Self-propagating high-temperature synthesis of cubic niobium nitride under high pressures of nitrogen

Cubic niobium nitrides δ-NbN_x with different x = 0.87–1.015 were prepared by the self-propagating high-temperature synthesis (SHS) under nitrogen pressures of P(N₂) = 48–230 MPa.Nitrogen composition x as a function of P(N₂) was determined in weight gain experiments and compared with that determined by chemical (Kjeldahl) analysis. For powders with different x, the superconducting transition temperature T_c was measured as a function of lattice parameter a. The T_c values were found to grow linearly with increasing a. A maximum value of T_c = 15.0 K for cubic niobium nitride corresponded to a maximum value of a = 4.3901 Å.     

New biintercalation compounds in a potassiumcopper chloride-graphite system

Potassium interaction with stage 1 and stage 2 CuCl₂-graphite intercalation compounds (GICs) at T = 200°C was investigated. Two new phases with I_c = 14.70 Å and 12.55 Å were fixed. The analysis of the intensities of 001 reflections has shown that these two phases seem to be biintercalation compounds with the following sequences of the layers: K-CuCl-K-CuCl, respectively.     

Structure refinement of the as-synthesized and the calcined form of zeolite RUB-3 (RTE)

The structure analysis based on single crystal and powder data revealed that the framework structure of RUB-3 (structure type code RTE) consists of small [4⁴5⁴6²] building units and medium–large [4⁶5⁴6⁶8²] cages with a free volume of ca. 300 ų. Interconnected cages form a one-dimensional channel system with narrow, slightly elliptical pore openings (free diameter 3.6×4.3 Ų). ¹H–¹³C CP MAS NMR spectroscopy proved that the cages are occupied by disordered (±)-exo-2-aminobicyclo[2.2.1]heptane molecules which were used as templates during the synthesis. The unit cell composition of as-synthesized RUB-3 is (C₇H₁₃N)₂·[Si₂₄O₄₈]. The lattice parameters, bond lengths, bond angles and unit cell volumes are nearly identical for the as-synthesized [a=14.039(2) Å, b=13.602(2) Å, c=7.428(1) Å, β=102.22(3)°] and calcined form [a=14.018(1) Å, b=13.612(1) Å, c=7.418(1) Å, β=102.12(1)°] of RUB-3. The RTE structure even keeps its symmetry (C2/m) during the calcination process, indicating that the RTE framework topology is very rigid. All crystals are four-fold twins with twin planes {110}.     

A novel unexpected seven-coordinated chain-like dysprosium coordination polymer of pyridine-4-carboxylate: structure and photophysical property

One novel dysprosium coordination polymer [Dy(PIC)₃(H₂O)₂]_n (HPIC = pyridine-4-carboxylic acid) has been synthesized. X-ray analysis reveals that it forms the chain-like molecular structure through the bridged oxygen atoms of the carbonyl groups. The title coordination polymer crystallizes in the monoclinic system, space group C2/c, with lattice parameters: a=20.243(9) Å, b=11.576(5) Å, c=9.834(4) Å, β=110.601(2)°, V=2078(2) ų, D_c=1.805 mg/m³, Z=4, F(000)=1100, GOF = 1.11, R1=0.0404. The photophysical property has been studied with ultraviolet absorption spectrum, excitation and emission spectrum. The luminescence spectra show the stronger blue emission than yellow emission.     

Preparation, structure, and electrical conductivity of vanadium fluoridegraphite intercalation compound

Graphite intercalation compounds (GIC) of vanadium fluoride have been prepared in a fluorine atmosphere. The GICs prepared from highly oriented pyrolytic graphite (HOPG) were stage 1–8 compounds with composition, C_8.4–79.5VF_5.8–6.0. The apparent size of intercalated VF₆⁻(d_i) decreased from 5.33 Å to 4.15 Å along the c axis with increasing x in C_xVF₆. Various intercalated structures of VF₆⁻ between the carbon layers have been proposed for this change in d_i values. The compounds with small d_i around 4.2 Å show high stability in the air, which is due to the nestling of the VF₆⁻ anion between the carbon layers. Electron diffraction measurements have indicated that a well-nestled stage 2 GIC has high regularity in orientation of intercalated VF₆⁻ anions, which make two large unit cells of the hexagonal system ( ) with the different vectors by ±14° from that of graphite lattice. The ¹⁹F-NMR spectra and X-ray diffraction data in the low temperature region suggest a reversible phase transition. The highest electrical conductivity was 1.97 × 10⁵Scm⁻¹, which is 12 times that of pristine HOPG.     

[Zn(BDC)(H2O)2]n: a novel blue luminescent coordination polymer constructed from BDC-bridged 1-D chains via interchain hydrogen bonds (BDC = 1,4-benzenedicarboxylate)

A novel coordination polymer [Zn(BDC)(H₂O)₂]_n 1 (where BDC = 1,4-benzenedicarboxylate), has been synthesized and characterized by X-ray diffraction. 1 crystallizes in the monoclinic space group C2/c, a=15.09(2) Å, b=5.058(7) Å, c=12.196(16) Å, β=103.62(2)°, , Z=4. The most striking feature of 1 is that it consists of a high-dimensional network structure constructed from BDC-bridged 1-D chains via interchain hydrogen bonds. The coordination sphere of the zinc(II) ion is a distorted tetrahedron completed by four oxygen atoms from two water molecules and two BDC ligands. BDC adopts the bis-monodentated (syn–anti) coordination mode linking two adjacent zinc(II) ions. 1 shows strong blue photoluminescence as the result of the fluorescence from the intraligand emission excited state.     

Adsorption and intercalation of tetracycline by swelling clay minerals

Many of commonly used pharmaceuticals are hydrophilic. In aqueous solutions, these molecules will have strong interaction with swelling clay minerals, resulting in intercalation of these compounds in the interlayer of the minerals and retention by these minerals. In this research, we studied the intercalation of tetracycline (TC) into swelling clay minerals as represented by montmorillonite and rectorite of different surface charges and different charge densities. The maximum interlayer expansion was seen at a higher pH when the TC molecules adopted an extended conformation, even though, the amount of TC intercalated at higher pH is lower. Under pH 4–5, the intercalated TC produced an interlayer gallery height of 9.2 Å compared to 10.3 Å produced at pH 8.7 in the interlayer space of rectorite. Due to TC intercalation, the full width at half maximum (FWHM) becomes much broader, suggesting that the number of fundamental layers stacking along c axis decreased to 2–3. Depending upon the nature of the swelling clay minerals and the TC concentration, the intercalation process can be transitional, involving in the occurrence of mechanical mixtures, materials of intermediate layer thicknesses, and/or mixed layering of different ordering states.     

Electrochemical and surface properties of aluminium in citric acid solutions

The electrochemical and surface properties of aluminium in 0.05 M citric acid solutions of pH 2–8 were studied by means of open circuit potential (OCP), potentiodynamic polarization and potentiostatic current–time transient measurements. The OCP reached a steady-state value very slowly, probably due to the slow rate of detachment of surface complexes into the solution. Aluminium exhibits passive behaviour in citric acid solutions of pH 4–8. Tafel slopes b _c were characteristic for hydrogen evolution on aluminium covered by an oxide film. The corrosion kinetic parameters E _corr, i _corr and b _a suggest that surface processes are involved in the dissolution kinetics, especially in the pH range 3–6. Current–time transient measurements confirm that, in citric acid solutions of pH 3–6, the dissolution is controlled by surface processes, that is, by the rate of detachment of surface complexes, while in solutions of pH 2, 7 and 8 dissolution is under mass-transport control. The addition of fluoride ions to citric acid changes the controlling steps of the dissolution process. Citrate and fluoride ions compete for adsorption sites at the oxide surface, and adsorption of these ions is a competitive and reversible adsorption.     

A CdSO4-like 3-D framework constructed from monosodium substituted Keggin arsenotungstates and copper(II)-ethylenediamine complexes

A 6⁵·8 CdSO₄-like 3-D framework [Cu(en)₂]₃[α-AsW₁₁NaO₃₉]·2H₂O (1) constructed by monosodium-substituted Keggin arsenotungstates and copper(II)-ethylenediamine complexes (en = ethylenediamine) has been synthesized by reaction of Na₈[α-HAsW₉O₃₄]·11H₂O, CuCl₂·2H₂O and ethylenediamine under hydrothermal conditions and structurally characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis and single-crystal X-ray diffraction. Crystal data for 1: C₁₂H₅₂AsCu₃N₁₂NaO₄₁W₁₁, monoclinic, Cc, a = 20.409(9) Å, b = 16.737(8) Å, c = 16.561(7) Å, β = 104.607(7)°, V = 5474(4) Å³, T = 296(2) K; Z = 4, μ = 24.860 mm⁻¹, GOOF = 1.086, R₁ = 0.0284, wR₂ = 0.0759. To the best of our knowledge, 1 represents the first 6⁵·8 CdSO₄-like 3-D monovacant Keggin arsenotungstate derivative in polyoxometalate chemistry.     

Time-of-flight Rietveld neutron structure refinement and quantum chemistry study of Y-α-sialon

A Y-α-sialon was prepared using a specially designed temperature regime supporting formation of α-sialon and the amount of non-crystalline phase was remarkably reduced by a chemical treatment. Chemical composition of the sample was determined by EDX analysis. Crystal structure of Y-α-sialon was refined using high quality time-of-flight neutron powder diffraction data taken with the General Purpose Powder Diffractometer (GPPD) at the IPNS, Argonne National Laboratory. Unrestrained structure refinement was done in the P31c space group. The list of simultaneously refined parameters included profile parameters, atomic coordinates, individual isotropic temperature parameters and the occupancy parameter of Y. The contents of Y in the cell refined to 0.38(1) and calculated Si–N distances in tetrahedra varied from 1.716(3) to 1.773(3) Å, but their distributions in the respective tetrahedra differ as in the parent structure of α-Si₃N₄. Anisotropic temperature parameters refinement, as well as constrained refinements of the occupancy parameters of Si–Al and N–O pairs, were also attempted, but they all ended with unphysical values. Variation of the background was analyzed using RDF formalism. Three peaks centered around 1.7 Å (with a shoulder at 2.2 Å), 2.8 Å and 3.5 Å proved that the composition of amorphous phase was close to that of crystalline. Ab initio cluster calculations performed at the B3LYP/6-31G** level of theory excluded configuration with O atoms bonded to three Si atoms and proved that the most probable is the configuration where an O atom is shared by three Al atoms.     

Synthesis and structure of Mu-33, a new layered aluminophosphate

Mu-33, a new layered aluminophosphate with an Al/P ratio of 0.66, was obtained from a quasi non-aqueous synthesis in which tert-butylformamide (tBF) was the main solvent and only limited amounts of water were present. During the synthesis, tBF decomposed and the resulting protonated tert-butylamine is occluded in the as-synthesized material. The approximate structure was determined from data collected on a microcrystal (200 × 25 × 5 μm³) at the European Synchrotron Radiation Facility (ESRF) in Grenoble, but the quality of these data did not allow satisfactory refinement. Therefore the structure was refined using high-resolution powder diffraction data, also collected at the ESRF. The structure (P2₁/c, a = 9.8922(6) Å, b = 26.180(2) Å, c = 16.729(1) Å and β = 90.4(1)°) consists of anionic aluminophosphate layers that can be described as a six-ring honeycomb of alternating corner-sharing AlO₄ and PO₄ tetrahedra with additional P-atoms above and below the honeycomb layer bridging between Al-atoms. The tert-butylammonium ions and water molecules located in the interlayer spacing interact via hydrogen-bonds with the terminal oxygens of the P-atoms. The characterization of this new aluminophosphate by ¹³C, ³¹P, ¹H–³¹P heteronuclear correlation (HETCOR) and ²⁷Al 3QMAS solid state NMR spectroscopy is also reported.     

1,3,5-Triaza-7-phosphaadamantane (PTA) ligated iridium(I) complexes as catalysts for the intramolecular hydroamination of 4-pentyn-1-amine in water

The water-soluble complex [Ir(COD)(PTA)₃]Cl (1, PTA = 1,3,5-triaza-7-phosphaadamantane) was prepared by the reaction of [IrCl(COD)]₂ with six equivalents of PTA under a nitrogen atmosphere. Compound 1 was fully characterized in solution and the solid state. 1 crystallized in the monoclinic space group C2/c with a = 29.648(9) Å, b = 11.238(2) Å, c = 19.930(2) Å, and β = 96.55(2)°. Complex 1 and the related Ir(I) compounds, [IrCl(CO)(PTA)₃] (2) and [Ir(CO)(PTA)₄]Cl (3), were active catalysts in the intramolecular hydroamination of 4-pentyn-1-amine in water. This is the first reported study of the Ir(I) mediated transformation in aqueous media.     

An oxide chain constructed from octamolybdate, a Keggin anion and a copper (II) – Tetrapyridylpyrazine binuclear unit

The hydrothermal reaction of MoO₃, CuSO₄·5H₂O, tetra-4-pyridylpyrazine (tpyprz), and diphenyldiarsonic acid in water at 140 °C for 48 h yielded the one-dimensional material [{Cu₂(tpyprz)(H₂O)₃}₂{Mo₈O₂₆}{Mo₁₂O₃₆(AsO₄)}]·8H₂O (1·8H₂O). The chain structure of 1·8H₂O is constructed from alternating β-octamolybdate clusters and molybdoarsonate Keggin clusters linked through {Cu₂(tpyprz)(H₂O)₃}⁴⁺ binuclear subunits. The Cu(II) sites are inequivalent with one copper bonding to two pyridyl donors and a pyrazine nitrogen of one terminus of the tpyprz ligand, two aqua ligands and an oxo-group of the cluster while the second copper site coordinates to the nitrogen donors of the other terminus of the tpyprz ligand, an aqua group, a terminal oxo-group of the cluster and a terminal oxo-group of the mixed valence {Mo₁₁^VIMo^VO₃₆(AsO₄)}⁴⁻ cluster. Crystal data: C₄₈H₆₀AsCu₄Mo₂₀N₁₂O₈₀: FW = 4332.96 Triclinic , a = 12.5087(5) Å, b = 13.6681(6) Å, c = 14.8980(6) Å, α = 92.196(1)°, β = 97.046(1)°, γ = 97.751(1)°, Z = 1, D_calc = 2.877 g cm⁻³; structure solution and refinement based on 12,333 reflections (Mo K_α, λ = 0.71073 Å) converged at R₁ = 0.0540 and wR₂ = 0.1115.     

Structure of a methylamine sorption complex of fully dehydrated Cd-exchanged zeolite X, Cd46(CH3NH2)16[Si100Al92O384]-FAU

The structure of a methylamine sorption complex of fully dehydrated, fully Cd²⁺-exchanged zeolite X, Cd₄₆(CH₃NH₂)₁₆[Si₁₀₀Al₉₂O₃₈₄]-FAU (a = 24.863(4) Å), has been determined by single-crystal X-ray diffraction techniques in the cubic space group at 21(1) °C. An aqueous exchange solution 0.05 M in Cd²⁺ was allowed to flow past the crystal for 5 days. The crystal was then dehydrated at 480 °C and 2 × 10⁻⁶ Torr for 2 days (colorless), and exposed to 160 Torr of methylamine gas at 21(1) °C for 2 h (yellow). Diffraction data were then gathered in this atmosphere and were refined using all data to the final error indices (based upon the 524 reflections for which F_o > 4σ(F_o)) of R₁ = 0.069 and wR₂ = 0.200. In this structure, Cd²⁺ ions occupy three crystallographic sites. The octahedral sites I at the centers of the hexagonal prisms are filled with 16 Cd²⁺ ions per unit cell (Cd–O = 2.369(8) Å). The remaining 30 Cd²⁺ ions are located at two non-equivalent sites II with occupancies of 14 and 16. The 16 methylamine molecules per unit cell lie in the supercage where each interacts with one of the latter 16 site-II Cd²⁺ ions: N–Cd = 2.11(8) Å. The imprecisely determined N–C bond length, 1.49(22) Å, agrees with that in gaseous methylamine, 1.474 Å. The positions of the hydrogen atoms were calculated. It appears that one of the amino hydrogen atoms hydrogen bonds to a 6-ring oxygen, and that the other forms a bifurcated hydrogen bond to this and another 6-ring oxygen. The methyl group is not involved in hydrogen bonding.     

Uptake of cesium and strontium cations by potassium-depleted phlogopite

Phlogopite mica was equilibrated with 1.0 N sodium chloride (NaCl)–0.2 N sodium tetraphenylborate (NaTPB)–0.01 M disodium ethylenediaminetetraacetic acid (EDTA) solution at room temperature resulting in an almost complete removal (92%) of the mica's interlayer K. X-ray powder diffraction analysis provides additional evidence that hydrated Na⁺ ions had almost completely replaced the interlayer K⁺. Following equilibration, the c-axis spacing of the mica increased from 10.0 Å to approximately 12.2 Å. Cesium and Sr ion exchange isotherms indicate that K-depleted phlogopite is highly selective for both elements, the Cs⁺ exchange capacity is 1.26 meq/g or 65% of the theoretical cation exchange capacity and the Sr²⁺ exchange capacity is 1.94 meq/g or 100% of the theoretical exchange capacity of the mica. Kielland plots indicated that the mica was selective for Cs⁺ when the equivalent exchange capacity of Cs⁺ in the exchanger phase (X¯_Cs) was < 0.66 and selective for Sr²⁺ when X¯_Sr < 0.41. At equivalent fractions greater than these levels, layer collapse and/or steric effects limit the diffusion of these ions into the interlayers of the mica. Analysis of the Cs⁺ equilibrated mica utilizing XRD indicated that a collapse of the c-axis spacing had occurred. Based on the high selectivity of < 45-μm K-depleted phlogopite for Sr²⁺ and Cs⁺, this material may prove useful as an inorganic ion exchanger for these radioactive isotopes.     

Diaquabis(4,4-bipyridine)copper(II) di(o-sulfobenzimidate) dichloromethane solvate, a two-dimensional Cu4(4,4-C5H4NC5H4N)4 rhombic grid clathrating guest dichloromethane

In the crystal structure of bis(4,4^′-bipyridine)diaquacopper(II) di(o-sulfobenzimidate) dichloromethane solvate, the host polycationic [Cu(4,4^′-C₅H₄NC₅H₄N)₂(H₂O)₂]_∞ rhombic grids stack over each other 8.16 Å apart along the c-axis of the orthorhombic Pbcn unit cell. The Cu₄(4,4^′-bpy)₄ rhombus clathrating a disordered dichloromethane molecule has a copper atom at the corner and the spacer heterocycle with pyridyl rings twisted by 21.8(2)°, as its side. The anions occupy the space between the layers; the grids interact with each other indirectly through water–anion hydrogen bonds [OO=2.766(4); ]. The structure sets a remarkable example of potentials born by the polyfunctional o-sulfobenzimidate moiety for construction of unusual architectures.     

Crystal behavior of semicrystalline polystyrene‐block‐poly(l‐lactide) diblock copolymer in thin films with various structures

The crystal behavior of a semicrystalline polystyrene‐block‐poly(l ‐lactide) diblock copolymer in phase‐separated thin films with various thicknesses at different crystal temperatures has been investigated using atomic force microscopy and transmission electronic microscopy. Parallel and perpendicular lamellae could be obtained by annealing the thin films for different periods of time as reported previously (Chen et al., Macromolecules 40:6631 (2007)). At different temperatures, crystallization in thin films with parallel lamellar structure in the melt state gives dendrite crystals with orthorhombic structure, and the ordered structure in the melt is destroyed after crystallization. When crystallization occurs in thin films with perpendicular lamellar structure, crystal morphology and structure are greatly affected by the crystallization temperature (T_c). When T_c < T_g,ps, where T_g,ps is the glass transition temperature of a polystyrene block, crystallization is hardly confined within the lamellae. The morphology is preserved but the long period of the perpendicular lamellae is increased after crystallization. When T_c > T_g,ps, rod‐like crystals dominate the final morphology, and crystallinity destroys completely the structure in the melt.© 2012 Society of Chemical Industry     

A hemidirected 1-D coordination polymer [Pb2(H2O)2(HBTC)2] · 3H2O extended in holodirected 3-D by weak Pb–O interactions

A new complex, [Pb₂(H₂O)₂(HBTC)₂] · 3H₂O (H₃BTC = 1,3,5-Benzenetricarboxylic acid) (1), has been synthesized under hydrothermal condition. The single-crystal analysis shows that 1 consists of 1-D double-chains with Pb(II) six-coordinated by three H₃BTC and one H₂O molecule with the Pb–O bond distances in the range of 2.56–2.76 Å. When the Pb–O bonding limit extends from 2.76 to 2.90 Å, the potential weak bonds of Pb–O can be found and the coordination number of Pb will increase from six to nine. As a result, the coordination geometry of Pb(II) transforms from hemidirected to holodirected and an infinite 3-D framework is obtained by the connection of the double-chains. The IR spectrum and the TGA–DTA curve of 1 are also reported in this paper.     

The hydrothermal synthesis and structure of a one-dimensional Fe(II)molybdophosphate

A new one-dimensional Fe(II)molybdophosphate of the formula, [(C₁₀H₈N₂)H₂]₂[Fe₄^(II)Mo₁₂^(V)(HPO₄)₆(PO₄)₂(H₂O)₈(OH)₆O₂₄]·8H₂O, (1), has been synthesized by employing hydrothermal methods and characterized by single crystal X-ray diffraction. The structure consists of a network of MO₆ (M = Fe, Mo) octahedra and (H)PO₄ tetrahedra linked through their vertices. The connectivity between the polyhedral units gives rise to one-dimensional chains with eight-membered apertures. The hydrogen bonded interactions between the chains form pseudo two-dimensional layers. Extensive hydrogen bonding also exists between the amine molecule, 4,4^′-bipyridine, water molecule and framework oxygen atoms. Crystal data for 1: monoclinic, space group = P2₁ (no. 4), a=12.549(3) (Å), b=23.496(5) (Å), c=14.551(3) (Å), β=114.87(3)°, , and Z=2.     

Homogeneous crystalline FeSi2 films of c (4?×?8) phase grown on Si (111) by reactive deposition epitaxy

The growth of iron silicides on Si (111) using reactive deposition epitaxy method was studied by scanning tunneling microscopy and X-ray photoelectron spectroscopy (XPS). Instead of the mixture of different silicide phases, a homogeneous crystalline film of c (4 × 8) phase was formed on the Si (111) surface at approximately 750°C. Scanning tunneling spectra show that the film exhibits a semiconducting character with a band gap of approximately 0.85 eV. Compared with elemental Fe, the Fe 2p peaks of the film exhibit a lower spin-orbit splitting (−0.3 eV) and the Fe 2p_3/2 level has a smaller full-width at half maximum (−0.6 eV) and a higher binding energy (+0.3 eV). Quantitative XPS analysis shows that the c (4 × 8) phase is in the FeSi₂ stoichiometry regime. The c (4 × 8) pattern could result from the ordered arrangement of defects of Fe vacancies in the buried Fe layers.