Crystal structure and phase transitions in perovskite-like C(NH2)3SnCl3

X-ray single-crystal diffraction, high-temperature powder diffraction and differential thermal analysis at ambient and high pressure have been employed to study the crystal structure and phase transitions of guanidinium trichlorostannate, C(NH₂)₃SnCl₃. At 295 K the crystal structure is orthorhombic, space group Pbca, Z=8, a=7.7506(2) Å, b=12.0958(4) Å and c=17.8049(6) Å, solved from single-crystal data. It is perovskite-like with distorted corner-linked SnCl₆ octahedra and with ordered guanidinium cations in the distorted cuboctahedral voids. At 400 K the structure shows a first-order order-disorder phase transition. The space group is changed to Pnma with Z=4, a=12.1552(2) Å, b=8.8590(2) Å and c=8.0175(1) Å, solved from powder diffraction data and showing disordering of the guanidinium cations. At 419 K, the structure shows yet another first-order order-disorder transformation with disordering of the SnCl₃⁻ part. The space group symmetry is maintained as Pnma, with a=12.1786(2) Å, b=8.8642(2) Å and c=8.0821(2) Å. The thermodynamic parameters of these transitions and the p-T phase diagram have been determined and described.     

Crystal structures of two new oxysulfides La5Ti2MS5O7 (M=Cu, Ag): evidence of anionic segregation

Two new compounds, La₅Ti₂MS₅O₇ (M=Cu, Ag) were synthesized and their structures solved from single crystal X-ray data. Both compounds are isotypic. They crystallize in the orthorhombic system (space group Pnma, Z=4) with lattice constants a=19.423(1) Å, b=3.9793(2) Å, c=18.1191(9) Å for La₅Ti₂CuS₅O₇, and a=19.593(2) Å, b=3.9963(1) Å, and c=18.2973(15) Å for La₅Ti₂AgS₅O₇. The structure of these compounds is built from fragments of the rock-salt, perovskite and fluorite types and a clear anionic segregation of the anions appears in the structure. La₅Ti₂CuS₅O₇ and La₅Ti₂AgS₅O₇ exhibit an orange-yellow color and measurement of their optical band gap gave 2.02 and 2.17 eV, respectively.     

Synthesis, phase relationship and crystal structure of the new binary compound Ir13Al45

The new phase Ir₁₃Al₄₅ was synthesized in equilibrium with an aluminum-rich melt. Its crystal structure was established from single-crystal diffraction data. The compound crystallizes in the space group Pnma and represents a novel structure type (Pearson symbol oP232, a=16.760(2) Å, b=12.321(1) Å, c=17.425(2) Å). The structure can essentially be described as a simple hexagonal column packing of pseudopentagonal columns formed by irregular Al polyhedra centered by Ir atoms. Ir₁₃Al₄₅ forms peritectically at 895 °C and exists in equilibrium with the melt in a narrow temperature interval of 19 °C.     

Ce10[Si10O9N17]Br, Nd10[Si10O9N17]Br and Nd10[Si10O9N17]Cl oxonitridosilicate halides with a new layered structure type

The isotypic oxonitridosilicate halides Ce₁₀[Si₁₀O₉N₁₇]Br, Nd₁₀[Si₁₀O₉N₁₇]Br and Nd₁₀[Si₁₀O₉N₁₇]Cl were obtained by the reaction of the respective lanthanide metals, their oxides and halides with “Si(NH)₂” in a radiofrequency furnace at temperatures around 1800 °C, using CsBr, resp. CsCl, as a flux. The crystal structures were determined by single-crystal X-ray diffraction (Pbam, no. 55, Z=2; Ce/Br: a=10.6117(9) Å, b=11.2319(10) Å, c=11.688(8) Å, R1=0.0356; Nd/Br: a=10.523(2) Å, b=11.101(2) Å, c=11.546(2) Å, R1=0.0239; Nd/Cl: a=10.534(2) Å, b=11.109(2) Å, c=11.543(2) Å, R1=0.0253) and represent a new layered structure type. The structure refinements were performed utilizing an O/N-distribution model according to Paulings rules, i.e. nitrogen was positioned on all bridging sites and mixed O/N-occupation was assumed on the terminal sites resulting in charge neutrality of the compounds. The layers consist of condensed [SiN₂(O/N)₂] and [SiN₃(O/N)] tetrahedra of Q² and Q³ type. The chemical composition of the compounds was derived from chemical analyses for Nd₁₀[Si₁₀O₉N₁₇]Br and electron probe micro analyses (EPMA) for all three compounds. The results of IR spectroscopic investigations are reported.     

Crystal structure and properties of the new vanadyl(IV)phosphates Na2MVO(PO4)2, M=Ca and Sr

Two new complex vanadyl(IV)phosphates Na₂MVO(PO₄)₂ (M=Ca, Sr) were synthesized in evacuated quartz ampoules and investigated by means of X-ray diffraction, electron microscopy, DTA, ESR and magnetic susceptibility measurements. The crystal structure of Na₂SrVO(PO₄)₂ was solved ab initio from X-ray powder diffraction data. Both compounds are isostructural: a=10.5233(3) Å, b=6.5578(2) Å, c=10.0536(3) Å and a=10.6476(3) Å, b=6.6224(2) Å, c=10.2537(3) Å for Ca and Sr, respectively; S.G. Pnma, Z=4. The compounds have a three-dimensional structure consisting of V⁴⁺O₆ octahedra connected by PO₄ tetrahedra via five of the six vertexes forming a framework with cross-like channels. The strontium and sodium atoms are located in the channels in an ordered manner. Electron diffraction as well as high-resolution electron microscopy confirmed the structure solution. The new vanadylphosphates are Curie-Weiss paramagnets in a wide temperature range down to 2 K with θ=12 and 5 K for Ca and Sr phases, respectively.     

Praseodymium magnetic contribution in the low temperature structure of Pr0.8Ca0.2MnO3

Magnetic and crystal structures of the manganite Pr_0.8Ca_0.2MnO₃ have been studied by neutron powder and single-crystal X-ray diffraction. Structure refinements using single crystal data [orthorhombic system, Pnma, (No. 62), a_RT=5.5534(3) Å, b_RT=7.6548(8) Å, c_RT=5.4400(5) Å, D_x=6.422 g cm⁻³, R^RT=0.029, R_w^RT=0.038] are consistent with a single domain sample. Structure and atomic displacement parameters exclude any electronic localization, even in a disordered way at 300 and 100 K. Low temperature electron diffraction observations do not show any trace of charge ordering.A Pr contribution to the magnetic structure has been shown with a maximum moment of 0.79 μ_B and spins alignments roughly along [101] orientations, at a lower temperature than the ferromagnetic transition observed at 130 K, due to Mn spins ordering.     

Sm2NiSn4: The intermediate structure type between ZrSi2 and CeNiSi2

A new rare earth nickel stannide, Sm₂NiSn₄, has been prepared by reacting the pure elements at high temperature in welded tantalum tubes. Its crystal structure was established by single crystal X-ray diffraction studies. Sm₂NiSn₄ crystallizes in the orthorhombic space group Pnma (No. 62) with cell parameters of a=16.878(2) Å, b=4.4490(7) Å, c=8.915(1) Å, and Z=4. Its structure can be viewed as the intermediate type between ZrSi₂ and CeNiSi₂. Sm₂NiSn₄ features two-dimensional (2D) corrugated [NiSn₄]⁶⁻ layers in which the 1D Sn zigzag chains and the 2D Sn square sheets are bridged by Ni atoms. The Sm³⁺ cations are located at the interlayer space. Results of both resistivity measurements and extended-Hückel tight-binding band structure calculations indicate that Sm₂NiSn₄ is metallic.     

K2Mo4O13 phases prepared by hydrothermal synthesis

Hydrothermal synthesis in the K-Mo oxide system was investigated as a function of the pH of the reaction medium. Four compounds were formed, including two K₂Mo₄O₁₃ phases. One is a new low-temperature polymorph, which crystallizes in the orthorhombic, space group Pbca, with Z=8 and unit cell dimensions a=7.544(1) Å, b=15.394(2) Å, c=18.568(3) Å. The other is the known triclinic K₂Mo₄O₁₃, whose structure was re-determined from single crystal data; its cell parameters were determined as a=7.976(2) Å, b=8.345(2) Å, c=10.017(2) Å, α=107.104(3)°, β=102.885(3)°, γ=109.760(3)°, which are the standard settings of the crystal lattice. The orthorhombic phase converts endothermically into triclinic phase at ca. 730 K with a heat of transition of 8.31 kJ/mol.     

Synthesis of Li(x)Na(2−x)Mn2S3 and LiNaMnS2 through redox-induced ion exchange reactions

Na₂Mn₂S₃ was oxidatively deintercalated using iodine in acetonitrile to yield Na_1.3Mn₂S₃, with lattice constants nearly identical to that of the reactant. Lithium was then reductively intercalated into the oxidized product to yield Li_0.7Na_1.3Mn₂S₃. When heated, this metastable compound decomposed to form a new crystalline compound, LiNaMnS₂, along with MnS and residual Na₂Mn₂S₃. Single crystal X-ray diffraction structural analysis of LiNaMnS₂ revealed that this compound crystallizes in P-3m1 with cell parameters a=4.0479(6) Å, c=6.7759(14) Å, V=96.15(3) Å³ (Z=1, wR2=0.0367) in the NaLiCdS₂ structure-type.     

Flux growth of a new cobalt-zinc-tin ternary phase Co7+xZn3−xSn8 and its relationship to CoSn

The intermetallic compound Co_7+xZn_3−xSn₈ (−0.2<x<0.2) forms from the reaction of cobalt in zinc/tin eutectic flux. This phase has a new structure type in orthorhombic space group Cmcm, with unit cell parameters a=4.138(1) Å, b=12.593(4) Å, and c=11.639(4) Å (Z=2; R₁=0.0301). Varying the amount of cobalt in the synthesis leads to formation of a superstructure in space group Pnma, with lattice parameters a=12.5908(2) Å, b=11.6298(3) Å, and c=8.2704(2) Å (Z=4; R₁=0.0347). A Co/Zn mixed site and a partially occupied Co site in the Cmcm structure order to form the Pnma supercell. TGA/DSC studies indicate that the binary phase CoSn initially forms in the flux at 1173 K, and then reacts with the zinc in the cooling solution to form the ternary structure at 823 K. This phase exhibits Pauli paramagnetic behavior.     

High-pressure high-temperature synthesis and crystal structure of the isotypic rare earth (RE)-thioborate-sulfides RE9[BS3]2[BS4]3S3, (RE=Dy-Lu)

Application of high-pressure high-temperature conditions (3.5 GPa at 1673 K for 5 h) to mixtures of the elements (RE:B:S=1:3:6) yielded crystalline samples of the isotypic rare earth-thioborate-sulfides RE₉[BS₃]₂[BS₄]₃S₃, (RE=Dy-Lu), which crystallize in space group P6₃ (Z=2/3) and adopt the Ce₆Al_3.33S₁₄ structure type. The crystal structures were refined from X-ray powder diffraction data by applying the Rietveld method. Dy: a=9.4044(2) Å, c=5.8855(3) Å; Ho: a=9.3703(1) Å, c=5.8826(1) Å; Er: a=9.3279(12) Å, c=5.8793(8) Å; Tm: a=9.2869(3) Å, c=5.8781(3) Å; Yb: a=9.2514(5) Å, c=5.8805(6) Å; Lu: a=9.2162(3) Å, c=5.8911(3) Å. The crystal structure is characterized by the presence of two isolated complex ions [BS₃]^3- and [BS₄]^5- as well as [□(S^2-)₃] units.     

A layered vanadium arsenate network decorated with the directly coordinated organonitrogen ligands: [V4O7(HAsO4)2(o-phen)2] (o-phen=o-phenanthroline)

A novel layered vanadium arsenate [V₄O₇(HAsO₄)₂(o-phen)₂] 1 (o-phen=o-phenanthroline) was synthesized by the hydrothermal reaction of V₂O₅, ZnCl₂, Na₂HAsO₄·7H₂O, o-phenanthroline (o-phen) and water. Its structure was determined by elemental analyses, ESR spectrum, XPS spectrum, TG analysis, IR spectrum and the single-crystal X-ray diffraction. Compound 1 crystallizes in monoclinic system, space group P2/c, a=10.122(2) Å, b=9.867(2) Å, c=15.367(3) Å, β=102.83(3)°, V=1496.4(5) Å³, Z=1, λ(MoKα)=0.71073 Å, (R(F)=0.0397 for 3422 reflections). Data were collected on a Rigaku R-AXIS RAPID IP diffractometer at 293 K in the range of 2.06°<θ<27.48°. The title compound contains an unusual two-dimensional (2D) As-V-O layer with four-, six- and eight-membered rings. The chelating o-phen ligands project perpendicularly above and below the undulating layer. 1 represents the first example of 2D inorganic vanadium arsenate backbone grafted with the directly coordinated organic ligands. Furthermore, the 3D supermolecular architecture is formed by π-π stacking interactions of the o-phen groups between adjacent layers.     

Crystal chemistry and crystallography of the SrR2CuO5 (R=lanthanides) phases

The crystal chemistry and crystallography of the compounds SrR₂CuO₅ (Sr-121, R=lanthanides) were investigated using the powder X-ray Rietveld refinement technique. Among the 11 compositions studied, only R=Dy and Ho formed the stable SrR₂CuO₅ phase. SrR₂CuO₅ was found to be isostructural with the “green phase”, BaR₂CuO₅. The basic structure is orthorhombic with space group Pnma. The lattice parameters for SrDyCuO₅ are a=12.08080(6) Å, b=5.60421(2) Å, c=7.12971(3) Å, V=482.705(4) Å³, and Z=8; and for the Ho analog are a=12.03727(12) Å, b=5.58947(7) Å, c=7.10169(7) Å, V=477.816(9) Å³, and Z=8. In the SrR₂CuO₅ structure, each R is surrounded by seven oxygen atoms, forming a monocapped trigonal prism (RO₇). The isolated CuO₅ group forms a distorted square pyramid. Consecutive layers of prisms are stacked in the b-direction. Bond valence calculations imply that residual strain is largely responsible for the narrow stability of the SrR₂CuO₅ phases with R=Dy and Ho only. X-ray powder reference diffraction patterns for SrDy₂CuO₅ and SrHo₂CuO₅ were determined.     

Synthesis, structure, and optical properties of the new lanthanum copper oxysulfide La3CuO2S3

The new quaternary lanthanum copper oxysulfide La₃CuO₂S₃ has been synthesized by the reaction of La₂S₃ and CuO at 1223 K. This compound crystallizes in space group Pnma of the orthorhombic system with four formula units in a cell of dimensions at 153 K of a=14.0318(7) Å, b=3.9342(2) Å, and c=12.5212(6) Å. The structure of La₃CuO₂S₃ consists of a three-dimensional framework of interconnected LaO_nS_8−n bicapped trigonal prisms and CuS₄ tetrahedra. Optical absorption measurements on a La₃CuO₂S₃ single crystal led to derived band gaps of 2.01 eV in both the [010] and [001] directions.     

R12Pt7In (R=Ce, Pr, Nd, Gd, Ho)—new derivatives of the Gd3Ga2-type

A new compound Ce₁₂Pt₇In was synthesized and its crystal structure at 300 K has been determined from single crystal X-ray data. It is tetragonal, space group I4/mcm, Z=4, with the lattice parameters: a=12.102(1) Å and c=14.542(2) Å, wR2=0.1102, 842 F² values, 33 variable parameters. The structure of Ce₁₂Pt₇In is a fully ordered ternary derivative of the Gd₃Ga₂-type. Isostructural compounds has been found to form with Pr (a=11.976(1) Å, c=14.478(2) Å), Nd (a=11.901(1) Å, c=14.471(2) Å), Gd (a=11.601(3) Å, c=14.472(4) Å), and Ho (a=11.369(1) Å, c=14.462(2) Å). Magnetic properties of Ce₁₂Pt₇In, Pr₁₂Pt₇In and Nd₁₂Pt₇In were studied down to 1.7 K. All three ternaries order magnetically at low temperatures with complex spin arrangements. The electrical resistivity of Ce₁₂Pt₇In and Nd₁₂Pt₇In is characteristic of rare-earth intermetallics.     

Crystal and magnetic structures of the brownmillerite compound Ca2Fe1.039(8)Mn0.962(8)O5

The crystal and magnetic structures of the brownmillerite material, Ca₂Fe_1.039(8)Mn_0.962(8)O₅ were investigated using powder X-ray and neutron diffraction methods, the latter from 3.8 to 700 K. The compound crystallizes in Pnma space group with unit cell parameters of a=5.3055(5) Å, b=15.322(2) Å, c=5.4587(6) Å at 300 K. The neutron diffraction study revealed the occupancies of Fe³⁺ and Mn³⁺ ions in both octahedral and tetrahedral sites and showed some intersite mixing and a small, ∼4%, Fe excess. While bulk magnetization data were inconclusive, variable temperature neutron diffraction measurements showed the magnetic transition temperature to be 407(2) K below which a long range antiferromagnetic ordering of spins occurs with ordering wave vector k=(000). The spins of each ion are coupled antiferromagnetically with the nearest neighbors within the same layer and coupled antiparallel to the closest ions from the neighboring layer. This combination of intra- and inter-layer antiparallel arrangement of spins forms a G-type magnetic structure. The ordered moments on the octahedral and tetrahedral sites at 3.8 K are 3.64(16) and 4.23(16) μ_B, respectively.     

Synthesis, crystal structures and photoluminescence properties of new oxyborates, Mg5NbO3(BO3)3 and Mg5TaO3(BO3)3, with novel warwickite-type superstructures

Single crystals of new oxyborates, Mg₅NbO₃(BO₃)₃ and Mg₅TaO₃(BO₃)₃, were prepared at 1370 °C in air using B₂O₃ as a flux. They were colorless and transparent with block shapes. X-ray diffraction analysis of the single crystals revealed Mg₅NbO₃(BO₃)₃ and Mg₅TaO₃(BO₃)₃ to be isostructural. The X-ray diffraction reflections were indexed to the orthorhombic Pnma (No. 62) system with a=9.3682(3) Å, b=9.4344(2) Å, c=9.3379(3) Å and Z=4 for Mg₅NbO₃(BO₃)₃ and a=9.3702(3) Å, b=9.4415(3) Å, c=9.3301(2) Å and Z=4 for Mg₅TaO₃(BO₃)₃. The crystal structures of Mg₅NbO₃(BO₃)₃ and Mg₅TaO₃(BO₃)₃ are novel warwickite-type superstructures having ordered arrangements of Mg and Nb/Ta atoms. Polycrystals of Mg₅NbO₃(BO₃)₃ prepared by solid state reaction at 1200 °C in air showed broad blue-to-green emission with a peak wavelength of 470 nm under 270 nm ultraviolet excitation at room temperature.     

Crystal structure and magnetic properties of Co2TeO3Cl2 and Co2TeO3Br2

The crystal structures of the two new synthetic compounds Co₂TeO₃Cl₂ and Co₂TeO₃Br₂ are described together with their magnetic properties. Co₂TeO₃Cl₂ crystallize in the monoclinic space group P2₁/m with unit cell parameters a=5.0472(6) Å, b=6.6325(9) Å, c=8.3452(10) Å, β=105.43(1)°, Z=2. Co₂TeO₃Br₂ crystallize in the orthorhombic space group Pccn with unit cell parameters a=10.5180(7) Å, b=15.8629(9) Å, c=7.7732(5) Å, Z=8. The crystal structures were solved from single crystal data, R=0.0328 and 0.0412, respectively. Both compounds are layered with only weak interactions in between the layers. The compound Co₂TeO₃Cl₂ has [CoO₄Cl₂] and [CoO₃Cl₃] octahedra while Co₂TeO₃Br₂ has [CoO₂Br₂] tetrahedra and [CoO₄Br₂] octahedra. The Te(IV) atoms are tetrahedrally [TeO₃E] coordinated in both compounds taking the 5s² lone electron pair E into account. The magnetic properties of the compounds are characterized predominantly by long-range antiferromagnetic ordering below 30 K.     

Crystal structure and magnetic properties of Na2Ni(HPO3)2

Na₂Ni(HPO₃)₂, obtained as light yellow-green crystals under mild hydrothermal conditions, crystallizes in the orthorhombic Pnma space-group with lattice parameters: a=11.9886(3), b=5.3671(2), c=9.0764(3) Å, V=584.01 Å³, Z=4. The structure consists of zig-zag chains of NiO₆ octahedra bridged by two HPO₃²⁻ and the chains are further connected through HPO₃²⁻ to four nearest chains to form a three dimensional framework, delimiting intersecting tunnels in which the sodium ions are located. The Na cations reside in the irregular Na(1)O₅, Na-O of 2.276-2.745 Å, and Na(2)O₉, Na-O of 2.342-2.376 Å, environments. The presence of the phosphite monoanion has been further confirmed by IR spectroscopy. Due to the 3D framework of Ni connected by O-P-O bridges, the magnetic susceptibility behaves as a paramagnet above 100 K (C=1.49(2) emu K mol⁻¹, μ_eff=3.45 μ_B, Θ=−39(2) K) and below 6 K, it orders antiferromagnetically as confirmed the sharp drop and the non-Brillouin behavior of the isothermal magnetization at 2 K.     

Synthesis, crystal structures, magnetic and electric transport properties of Eu11InSb9 and Yb11InSb9

Two new rare-earth metal containing Zintl phases, Eu₁₁InSb₉ and Yb₁₁InSb₉ have been synthesized by reactions of the corresponding elements in molten In metal to serve as a self-flux. Their crystal structures have been determined by single crystal X-ray diffraction—both compounds are isostructural and crystallize in the orthorhombic space group Iba2 (No. 45), Z=4 with unit cell parameters a=12.224(2) Å, b=12.874(2) Å, c=17.315(3) Å for Eu₁₁InSb₉, and a=11.7886(11) Å, b=12.4151(12) Å, c=16.6743(15) Å for Yb₁₁InSb₉, respectively (Ca₁₁InSb₉-type, Pearson's code oI84). Both structures can be rationalized using the classic Zintl rules, and are best described in terms of discrete In-centered tetrahedra of Sb, [InSb₄]⁹⁻, isolated Sb dimers, [Sb₂]⁴⁻, and isolated Sb anions, Sb³⁻. These anionic species are separated by Eu²⁺ and Yb²⁺ cations, which occupy the empty space between them and counterbalance the formal charges. Temperature-dependent magnetic susceptibility and resistivity measurements corroborate such analysis and indicate divalent Eu and Yb, as well as poorly metallic behavior for both Eu₁₁InSb₉ and Yb₁₁InSb₉. The close relationships between these structures and those of the monoclinic α-Ca₂₁Mn₄Sb₁₈ and Ca₂₁Mn₄Bi₁₈ are also discussed.