The crystal structure of α-SrMnO3

α-SrMnO₃ crystallizes in the hexagonal system with unit-cell dimensions a = 5.454(1) Å, c = 9.092(2)Å, space group $\text{P6}{}_3\text{mmc}\text{, Z = 4}$. The structure was solved by the heavy-atom method; of 404 unique reflections measured by counter method, 203 that obeyed the condition |F₀| ≥ 3σ (|F₀|) were used in the refinement to a conventional R value of 0.043. The structure consists of four close-packed SrO₃ layers in an ABAC stacking sequence along the hexagonal c axis. Oxygen octahedra containing Mn⁴⁺ are grouped into face-sharing pairs linked by corner sharing within the cubically stacked “A” layer.     

The crystal structure of β-Ga2Se3

From new X-ray powder diffraction data reported in this paper, the structure of the ordered, superstructural phase of Ga₂Se₃ is found to be different from the structures stated in the literature up to now. The difference relates essentially to the structure distortion involved in the formation of the superstructure. This distortion is clarified in a way which, in general, is suitable for investigations of small distortions of cubic structures. The superstructure cell turns out to be monoclinic, with a = 6.6608(3), b = 11.6516(4), c = 6.6491(3) Å, β = 108.840(5)°, and Z = 4. Furthermore, the coordinates of the Ga and Se positions in this cell are deduced. The space group is shown to be C⁴_s-Cc (No. 9).     

Coordination and bonding in Fe3PTi3PV3STa3As-type compounds: The crystal structures of Hf3Sb and h-Ta3Ge

Interatomic distances in Hf₃Sb and h-Ta₃Ge (Fe₃P-type structure, space group $\text{I}\text{4}\text{, Z = 8}$) have been determined by crystal structure refinements based on Rietveld-type full-profile analyses of Guinier-H:agg X-ray powder film intensity data. The results, together with data from the recently refined Hf₃As and Ta₃As structures, are included in a survey of coordination and bonding in Fe₃PTi₃PV₃STa₃As-type compounds. It is shown that the trends in atomic coordination observed can be explained in terms of an interplay of d-d and d-p electronic interactions.     

Synthesis and structure of ternary transition-metal silicides Zr3Mn4Si6 and Hf3Mn4Si6

The isostructural ternary transition-metal silicides Zr₃Mn₄Si₆ and Hf₃Mn₄Si₆ can be prepared by direct reaction of the elemental components or by arc-melting. The single-crystal structure of Zr₃Mn₄Si₆ was determined by X-ray diffraction (Pearson symbol tP104, tetragonal, space group P4₂/mbc, Z=8, , ). Zr₃Mn₄Si₆ is isostructural to Nb₃Fe₃CrSi₆ and contains an essentially ordered arrangement of the transition-metal atoms. Square antiprismatic clusters with Zr and Mn atoms at the corners and Si atoms at the center share opposite faces to form one-dimensional columns extending along the c direction. These columns occupy channels that are outlined by a framework of edge- and face-sharing MnSi₆ octahedra. The extensive metal-metal interactions in the structure are complemented by Si-Si bonding in the form of dumbbells, linear chains, and zigzag chains.     

The crystal structure and some properties of Eu2Sb3

The Mooser-Pearson phase Eu₂Sb₃ crystallizes in a new monoclinic structure type, space group $\text{P2}{}_1\text{c}$ (No. 14) with a = 6.570(1) Å, b = 12.760(2) Å, c = 15.028(2) Å, β = 90.04(1)°; Z = 8. The Sb atoms form six-membered twisted chain fragments oriented along the b-axis. The Eu atoms are eight- and nine-coordinated by Sb. The Eu₂Sb₃ structure is closely related to the structure of Ca₂As₃. The relations between their space-group symmetries are derived and hypothetical higher-symmetry structures are discussed. The semiconducting Eu₂Sb₃ is antiferromagnetic below T_N = 14.4°K. An Eu₂Sb₃-type structure was found also for Sr₂Sb₃.     

The crystal structure of 3-R Nb1.06S2

The X-ray single crystal structure of 3-R Nb_1.06S₂ has been determined. The material crystallizes in the space group R_3m with a = 3.3285(4) and c = 17.910(4) Å when indexed on a hexagonal lattice. The structure was refined by full matrix least squares procedures to a final residual of R = 0.026 based on 79 observed (I > 3σ_I) reflections. The sulfurs form closest-packed layers with the majority of the metal in sheets of trigonal prismatic sites. A small portion of niobium was found to occupy octahedral sites, between the van der Waals gaps of the sulfur lattice. Niobium in the van der Waals region is trigonally distorted from octahedral symmetry, with niobium-sulfur distances of 2.234(8) and 2.577(11) Å, because of repulsion from niobium in adjacent trigonal prismatic layers.     

The synthesis and crystal structure of α-Ca3UO6

Single crystals of α-Ca₃UO₆ were grown from a UO₃CaCl₂CaO melt by the slow cooling method from 950°C. The crystal structure was determined by means of X-ray diffraction with R = 0.032 and R_w = 0.019. The structure of α-Ca₃UO₆ is of Mg₃TeO₆ type. α-Ca₃UO₆ is rhombohedral with a = 6.729 (1)Å, α = 90.30 (1)°, Z = 2, D_c = 4.955 g/cm³, D_m = 4.79 g/cm³, space group $\text{R}\text{3}$. Uranium and calcium atoms are six-coordinated. At 1200°C rhombohedral α-Ca₃UO₆ irreversibly transforms to monoclinic β-Ca₃UO₆.     

The crystal structure of niobium trisulfide,NbS3

The crystal structure of NbS₃ was determined from single-crystal diffractometer data obtained with MoKα radiation. The compound is triclinic, space group $\text{P}\text{1}$, with: a 4.963(2) Å; b = 6.730(2) Å; c = 9.144(4)Å; α = 90°; β = 97.17(1)°; γ = 90°. The structure is closely related to the ZrSe₃ structure type; it shows that the compound can be formulated as Nb⁴⁺(S₂)^2?S^2?, in agreement with XPS spectra. The main difference with ZrSe₃ is that the Nb atoms are shifted from the mirror planes of the surrounding bicapped trigonal prisms of sulfur atoms to form NbNb pairs (NbNb = 3.04 Å); this causes a doubling of the b axis relative to ZrSe₃ and a decrease of the symmetry to triclinic.     

The crystal structure of Lu3S4: A new population wave structure

The monosulfide of lutetium loses lutetium preferentially upon vaporization in vacuo at 1750°C, and the quenched samples exhibit a new structure which is formed by an ordering of metal vacancies on the rock-salt type lattice.     

The crystal structure of Ca3Cu3(PO4)4

Single crystals of Ca₃Cu₃(PO₄)₄ synthesized hydrothermally at 420°C and 55 kpsi (3.8 kbar) were found to occur in the space group $\text{P2}{}_1\text{a}$ (No. 14) with a = = 17.619(2), b = 4.8995(4), c = 8.917(1)Å, β = 124.08(1)°, and Z = 2. Full-matrix least-squares refinement of the structure using diffractometer data converged to a final anisotropic R = 0.037 (R_w = 0.046). The two calcium atoms are in six- and nine-coordination and the two copper-containing polyhedra (four- and five-coordinated) are similar to those previously found in Cu₃(PO₄)₂.     

The crystal structure of magnesium arsenate,Mg8.5As3O16

Single crystals of magnesium arsenate have been grown from a PbOAs₂O₅ eutectic by flux crystallization of a ceramic preparation having an initial composition of 6MgO·As₂O₅. The crystals are rhombohedral, space group $\text{R}\text{3}\text{m}$, with hexagonal unit cell parameters a = 6.0278(6) and c = 27.600(3) Å. A three-dimensional structural analysis using automatic diffractometer data has been completed and refined by full-matrix least-squares procedures to a residual R = 0.049 (R_w = 0.059) with a data-parameter ratio of 36 in the final anisotropic refinement. The structure analysis indicated that magnesium arsenate has the composition Mg_8.5As₃O₁₆ and is isostructural with the previously reported Co₈As₃O₁₆. The structure is based upon a cubic close-packed oxygen array with charge balance achieved in magnesium arsenate through partial occupancy of a unique magnesium site occurring in an arsenic-substituted MgO-type layer.     

The preparation and crystal structure of a BaRhO3 polytype

Barium rhodium oxide, BaRhO₃, was prepared at 1175°C and 60–65 kbar by the reaction of BaO₂ and RhO₂. A hexagonal black platelet obtained in the reaction product was found to possess a four-layer stacking sequence in space group $\text{P6}{}_3\text{mmc}$ having hexagonal unit cell parameters a = 5.744(1), c = 9.642(1) Å. The structure was detemined from 707 independent reflections of which 224 were considered observed. Averaging equivalent reflections yielded 132 unique observed reflections. Refinement of the structure by least-squares methods gave a conventional R value of 4.4%. The structure consists of a four-layer stacking sequence of close-packed BaO₃ layers containing tetravalent rhodium in all the octahedral oxygen interstices. The compound was found to be isostructural with previously reported BaMO₃ phases. This is the first single-crystal refinement of the 4H polytype using a four-circle diffractometer.     

Crystal structure predictions: the crystal and electronic structure of Zr1−δV1+δAs

Zr_1−δV_1+δAs is accessible via arc-melting of different mixtures of ZrAs, VAs, Zr, and V. It crystallizes in the tetragonal La₂Sb type, with a phase range of −0.43(4)?δ?0.15(1). The lattice dimensions (a=382.4(1) pm, c=1486.8(6) pm for Zr_1.43(4)V_0.57As; and a=375.77(7) pm, c=1400.2(3) pm for Zr_0.85(1)V_1.15As) strongly depend on δ because of the different sizes of the Zr and V atoms. The ZrVAs structure comprises sheets of (empty) M₆ octahedra, whose triangular faces are capped by the main group atoms Q. The sheets are interconnected via M−Q bonds to a truly three-dimensional structure. Like in the isostructural ZrTiAs, the smaller 3d M atom prefers the site in the densely packed square planes. In addition to the dominating M−As bonds, the structure comprises strong M−M bonding. Independent of the exact Zr:V ratio, Zr_1−δV_1+δAs is calculated to have three-dimensional metallic properties.     

The crystal structure of Pd2B

The crystal structure of Pd₂B has been investigated by X-ray powder diffraction and single-crystal diffractometry. There are strong indications that Pd₂B crystallizes with the anti-CaCl₂ type structure (C 35), space group Pnnm (No. 58), a = 4.6918(4) Å, b = 5.1271(4) Å, and c = 3.1096(3) Å, but the extent to which the boron atoms assume ordered positions cannot be determined precisely with X-ray diffraction methods alone.     

Concerning the crystal structure of BrF3·AuF3

Crystals of the adduct, BrF₃·AuF₃, are monoclinic, with: a=5.356(4) Å, b=5.766(4) Å, c=8.649(3) Å, β=101.39(4)°, V=261.8(5) Å³, z=2, D_c=4.96 g/cm³. An ordered structure in P2₁ was found, but is of low precision (R₁=0.082) because of crystal deformation. The structure has planar BrF₄ units sharing F ligands cis with planar AuF₄ groups, each AuF₄ being similarly linked to two BrF₄. This generates a ribbon, creased at the bridging F along y, the gold on one side of the crease, the bromine on the other. Such ribbons are stacked parallel along y, with nearest neighbors related by twofold screw axes. This sandwiches each AuF₄ strip of a ribbon symmetrically between like strips. These contacts between the Au-strips bring up, to each Au-atom, two “non-bridging Au–F ligands” of each of the two neighboring strips, to give eight coordination in F. The bromine side of the creased ribbon is unsymmetrically sandwiched between a screw-axis related relative, and the edge of a Au-containing strip oriented almost perpendicular to it. This brings two non-bridging F of the nearest-strip BrF₄ and two non-bridging F of the AuF₄ strip into the secondary cordination sphere of the Br atom. Raman spectra of the BrF₃·AuF₃, molecular BrF₃, and polymeric AuF₃ suggest that the Br–F and Au–F stretching vibrations of BrF₃·AuF₃ are shifted slightly from those of the parent BrF₃ and AuF₃, and indicate some BrF₂⁺AuF₄⁻ character.     

Thermal stability and crystal structure of β-Ba3YB3O9

A new compound, β-Ba₃YB₃O₉, has been attained through solid phase transition from α-Ba₃YB₃O₉ at high temperatures. Differential thermal analysis (DTA) revealed the phase transition at about 1120°C, the melting temperature at about 1253°C. Its crystal structure has been determined from powder X-ray diffraction data. The refinement was carried out using the Rietveld method and the final refinement converged with R_p=10.5% and R_wp=13.7%. This compound belongs to the hexagonal space group R-3, with lattice parameters a=13.0441(1) Å and c=9.5291(1) Å. There are 6 formulas per unit cell and 7 atoms in the asymmetric unit. The structure of β-Ba₃YB₃O₉ is built up from Ba(Y)O₈, BaO₆ and YB₆O₁₈ units formed by one YO₆ octahedron and six BO₃ triangles with shared O atoms.     

The crystal structure of NaAs4O6Br

The crystal structure of NaAs₄O₆Br [a = 5.237(1), B = 8.043(1), C = 18.978(2) Å; space group Pmcn-D¹⁶_2h; Z = 4] was solved by a direct method strategy and was refined to an R value of 0.038 for 1515 intensities and 68 variables. The structure is characterized by neutrally charged and slightly waved As₂O₃ sheets arranged parallel to (001). These sheets are combined by the Na and Br atoms. The Na atom is coordinated to nine oxygen atoms and one bromine atom and the Br atom is coordinated to six arsenic atoms and one sodium atom. The compound NaAs₄O₆Br was synthesized by thermal treatment of NaBr and As₂O₃ in methanol solution [400(5) K, saturation vapor pressure].     

The crystal structure of Mg51Zn20

The crystal structure of Mg₅₁Zn₂₀, a phase designated conventionally as “Mg₇Zn₃,” has been determined by the single-crystal X-ray diffraction method. It was solved by the examination of a Patterson synthesis, and refined by the ordinary Fourier and least-squares method; the R value obtained was 4.8% for 1167 observed reflections. The crystal is orthorhombic, space group Immm, with a = 14.083(3), b = 14.486(3), c = 14.025(3) Å, and Z = 2. There are 18 independent atomic sites, Zn1Zn6, Mg1Mg10, A, and B, and the last two sites are statistically occupied by Zn and Mg atoms with the occupancies; 0.46(2)Zn7 + 0.52(2)Mg11 and 0.24(2)Zn8 + 0.74(2)Mg12, for A and B, respectively. The structure of the crystal is described as an arrangement of icosahedral coordination polyhedra, to which all the atomic sites but Zn3 site belong. In this arrangement the Zn atoms other than the Zn3 and Zn8(B) center the icosahedral coordination polyhedra with coordination number 12. The Zn3, Zn8 atoms, and all the Mg atoms except Mg11(A) are located at the centers of various coordination polyhedra with the coordination numbers from 11 to 15. The distances between neighboring atoms are 2.71–3.07, 2.82–3.65, and 2.60–3.20 Å for ZnZn, MgMg, and ZnMg, respectively.     

Preparation and crystal structure of Na2Mn2S3

Na₂Mn₂S₃ was prepared by reacting manganese powder with an excess of anhydrous sodium carbonate and elemental sulfur at 870 K. Extraction of the solidified melt with water and alcohol yielded well developed, bright red crystals. Na₂Mn₂S₃ crystallizes with a new monoclinic structure type, space group $\text{C2}\text{c}\text{, Z = 8}$, with a = 14.942(2)Å, b = 13.276(2)Å, c = 6.851(2)Å, and β = 116.50(1)°. The crystal structure was determined from single crystal diffractometer data and refined to a conventional R value of 0.026 for 1613 observed reflections. The atomic arrangement shows sulfur-manganese-sulfur slabs which are separated from each other by corrugated layers of sodium atoms. A prominent feature of the crystal structure is the formation of short, four-membered zigzag chains built up by MnS₄ tetradedra sharing edges. These chains are further connected by the remaining apices to form an infinite sheet. Short MnMn distances (3.02 and 3.05 Å, respectively) are found within the four membered chains. Susceptibility measurements show antiferromagnetic interactions between the Mn atoms.     

Single crystal growth and structure of La4Cu3MoO12

We report the synthesis and structure determination of single crystals of La₄Cu₃MoO₁₂ grown from a CuO/KCl flux. This material, whose structure had previously been reported based solely on polycrystalline diffraction data, shows frustrated magnetic behavior and an anti-ferromagnetic ordering of spin-1/2 triangles at low temperatures. The structural and atomic parameters determined from the single crystal data are in very good agreement with those reported previously. However, HREM data showed evidence for disorder in the stacking of the Cu₃MoO₄ planes, and thus a twinned structural refinement in space group P2₁/m was replaced by an equivalent disordered structural model in space group Pm. This development of a synthetic route to single crystals of La₄Cu₃MoO₁₂ will allow a more detailed investigation of its complex electronic and magnetic properties.