Cation distribution in the structure of titanium-containing ludwigite

The crystal structure of natural titanium-containing ludwigite has been refined. The unit-cell parameters are a = 9.260 ± 0.002 Å, b = 12.294± 0.002 Å, c = 3.0236± 0.0005 Å, sp. gr. Pbam, and R = 0.0288. The observed cation distribution over the M1-M4 positions corresponds to the structural formula (Mg_0.5)(Mg_1.0)(Mg_0.338Fe _0.162 ²⁺ )(Fe _0.47 ³⁺ Ti _0.21 ⁴⁺ Mg _0.15 ²⁺ Al _0.10 ³⁺ Fe _0.07 ²⁺ (BO₃)O₂. Highly charged titanium ions in the M4 position are balanced mainly with magnesium and not with divalent iron ions.     

Phase states of the gypsum thermal-annealing derivatives according to electron spin resonance spectra

The electron spin resonance (ESR) spectra of SO ₃ ^? and SO ₂ ^? radical ions with a linewidth ΔH ≈ 2.7 G and SO ₃ ^? (A ₁) and SO ₃ ^? (A ₂) centers with superhyperfine splitting due to the interaction with protons in platelike gypsum single crystals under X-ray irradiation have been analyzed at 25°C. Dehydrated regions with a radius >4 Å are revealed in gypsum. The ESR spectra of SO ₃ ^? radical ions and atomic hydrogen with ΔH ≈ 0.3 G are found in the products of isothermal annealing of gypsum kept for 30 min after X-ray irradiation at 25°C. The dependences of the intensities of these spectra on the annealing temperature are studied in the range of 100–450°C. The temperature range of formation of α- and β-phase states of bassanite and γ-anhydrite are determined. The process of residual water redistribution between the channel systems of the α- and β-phase types of γ-CaSO₄ in gypsum thermal derivatives is established.     

Derivation of the conditions for equivalent positions in crystals: The dissymmetrization of barite by electron spin resonance spectra

The conditions for equivalent positions on the (hkl) face of growing crystal are derived using symmetry elements of the space group. It is shown by the example of the sp. gr. D _2h ¹⁶ that the conditions of equivalent position formation coincide with conditions of the reflection of diffracted beams by crystal. It is established that electron spin resonance (ESR) centers in barite, SO ₄ ^? (I) and SO ₄ ^? (II), with only two conjugate spectra with equal intensity out of four, and SO ₄ ^? (III), with a different intensity of conjugate spectra K _??M = 2, are localized into the growth pyramid of the (001) face with a [010] step. SO ₂ ^? , SO ₃ ^? ,, and SO ₄ ^? (IV) centers, having an identical intensity of the conjugate ESR spectra with K _??M = 2, are localized into the growth pyramid of the (210) face with a growth step [001].     

Crystallochemical modeling, synthesis, and study of new tantalum and niobium phosphates with a framework structure

A crystallochemical approach is used to model the compositions of phosphates of pentavalent elements with the expected structure. New phosphates with a framework structure of the T ₂ ^I T ₃ ^2/III T ₁ ^2/V (PO₄)₃ type (T ^I = Na or K; T ^III = Al, Cr, or Fe; and T ^V = Nb or Ta) are synthesized and characterized by X-ray diffraction analysis (including high-temperature diffraction) and IR spectroscopy. It is established that, depending on the nature of the alkali cation (Na or K), these compounds are crystallized in two structural modifications: rhombohedral and cubic (sp. gr. R $\bar 3$ c and P2₁3, respectively). The unit-cell parameters and the thermal expansion coefficients of the phosphates under study are determined and the dependences of these characteristics on the nature of cations are established.     

Crystal chemistry of Li,GeVI-germanates: Combinatorial-topological analysis and modeling of crystal structures

The combinatorial-topological analysis of the structures of framework Li,Ge-germanates of the compositions Li₂Ge^VIGe ₂ ^IV O₆(OH)₂ (sp. gr. B ₂/b), Li₂Ge^VIGe ₃ ^IV O₉ (sp. gr.Pcca), Li₄Ge ₂ ^VI Ge ₇ ^VI O₂₀ (sp. gr. C2), and Li₂Ge^VIGe ₆ ^IV O₁₅ (sp. gr. Pbcn) has been made with the separation of subpolyhedral structural units (SPSUs) built by octahedra and tetrahedra. The topologically invariant SPSUs are separated in three-dimensional frameworks of the structures. A possible mechanism of the matrix assemblage from the SPSU invariants in crystal structures of the framework Li,Ge-germanates is suggested.     

Synthesis and crystal structure of new phosphate NaFe 4 2+ Fe 3 3+ [PO4]6

New sodium iron orthophosphate NaFe ₄ ²⁺ Fe ₃ ³⁺ [PO₄]₆ was synthesized by the hydrothermal method. The crystal structure (sp. gr. $P\bar 1$ ) was established by the heavy-atom method, with the exact chemical formula of the compound being unknown; R _hkl = 0.0492, R _whkl = 0.0544, S = 0.52. The new compound is analogous to iron phosphate Fe ₃ ²⁺ Fe ₄ ³⁺ [PO₄]₆ studied earlier. However, these two compounds differ in the Fe²⁺ and Fe³⁺ contents, because Na⁺ ions in the new compound are located at the centers of symmetry not occupied earlier.     

Cluster self-organization of TR,Ge-containing crystal-forming systems: Suprapolyhedral precursors and self-assembly of La3Ga[6]Ga 4 [4] Ge[4]O14 (langasite) and La3Ge[6]Ge 2 [5] Ge 2 [4] Ga[4]O16 gallogermanates

A combinatorial-topological analysis of the La₃Ga^[6]Ga ₄ ^[4] Ge^[4]O₁₄ and La₃Ge^[6]Ge ₂ ^[5] Ge ₂ ^[4] Ga^[4]O₁₆ gallogermanates, which have MT and MPT microporous frameworks composed of M octahedra (GeO₆, GaO₆), T tetrahedra (GeO₄, GaO₄), and P pyramids (GeO₅), is performed using the method of coordination sequences with the TOPOS 3.2 program package. It is established that the La₃Ga^[6]Ga ₄ ^[4] Ge^[4]O₁₄ gallogermanate is characterized by a crystal-forming net 6 6 6 (of the graphite type). A new type of the binodal net 6 10 1 0 + 6 10 (2: 1) is revealed in the La₃Ge^[6]Ge ₂ ^[5] Ge ₂ ^[4] Ga^[4]O₁₆ gallogermanate. The cyclic cluster precursors composed of six polyhedra with a lanthanum template atom at the center of the LaMT ₅ and LaMP ₃ T ₃ clusters are identified by the two-color decomposition of the nets in the structures of the La₃Ga^[6]Ga ₄ ^[4] Ge^[4]O₁₄ and La₃Ge^[6]Ge ₂ ^[5] Ge ₂ ^[4] Ga^[4]O₁₆ gallogermanates. The coordination numbers of the cluster precursors in these structures are found to be equal to 6 and 4 for two-dimensional nets and 8 and 6 for three-dimensional nets, respectively.     

Investigation into the growth and structure of thin-film solid solutions of iron-based superconductors in the FeSe0.92-FeSe0.5Te0.5 system

Thin films of FeSe_0.92 and FeSe_0.5Te_0.5 iron chalcogenide superconductors and solid solutions containing these components in different ratios have been grown on the surface of LaAlO₃ (10 $\bar 1$ 2) crystals by pulsed laser deposition. Films of solid solutions have been deposited by simultaneous laser ablation from two targets of the FeSe_0.92 and FeSe_0.5Te_0.5 stoichiometric compositions onto one substrate. An X-ray diffraction study of the film structure shows that the films grown are epitaxial and their lattice parameters regularly vary with the ratio of the deposited components, which was controllably varied by changing the ablation intensities from the targets.     

Crystal structure of new synthetic Ca,Na,Li-carbonate-borate

In the process of studying the phase formation in the Li₂CO₃-CaO-B₂O₃-NaCl system, new Ca,Na, Li-carbonate-borate has been synthesized under hydrothermal conditions. The crystal structure of carbonate-borate with the crystallochemical formula Ca₄(Ca_0.7Na_0.3)₃(Na_0.7□ _0.3)Li₅[B ₁₂ ^t B ₁₀ ^Δ O₃₆(O,OH)₆](CO₃)(OH) · (OH,H₂O) was refined to R _hkl = 0.0716 by the least squares method in the isotropic approximation of atomic thermal vibrations without the preliminary knowledge of the chemical composition and the formula (sp. gr. R3, a _rh = 13.05(2) Å, α = 40.32(7)]°, V = 838(2) ų, a _h = 8.99(2), c _h = 35.91(2) Å, V = 2513(2) ų, Z = 3, d _calcd = 2.62 g/cm³, Syntex P $\bar 1$ diffractometer, 3459 reflections, 2θ-θ method, λMo). The structure has a new boron-oxygen radical [B ₁₂ ^t B ₁₀ ^Δ O₃₆(O,OH)₆] _∞∞ ^15? , a double layer of nine-membered [B ₆ ^t B ₃ ^Δ O₁₅(O,OH)₃]^7.5?-rings bound by BO₃-triangles, and twelve-membered [B ₆ ^t B ₆ ^Δ O_19.5(O,OH)₃]^7.5? rings. This allows one to relate this compound to megaborates with complex boron-oxygen radicals. The structure is built from two types of blocks consisting of Ca,Na,B-and Li,B-polyhedra alternating along the c-axis, which explains the perfect cleavage of the crystals along the (0001) plane.     

Strain of interatomic bonds and crystallochemical aspects of AB 1 2/′ B 1 2/″ O3 oxides with perovskite structure

A method for determining the strain characteristics of interatomic bonds in crystals of ternary oxides AB ₁ ^2/′ B ₁ ^2/″ O₃ with perovskite structure, i.e., AB ₁ ^2/′ B ₁ ^2/″ O₃ (B″ = Nb, Ta, Sb, Re, or Bi) and AB ₁ ^2/′2+ B ₁ ^2/″6+ O₃ (B″ = Mo, W, Re, Os, or U), is developed. A linear relationship is established between the effective lengths of unstrained B-O bonds (l _0BO) and the lengths of unstrained B′-O (l _0B′O) and B″-O (l _0B″O) bonds, which differs from the Vegard rule. The found values of l _0B″O for ternary oxides with perovskite structure turned out to be close to the average interatomic B″-O distances in crystals of polymorphic phases of low-symmetry simple oxides. It is shown that the average length of the unstrained Pb-O bond in PbB ₁ ^2/′ B ₁ ^2/″ O₃ perovskites corresponds to the length of the same bond in binary oxides PbBO₃. For ternary oxides with perovskite structure, a linear correlation between the bond-strain energy and the temperature of their transition to the cubic phase is established. A linear correlation is found between the ratios of the Curie temperatures and the bond-strain energy for lead niobates and tantalates.     

Neutron refinement of the crystal structure of partially exchanged taurine, (ND 3 + )0.65(NH 3 + )0.35(CH2)2SO 3 −

Refinement of neutron-diffraction data from a partially deuteriated single crystal of taurine, 2-aminoethylsulfonic acid, confirms the zwitterion structure, ND ₃ ⁺ (CH₂)₂SO ₃ ^? , at room temperature; the S?C?C?N torsion angle of thegauche configuration in the solid state is ?69.4⁰. Hydrogen positions have been located more precisely than in the earlier X-ray analysis to yield apparent bond lengths N?D/H=1.02(1) Å and C?H=1.08(1) Å.     

X-Ray diffraction and IR-spectroscopic studies of UO2(n-C3H7COO)2(H2O)2 and Mg(H2O)6[UO2(n-C3H7COO)3]2

Single crystals of UO₂(n-C₃H₇COO)₂(H₂O)₂ (I) and Mg(H₂O)₆[UO₂(n-C₃H₇COO)₃]₂ (II) are synthesized. Their IR-spectroscopic and X-ray diffraction studies are performed. Crystals I are monoclinic, a = 9.8124(7) Å, b = 19.2394(14) Å, c = 12.9251(11) Å, β = 122.423(1)°, space group P2₁/c, Z = 6, and R = 0.0268. Crystals II are cubic, a = 15.6935(6) Å, space group $Pa\bar 3$ , Z = 4, and R = 0.0173. The main structural units of I and II are [UO₂(C₃H₇COO)₂(H₂O)₂] molecules and [UO₂(C₃H₇COO)₃]^? anionic complexes, respectively, which belong to AB ₂ ⁰¹ M ₂ ¹ (I) and AB ₃ ⁰¹ (II) crystal chemical groups of uranyl complexes (A = UO ₂ ²⁺ , B ⁰¹ = C₃H₇COO^?, and M ¹ = H₂O). A crystal chemical analysis of UO₂ L ₂ · nH₂O compounds, where L is a carboxylate ion, is performed.     

Dielectric and pyroelectric studies of an antiferroelectric liquid crystal

Polymorphism and polar properties of an antiferroelectric (R)-2-methylheptyloxycarbonylphenyl-4-[(4-decyloxy-3-fluoro)benzoyloxy]benzoate liquid crystal are studied. The phases are identified, and the phase transition points are determined. Dielectric constant, dielectric losses, and pyroelectric properties are studied for the orthogonal smectic SmA and tilted smectic, SmC _α ^* , SmC ^*, SmC _γ ^* , and SmC _A ^* phases. The temperature dependence of spontaneous polarization is measured by the repolarization current technique and integration of the pyroelectric constant.     

Synthesis and crystal structure of (CN3H6)2[UO2(OH)2(NCS)]NO3 and β-Cs3[UO2(NCS)5]

Compounds (CN₃H₆)₂[UO₂(OH)₂(NCS)]NO₃ (I) and β-Cs₃[UO₂(NCS)₅] (II) are synthesized and studied by IR spectroscopy and single-crystal X-ray diffraction. I and II crystallize in the orthorhombic system. For I, a = 12.2015(13) Å, b = 7.3295(8) Å, c = 16.310(2) Å, space group Pnma, Z = 4, and R = 0.0327; for II, a = 21.7891(6) Å, b = 13.5120(3) Å, c = 6.8522(2) Å, space group Pnma, Z = 4, and R = 0.0268. In structure I, complex groups form infinite chains [UO₂(OH)₂(NCS)] _n ^n? belonging to the AM ₂ ² M ¹ crystal chemical group of uranyl complexes (A = UO ₂ ²⁺ , M ² = OH^?, and M ¹ = NCS^?). The main structural elements of crystals II are mononuclear [UO₂(NCS)₅]^3? groups belonging to the AM ₅ ¹ group of uranyl complexes (A = UO ₂ ²⁺ and M ¹ = NCS^?). In I and II, uranium-containing complexes are connected with outer-sphere cations by electrostatic interactions, and in I a system of hydrogen bonds also contributes to their binding. Specific features of the packing of complex [UO₂(NCS)₅]^3? groups in the structures of two modifications of Cs₃[UO₂(NCS)₅] are discussed.     

Synthesis, properties, and crystal structure of barium 1-oxyethylidenediphosphonatohydroxogermanate(IV) polyhydrate Ba3[Ge(μ-OH)(μ-Oedph)]6 · 25H2O

The barium salt of 1-oxyethylidenediphosphonatohydroxogermanium acid Ba₃[Ge(μ-OH)(μ-Oedph)]₆ · 25H₂O (I) (H₄Oedph is 1-oxyethylidenediphosphonic acid) was synthesized and studied by X-ray diffraction. The complex was characterized by elemental analysis, thermogravimetry, and IR spectroscopy. The hexanuclear cyclic complex anions [Ge(μ-OH)(μ-Oedph)] ₆ ^6-t- ] cations, and water molecules of crystallization are the structural units of the crystal of I.     

Bimetallic hydrogen sulfates K4 M II[H(SO4)2]2(H2O)2 (M II = Mn or Zn)

Hydrogen sulfate hydrates K₄{M ^II[H(SO₄)₂]₂(H₂O)₂}, where M ^II = Mn or Zn, are synthesized, and their single-crystal structures are determined by X-ray diffraction. The structural units of the orthorhombic crystals (space group Pccn) are potassium and M ^II cations, SO ₄ ^2? and HSO ₄ ^? anions, and water molecules. Strong (2.52 Å) and moderate-in-strength (2.71–2.75 Å) hydrogen bonds link the anions and water molecules into hexamers. The M ^II cations, which have the octahedral environment (Mn-O, 2.14–2.19 Å and Zn-O, 2.07–2.11 Å), link the hexamers into flat layers. The structures of bimetallic hydrogen chalcogenate hydrates with different compositions are compared.     

Insertion of ethyl isothiocyanate into tungsten hexachloride: Crystal structure of ethyl-(4-ethyl-5-thioxo[1.2.4]dithiazolidin-3-ylidene)ammonium oxopentachlorotungstate(VI)

A product of the insertion of two isothiocyanate molecules into the same W-Cl bond, namely, W-Cl-WCl₅{N(Et)C(S)N(Et)C(S)Cl} (I), is synthesized by the reaction of WCl₆ with EtNCS in a dichloroethane solution. The hydrolysis of compound I results in the formation of single crystals of the complex . The structure of crystals II is determined using X-ray diffraction. It is demonstrated that structural units of crystals II are the [W^VIOCl₅]^? anionic complexes and the ethyl-(4-ethyl-5-thioxo[1.2.4]dithiazolidin-3-ylidene)ammonium cations.     

Preparation and analysis of multilayer composites based on polyelectrolyte complexes

A method for preparing multilayer film composites based on chitosan has been developed by the example of polymer pairs: chitosan–hyaluronic acid, chitosan–alginic acid, and chitosan–carrageenan. The structure of the composite films is characterized by X-ray diffractometry and scanning electron microscopy. It is shown that the deposition of a solution of hyaluronic acid, alginic acid, or carrageenan on a chitosan gel film leads to the formation of a polyelectrolyte complex layer at the interface, which is accompanied by the ordering of chitosan chains in the surface region; the microstructure of this layer depends on the nature of contacting polymer pairs.     

On the problem of transient hydrodynamic instability of nematics in magnetic field: I. Instability at splay deformation

A dependence of the square of dimensionless magnetic-field (MF) strength on the square of dimensionless wave vector of the domain structure, $h^2 \left( {\tilde q^2 } \right)$ , is analytically derived for the transient hydrodynamic instability arising at splay deformation under a MF. The domain formation is related to the fold catastrophe; the square of the critical field of domain formation, h _D ² , is determined from the condition ${{\partial \left[ {h^2 \left( {\tilde q^2 } \right)} \right]} \mathord{\left/ {\vphantom {{\partial \left[ {h^2 \left( {\tilde q^2 } \right)} \right]} \partial }} \right. \kern-0em} \partial }\left( {\tilde q^2 } \right) = 0$ . In the general case, the function $h^2 \left( {\tilde q^2 } \right)$ is a ratio of two polynomials whose coefficients for calamitics are determined by combinations of four dimensionless viscosities ν₂/ν₁, ν₆/ν₁, ν₇/ν₁, and ν₈/ν₁. Under some assumptions, the quotient of the polynomials at large $\tilde q^2$ is a quadratic function which allows one to experimentally determine the dimensionless viscosities ν₂/ν₁, ν₆/ν₁, ν₇/ν₁, and α₂/ν₁.     

Crystal structure of neptunium(V) sulfate hexahydrate, (NpO2)2SO4 · 6H2O

Single crystals of (NpO₂)₂SO₄ · 6H₂O are obtained, and their structure is determined. The structure is built of NpO ₂ ⁺ dioxo cations, SO ₄ ^2? anions, and molecules of coordination and crystallization water. The NpO ₂ ⁺ ions are linked into cationic ribbons stretched along the [001] direction. In the ribbons, neptunoyl ions of one type act as monodentate ligands, whereas neptunoyl ions of the other type coordinate the neighboring neptunoyl groups by two oxygen atoms. The Np(1) and Np(2) atoms have oxygen environments in the shape of a pentagonal bipyramid whose equatorial plane consists of oxygen atoms of the neighboring dioxo cations, sulfate ions, and water molecules. The sulfate ion acts as a bidentate ligand bridging the two neighboring atoms Np(1) and Np(2). Six water molecules are revealed in the structure; one of them is a crystallization water molecule. Hydrogen bonds link cationic ribbons into a three-dimensional network.