ordered variant of AlB₂.     

Ce(Au,Sb)2 with UHg2 structure type, a new member of the AlB2 family

A new ternary compound Ce(Au,Sb)₂, with a homogeneity range has been observed from X-ray powder diffraction of as cast alloys, a = 4.743–4.712 Å, c = 3.567–3.768 Å. Its crystal structure was investigated by X-ray diffraction from Ce(Au_1−xSb_x)₂ (x = 0.266) single crystal: CAD-4 automatic diffractometer, Mo K radiation, a = 4.7256(6) Å, c = 3.6711(6) Å, P6/mmm space group, V = 70.997(17) Å³, Z = 1, ρ = 10.732 Mg/m³, μ = 76.369 mm⁻¹, R₁ = 0.0415, wR₂ = 0.0793 for 99 reflections with I > 2σ(I₀). The coordination polyhedron of X (X = 0.734Au + 0.266Sb) atom is a full-capped trigonal prism [XCe₆X₃X₂]. Ce atom is coordinated by 14 atoms: [CeX₁₂Ce₂]. The compound is isotypic with UHg₂ structure, a deformation derivative of AlB₂ structure type. It forms isostructural compounds with La and Pr.     

Synthesis and structure of TlCuTiTe3

The new compound TlCuTiTe₃ has been synthesized from Tl₆Te₄ and the corresponding elements and characterized by single-crystal X-ray diffraction methods. TlCuTiTe₃ crystallizes in the space group C_2b²−P2₁/m of the monoclinic system with two formula units in a cell of dimensions a = 8.409(8) Å, B = 3.956(3) Å, C = 10.261(8) Å, β = 111.56(4)°, V = 317.5(4) ų (T = 115 K). The two-dimensional structure comprises slabs of alternating pairs of Ti octahedra and Cu tetrahedra. The slabs are separated by Tl′ cations coordinated to Te³ anions in a monocapped trigonal prismatic fashion. Whereas the structure of the individual slabs in TlCuTiTe₄, is strikingly similar to those found in the related materials NaCuTiS₃, NaCuZrSe₃, and NaCuZrTe₃, the packing of the slabs is different. Two-probe resistivity measurements indicate that TlCuTiTe₃ is a semiconductor.