Crystal structure of complex natural aluminum magnesium calcium iron oxide

The structure of a new natural oxide found near the Tashelga River (Eastern Siberia) was studied by X-ray diffraction. The pseudo-orthorhombic unit cell parameters are a = 5.6973(1) Å, b = 17.1823(4) Å, c = 23.5718(5) Å, β = 90°, sp. gr. Pc. The structure was refined to R = 0.0516 based on 4773 reflections with |F| > 7σ(F) taking into account the twin plane perpendicular to the z axis (the twin components are 0.47 and 0.53). The crystal-chemical formula (Z = 4) is Ca₂Mg ₂ ^IV Fe ₂ ^(2+)IV [Al ₁₄ ^VI O₃₁(OH)][Al ₂ ^IV O][Al^IV]AL^IV(OH)], where the Roman numerals designate the coordination of the atoms. The structure of the mineral is based on wide ribbons of edge-sharing Al octahedra (an integral part of the spinel layer). The ribbons run along the shortest x axis and are inclined to the y and z axes. The adjacent ribbons are shifted with respect to each other along the y axis, resulting in the formation of step-like layers in which the two-ribbon thickness alternates with the three-ribbon thickness. Additional Al octahedra and Mg and Fe²⁺ tetrahedra are located between the ribbons. The layers are linked together to form a three-dimensional framework by Al tetrahedra, Ca polyhedra, and hydrogen bonds with the participation of OH groups.     

Crystal structure of 2,4,6-trinitropyridine and its N-oxide

The structures of 2,4,6-trinitropyridine (TNPy) and its N-oxide were determined by X-ray single crystal diffraction. TNPy and 2,4,6-trinitropyridine-1-oxide (TNPyO) crystallize in space groupPbcn andPnma, respectively. The crystallographic parameters are as follows: TNPy,a = 28.573(6) Å,b = 9.7394(19) Å, andc = 8.7566(18) Å, α = β = γ = 90^°, μ = 0.164 mm^?1,V = 2436.8(8) ų,z = 12,Dx = 1.751 mg/mm³,F(000) = 1296,T = 293(2) K, 1.43^°≤ θ≤ 27.40^°, the finalR factor:R ₁ = 0.0574,wR ₂ = 0.1337. TNPyO,a = 9.6272(19) Å,b = 14.128(3) Å, andc = 5.9943(12) Å, α = β = γ = 90^°, μ = 0.179 mm^?1,V = 815.3(3)ų,z = 4,Dx = 1.875 mg/mm³,F(000) = 464,T = 293(2) K, 2.88^°≤ θ≤ 27.44^°, the finalR factor:R ₁ = 0.0497,wR ₂ = 0.1515.     

Crystal structure of a new representative of the cancrinite group with a 12-layer stacking sequence of tetrahedral rings

The crystal structure of a 12-layer tounkite-like mineral of the cancrinite group was determined for the first time by single-crystal X-ray diffraction analysis (the unit-cell parameters are a = 12.757 Å, c = 32.211 Å). The structure was refined in the space group P3 to R = 0.035 using 3834 reflections with | F| > 2σ(F). Si and Al atoms occupy tetrahedral framework positions in an ordered fashion. The average distances in the tetrahedra are 〈Si-O〉 = 1.611 Å and 〈Al-O〉 = 1.723 Å. The stacking sequence of the layers is described as CACACBCBCACB, where A, B, and C are six-membered rings arranged around the [2/3 1/3 z], [1/3 2/3 z], and [0 0 z] axes, respectively. In the structure of the mineral, the columns along the [0 0 z] axis are composed of cancrinite cages. The columns along the [2/3 1/3 z] and [1/3 2/3 z] axes contain alternating cancrinite, bystrite, and liottite cages.     

Gallium vacancy ordering in Ga<Subscript>2</Subscript>Se<Subscript>3</Subscript> thin layers on Si(100), Si(111), and Si(123) substrates

Thin Ga₂Se₃ layers deposited on silicon substrates with the (100), (111), and (123) orientations are studied by transmission electron microscopy and X-ray microanalysis. Some features and regularities of the stoichiometric gallium vacancy ordering at different substrate orientations are discussed. The Ga₃Se₄(100)с(2 × 2) and Ga₂Se₃(111)(√3 × √3)-R30° ordered structures are formed on the Si(100) and Si(111) surfaces, respectively.     

Structural chemistry of peroxo compounds of group VI transition metals: I. Peroxo complexes of chromium (a review)

The specific features revealed in the structure of the d ³ Cr(III), d ² Cr(IV), d ¹Cr(V), and d ⁰ Cr(VI) peroxo complexes with the ratios M:O₂ = 1:1, 1:2, and 1:4 are considered. It is noted that, in eleven compounds of the general formula Cr(O₂)_nO_m A _p (n = 1, 2, 4; m = 0, 1; p = 0–4), the metal atoms can be in four oxidations states: +3 (d ³), +4 (d ⁴), +5 (d ¹), and +6 (d ⁰). This property distinguishes chromium peroxo compounds from molybdenum and tungsten dioxygen complexes, which, with one exception, are represented by the d ⁰ M(VI) compounds.     

Study of the amorphization of surface silicon layers implanted by low-energy helium ions

The structural changes in surface layers of Si(001) substrates subjected to plasma-immersion implantation by (2–5)-keV helium ions to a dose of D = 6 × 10¹⁵–5 × 10¹⁷ cm^–2 have been studied by highresolution X-ray diffraction, Rutherford backscattering, and spectral ellipsometry. It is found that the joint application of these methods makes it possible to determine the density depth distribution ρ(z) in an implanted layer, its phase state, and elemental composition. Treatment of silicon substrates in helium plasma to doses of 6 × 10¹⁶ cm^–2 leads to the formation of a 20- to 30-nm-thick amorphized surface layer with a density close to the silicon density. An increase in the helium dose causes the formation of an internal porous layer.     

Synthesis and structure of Cs[UO<Subscript>2</Subscript>(SeO<Subscript>4</Subscript>)(OH)] · <Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O (<Emphasis Type="Italic">n</Emphasis> = 1.5 or 1)

The synthesis and single-crystal X-ray diffraction study of Cs[UO₂(SeO₄)(OH)] · 1.5H₂O (I) and Cs[UO₂(SeO₄)(OH)] · H₂O (II) are performed. Compound I crystallizes in the monoclinic crystal system, a = 7.2142(2) Å, b = 14.4942(4) Å, c = 8.9270(3) Å, β = 112.706(1)°, space group P2₁/m, Z = 4, and R = 0.0222. Compound II is monoclinic, a = 8.4549(2) Å, b = 11.5358(3) Å, c = 9.5565(2) Å, β = 113.273(1)°, space group P2₁/c, Z = 4, and R = 0.0219. The main structural units of crystals I and II are [UO₂(SeO₄)(OH)]^? layers which belong to the AT ³ M ² crystal chemical group of uranyl complexes (A = UO ₂ ²⁺ , T ³ = SeO₄ ^2?, and M ² = OH^?). In structure I, johannite-like layers are found. Structure II is a topological isomer of I. The two structures differ in the number of U(VI) atoms bound to the central atom by all bridging ligands.     

Synthesis and an X-ray diffraction study of Rb<Subscript>2</Subscript>[(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>3</Subscript>]

The synthesis and X-ray diffraction study of compound Rb₂[(UO₂)₂(C₂O₄)₃], which crystallizes in the monoclinic crystal system, are performed. The unit cell parameters are as follows: a = 7.9996(6) Å, b = 8.8259(8) Å, c = 11.3220(7) Å, β = 105.394(2)°, and V = 770.7(1) ų; space group P2₁/n, Z = 2, and R ₁ = 0.0271. [(UO₂)₂(C₂O₄)₃]^2? layers belonging to the AK _0.5 ⁰² T ¹¹ crystal chemical group of uranyl complexes (A = UO ₂ ²⁺ , K ⁰² = C₂O ₄ ^2? , and T ¹¹ = C₂O ₄ ^2? ) are uranium-containing structural units of the crystals. The layers are connected with outer-sphere rubidium cations by electrostatic interactions.     

Synthesis and structure of (Rb<Subscript>0.50</Subscript>Ba<Subscript>0.25</Subscript>)[UO<Subscript>2</Subscript>(CH<Subscript>3</Subscript>COO)<Subscript>3</Subscript>]

A new compound (Rb_0.50Ba_0.25)[UO₂(CH₃COO)₃] is synthesized and its crystal structure is studied by X-ray diffraction. The compound crystallizes in the form of yellow plates belonging to the cubic crystal system. The unit cell parameter a = 17.0367(1) Å, V = 4944.89(5) ų, space group I \(\bar 4\)3d, Z = 16, and R = 0.0182. The coordination polyhedron of the uranium atom is a hexagonal bipyramid with oxygen atoms of three acetate groups and the uranyl group in the vertices. The crystal chemical formula of the uranium-containing group is AB ₃ ⁰¹ (A = UO ₂ ²⁺ , B ⁰¹ = CH₃COO^?). The oxygen atoms of the acetate groups that enter the coordination polyhedron of uranium are bound to barium and rubidium atoms.     

Refinement of the crystal structures of synthetic nickel- and cobalt-bearing tourmalines

The crystal structures of synthetic tourmalines with a unique composition containing 3d elements (Ni, Fe, and Co) have been refined: (Ca_0.12?_0.88)(Al_1.69Ni _0.81 ²⁺ Fe _0.50 ²⁺ )(Al_5.40Fe _0.60 ³⁺ )(Si_5.82Al_0.18O₁₈)(BO₃)₃(OH)_3.25O_0.75 I, a = 15.897(5), c = 7.145(2) Å, V = 1564(1) Å; Na_0.91(Ni _1.20 ²⁺ Cr _0.96 ³⁺ Al_0.63Fe _0.18 ²⁺ Mg_0.03)(Al_4.26Ni _1.20 ²⁺ Cr _0.48 ³⁺ Ti_0.06)(Si_5.82Al_0.18)O₁₈(BO₃)₃(OH)_3.73O_0.27 II, a = 15.945(5), c = 7.208(2) Å, V = 1587(1) ų and Na_0.35(Al_1.80Co _1.20 ²⁺ )(Al_5.28Co _0.66 ²⁺ Ti_0.06)(Si_5.64B_0.36)O₁₈(BO₃)₃(OH)_3.81O_0.19 III, a = 15.753(8), c = 7.053(3) Å, V = 1516(2) ų. The reliability factors are R ₁ = 0.038?0.057 and wR ₂ = 0.041–0.060. It is found that 3d elements occupy both Y- and Z positions in all structures. The excess positive charge is compensated for due to the incorporation of divalent oxygen anions into the O3(V)+O1(W) positions.     

X-ray diffraction study of Rb<Subscript>2</Subscript>[(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>(CrO<Subscript>4</Subscript>)<Subscript>3</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>] · 4H<Subscript>2</Subscript>O

The compound Rb₂[(UO₂)₂(CrO₄)₃(H₂O)₂] · 4H₂O was studied by X-ray diffraction. The crystals are monoclinic, a = 10.695(2) Å, b = 14.684(3) Å, c = 14.125(3) Å, β = 108.396(4)°, sp. gr. P2₁/c, Z = 4, V = 2104.9(7) ų, and R = 0.0491. The main structural units are layers consisting of [(UO₂)₂(CrO₄)₃(H₂O)₂]^2? anions belonging to the crystal-chemical group A ₂ T ₂ ³ B ²M ₂ ¹ (A = UL ₂ ²⁺ , T ³ and B ² are CrO ₄ ^2? , and M ¹ is H₂O) of uranyl complexes. The uranium-containing layered groups are held together by electrostatic interactions with rubidium cations, as well as by hydrogen bonds with the participation of inner- and outer-sphere water molecules.     

Synthesis,Spectroscopic and Crystal Structure Analysis of <Emphasis Type="Italic">N</Emphasis>-[imidazolidin-2-ylidene]-5-(thien-2-yl)[1,3,4]thiadiazole-2-amine

The crystal structure of the title compound has been determined. The compound crystallizes in the monoclinic space group P2₁/c with a = 5.9885(2) Å, b = 14.7345(4) Å, c = 12.3719(4) Å, β = 96.655(5)°, V = 1084.31(8) Å³, z = 4. An intramolecular N–H···N hydrogen bond forms a pseudo-six-membered ring with graph set S ¹ ₁(6). The crystal structure is stabilized by intermolecular interactions of the type N–H···N and C–H···N. The packing motifs in accordance with Etter’s analysis are R ² ₂(8) corresponding to N–H···N dimer and that generated by the chain is C(7).     

Crystal structure of a new synthetic Ca,Li pentaborate: CaLi<Subscript>4</Subscript>[B<Subscript>5</Subscript>O<Subscript>8</Subscript>(OH)<Subscript>2</Subscript>]<Subscript>2</Subscript>

When studying the phase formation in the CaO-Li₂O-B₂O₃-H₂O system, a new Ca,Li pentaborate was synthesized under hydrothermal conditions. The structure of a new compound with the crystallochemical formula CaLi₄[B₅O₈(OH)₂]₂ (sp. gr. Pb2n, a = 8.807(7), b = 9.372(7), c = 8.265(6) Å, V = 682.2(9) ų, Z = 2, d_calcd = 2.43 g/cm³, automated SYNTEX-\(P\bar 1\) diffractometer, 2690 reflections, 2θ/θ scan, λMo) is refined up to R_hkl = 0.0557 in the anisotropic approximation of atomic thermal vibrations with allowance for the localized H atoms. The structure of the Ca,Li pentaborate is formed by (010) open boron—oxygen layers formed by two independent [B₅O₈(OH)₂]^3? pentagroups, with each of them being formed by three B tetrahedra and two B triangles. The structure framework consists of the above boron—oxygen layers bound by isolated Li tetrahedra. The Ca cations are localized in the centers of eight-vertex polyhedra located in the [001] channels of the Li,B,O framework. Comparative crystallochemical analysis of the new Ca,Li pentaborate and Li pentaborate of the composition Li₃[B₅O₈(OH)₂]-II showed that the anionic matrices of both compounds are completely identical, whereas some of the cationic positions are different.     

Birefringence of (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>SO<Subscript>4</Subscript> crystals under the action of uniaxial pressures

The influence of uniaxial mechanical pressure σ _m ≤ 150 bar on the spectral (300–800 nm) dependence of the birefringence Δn _i of (NH₄)₂SO₄ crystals is studied. The dispersion Δn _i (λ) is shown to be normal and greatly increases when approaching the absorption edge. Uniaxial pressure changes the value of dispersion dΔn _i /dλ but not its character. It is found that the simultaneous action of pressures σ _x ～ σ y ～ 560 bar results in the occurrence of a uniaxial isotropic state. Piezoelectric constants of the crystals are estimated.     

Synthesis and structure of a 2D Zn complex with mixed ligands stacked in offset ABAB manner

The title complex, {[Zn(ODIB)_1/2(bpdc)]·2DMF}_n was prepared under hydrothermal conditions (dimethylformamide and water) based on two ligands, namely, 1,1′-oxy-bis[3,5-diimidazolyl-benzene] (ODIB) and biphenyldicarboxylic acid (H₂bpdc). ODIB ligands link Zn cations to give layers in crystal. bpdc^2– anions coordinate to Zn atoms, however, their introduction does not increase the dimension of the structure. Each layer is partially passes through the adjacent layers in the offset ABAB manner.     

Conditions for stabilization of the ordered state of cations in complex oxides with perovskite structure

Analytical expressions for the coefficients in the Landau potential for six types of ordering of complex oxides with perovskite structure in terms of the sums of ordering energies in different coordination spheres are obtained in the approximation of effective pair interactions. On the basis of the pair interaction potentials of the form v(r) = ?1/r⁶ + Acos(qr)/(qr)³, the conditions for q and R are established, which lead to stabilization of the ordered phases.     

Raman spectroscopy study of the structure of gallium nitride epitaxial layers of different orientations

The composition nonstoichiometry and structural quality of undoped gallium nitride layers grown by the hydride vapor phase epitaxy on sapphire substrates of different orientations have been estimated using Raman spectroscopy. It is found for the first time that the peak position of the phonon mode E₂(high) in the Raman spectra of gallium nitride films at a wave vector of 572 cm^–1 depends on the initial orientation of sapphire substrate and is low-frequency shifted when passing from Ga-polar to partially N-polar orientation. Additional modes are found in the spectra of GaN layers grown on substrates with m and r orientations. It is shown that a decrease in the composition deviation from stoichiometry, caused by reducing the HCl flow through the gallium source during the growth of GaN layers, leads to an increase in the phonon-mode intensity in the Raman spectrum.     

Coordination dimers constructed from metal(II) halides and the organic ligand 1,2-dimethoxy- 4,5-bis(2-pyridylethynyl)benzene

A series of new coordination compounds has been synthesized using the organic ligand 1,2-dimethoxy-4,5-bis(2-pyridylethynyl)benzene (dmpeb). The compounds all form dimers consisting of two metal cations bridged by two ligand molecules. Charge balance is provided by halide ligands, and the four-coordinate metal centers are distorted from the ideal tetrahedral environment. [CoCl₂(dmpeb)]₂ (1) crystallizes in the monoclinic space group P2₁/n with a = 8.5272(6) Å, b = 18.3653(13) Å, c = 13.3493(9) Å, β = 103.574(2)^°, V = 2032.2(2) ų, Z = 2. [ZnCl₂(dmpeb)]₂ (2) is isostructural to 1 and has the cell parameters a = 8.5495(4) Å, b = 18.4049(8) Å, c = 13.3692(6) Å, β = 103.4460(10)^°, V = 2046.01(16) ų, Z = 2. [ZnBr₂(dmpeb)]₂ (3) is also isostructural to 1 with a = 8.7882(5) Å, b = 18.7260(12) Å, c = 13.3857(8) Å, β = 102.5990(10)^°, V = 2149.8(2) ų, Z = 2. Additionally, the compounds [ZnI₂(dmpeb)]₂ (4, cell parameters: a = 8.9650(5) Å, b = 19.1251(10) Å, c = 13.4160(7) Å, β = 101.1660(10)^°, V = 2256.7(2) ų, Z = 2), [HgCl₂(dmpeb)]₂ (5, cell parameters: a = 8.8457(7) Å, b = 18.4030(15) Å, c = 13.3711(11) Å, β = 104.246(2)^°, V = 2109.7(3) ų, Z = 2), and [HgBr₂(dmpeb)]₂ (6, cell parameters: a = 9.0576(5) Å, b = 18.8634(11) Å, c = 13.4535(8) Å, β = 102.9780(10)^°, V = 2239.9(2) ų, Z = 2) are also isostructural to 1. A seventh dimeric compound, [HgI₂(dmpeb)]₂, not isostructural to the others was also characterized by X-ray crystallography. [HgI₂(dmpeb)]₂ (7) crystallizes in the triclinic space group P-1 with a = 8.8028(5) Å, b = 12.0990(7) Å, c = 12.4082(7) Å, α = 109.7240(10)^°, β = 107.3680(10)^°, γ = 93.0880(10)^°, V = 1169.57(12) ų, Z = 1.     

Pyroxenoids of pyroxmangite–pyroxferroite series from xenoliths of Bellerberg paleovolcano (Eifel,Germany): Chemical variations and specific features of cation distribution

The pyroxferroite and pyroxmangite from xenoliths of aluminous gneisses in the alkaline basalts of Bellerberg paleovulcano (Eifel, Germany) have been studied by electron-probe and X-ray diffraction methods and IR spectroscopy. The parameters of the triclinic unit cells are found to be a = 6.662(1) Å, b = 7.525(1) Å, c = 15.895(2) Å, α = 91.548(3)°, β = 96.258(3)°, and γ = 94.498(3)° for pyroxferroite and a = 6.661(3) Å, b = 7.513(3) Å, c = 15.877(7) Å, α = 91.870(7)°, β = 96.369(7)°, and γ = 94.724(7)° for pyroxmangite; sp. gr. \(P\overline 1 \). The crystallochemical formulas (Z = 2) are, respectively, ^M(1–2)(Mn_0.5Ca_0.4Na_0.1)₂^M(3–6)(Fe, Mn)₄^M7[Mg_0.6(Fe, Mn)_0.4][Si₇O₂₁] and ^M(1–3)(Mn, Fe)₃^M(4–6)[(Fe, Mn)_0.7Mg_0.3]₃^M7[Mg_0.5(Fe, Mn)_0.5][Si₇O₂₁]. For these and previously studied representatives of the pyroxmangite structural type, an analysis of the cation distribution over sites indicates wide isomorphism of Mn²⁺, Fe²⁺, and Mg in all cation M(1–7) sites and the preferred incorporation of Сa and Na into large seven-vertex M1O₇ and M2O₇ polyhedra and Mg into the smallest five-vertex M7O₅ polyhedron.     

Crystal chemistry of KCuMn<Subscript>3</Subscript>(VO<Subscript>4</Subscript>)<Subscript>3</Subscript> in the context of detailed systematics of the alluaudite family

The crystal structure of new manganese potassium copper vanadate KCuMn₃(VO₄)₃, which was prepared by the hydrothermal synthesis in the K₂CO₃–CuO–MnCl₂–V₂O₅–H₂O system, was studied by X-ray diffraction (R = 0.0355): a = 12.396(1) Å, b = 12.944(1) Å, c = 6.9786(5) Å, β = 112.723(1)°, sp. gr. C2/c, Z = 4, ρ_calc = 3.938 g/cm³. A comparative analysis of the crystal-chemical features of the new representative of the alluaudite family and related structures of minerals and synthetic phosphates, arsenates, and vanadates of the general formula A(1)A(1)′A(1)″A(2)A(2)′M(1)M(2)₂(TO₄)₃ (where A are sites in the channels of the framework composed of MО₆ octahedra and TО₄ tetrahedra) was performed. A classification of these structures into subgroups according to the occupancy of A sites is suggested.