Adjacent Octahedra Research Articles

Natural speciation of Ni, Zn, Ba, and As in ferromanganese coatings on quartz using X-ray fluorescence, absorption, and diffraction

The mineralogy of natural ferromanganese coatings on quartz grains and the crystal chemistry of associated trace elements Ni, Zn, Ba, and As were characterized by X-ray microfluorescence, X-ray diffraction, and EXAFS spectroscopy. Fe is speciated as ferrihydrite and Mn as vernadite. The two oxides form alternating Fe- and Mn-rich layers that are irregularly distributed and not always continuous. Unlike naturally abundant Fe–vernadite, in which Fe and Mn are mixed at the nanoscale, the ferrihydrite and vernadite are physically segregated and the trace elements clearly partitioned at the microscopic scale. Vernadite consists of two populations of interstratified one-water layer (7 Å phyllomanganate) and two-water layer (10 Å phyllomanganate) crystallites. In one population, 7 Å layers dominate, and in the other 10 Å layers dominate. The three trace metals Ni, Zn, and Ba are associated with vernadite and the metalloid As with ferrihydrite. In vernadite, nickel is both substituted isomorphically for Mn in the manganese layer and sorbed at vacant Mn layer sites in the interlayer. The partitioning of Ni is pH-dependent, with a strong preference for the first site at circumneutral pH and for the second at acidic pH. Thus, the site occupancy of Ni in vernadite may be an indicator of marine vs. continental origin, and in the latter, of the acidity of streams, lakes, or soil pore waters in which the vernadite formed. Zinc is sorbed only in the interlayer at vacant Mn layer sites. It is fully tetrahedral at a Zn/Mn molar ratio of 0.0138, and partly octahedral at a Zn/Mn ratio of 0.1036 consistent with experimental studies showing that the VIZn/ IVZn ratio increases with Zn loading. Barium is sorbed in a slightly offset position above empty tetrahedral cavities in the interlayer. Arsenic tetrahedra are retained at the ferrihydrite surface by a bidentate-binuclear attachment to two adjacent iron octahedra, as commonly observed. Trace elements in ferromanganese precipitates are partitioned at a few, well-defined, crystallographic sites that have some elemental specificity, and thus selectivity. The relative diversity of sorption sites contrasts with the simplicity of the layer structure of vernadite, in which charge deficit arises only from Mn 4+ vacancies (i.e., no Mn 3+ for Mn 4+ substitution). Therefore, sorption mechanisms primarily depend on physical and chemical properties of the sorbate and competition with other ions in solution, such as protons at low pH for Ni sorption.

Compositional and structural control on anion sorption capability of layered double hydroxides (LDHs)

Layered double hydroxides (LDHs) have shown great promise as anion getters. In this paper, we demonstrate that the sorption capability of a LDH for a specific oxyanion can be greatly increased by appropriately manipulating material composition and structure. We have synthesized a large set of LDH materials with various combinations of metal cations, interlayer anions, and molar ratios of divalent cation M(II) to trivalent cation M(III). The synthesized materials have then been tested systematically for their sorption capabilities for pertechnetate (TcO − 4). It is discovered that for a given interlayer anion (either CO 2− 3 or NO − 3) the Ni–Al LDH with a Ni/Al ratio of 3:1 exhibits the highest sorption capability among all the materials tested. The sorption of TcO − 4 on M(II)–M(III)–CO 3 LDHs may be dominated by the edge sites of LDH layers and correlated with the basal spacing d 003 of the materials, which increases with the decreasing radii of both divalent and trivalent cations. The sorption reaches its maximum when the layer spacing is just large enough for a pertechnetate anion to fit into a cage space among three adjacent octahedra of metal hydroxides at the edge. Furthermore, the sorption is found to increase with the crystallinity of the materials. For a given combination of metal cations and an interlayer anion, the best crystalline LDH material is obtained generally with a M(II)/M(III) ratio of 3:1. Synthesis with readily exchangeable nitrate as an interlayer anion greatly increases the sorption capability of a LDH material for pertechnetate. The work reported here will help to establish a general structure–property relationship for the related layered materials.

Relation between x-ray emission mechanism and crystal structure in LiNbO3

x-ray emission in LiNbO3 is confirmed by thermal treatments in a vacuum system by a new cleaning method of the crystal. Detailed single-crystal high-temperature x-ray structure refinements were carried out at 297, 323, 373, 423 and 473 K, far below the phase transition (∼1473 K). The unit cell dimensions a and V show a linear increase with temperature; however, the lattice parameter, c shows only a slight linear increase. The length of Nb–O bonds in adjacent octahedra is almost constant below 423 K. It is suggested that the valence electron in Nb changes in the compound. Therefore, x-ray emission induced by charged particles including electrons can be considered to have a close relation to the electric charge of Nb in LiNbO3.

Hydrothermal synthesis and characterization of the first 1-D indiumphosphate chain In 2(HPO 4) 2(H 2PO 4) 2F 2·C 4N 2H 12, a precursor for high dimensional structures

The first one-dimensional (1-D) indiumphosphate chain, In 2(HPO 4) 2(H 2PO 4) 2F 2·C 4N 2H 12 ( 1), has been hydrothermally prepared using piperazine (PIP) as a template. The structure consists of infinite chains of trans, trans-corners-sharing InO 4F 2 octahedra with the adjacent octahedra being bridged by tetrahedral PO 3(OH) and PO 2(OH) 2 units, which are H-bonded with amine groups of the organic cations. Interestingly, this macroanionic chain InP 2O 8H 3F − is similar to that found in the mineral tancoite-like chains and has potential to further set up higher-dimensional networks. On heating 1 in the presence of additional phosphoric acid at 180 °C under hydrothermal condition, compound 2, In 2(OH)(H 2O)(PO 4) 2·H 3O·H 2O, possessed a 3-D structure building from the repetition of a secondary building unit is obtained. When 1 is heated with additional PIP, an unknown phase, compound 3 is formed. Finally, on treatment with another amine, such as diethylenetriamine or 1,4-diaminobutane, at 180 °C, 1, as a precursor, can convert into a previously known 3-D framework structure with 16-membered ring compound 4. Compounds 1 and 2 are determined by single-crystal X-ray diffraction. Furthermore, 1 is characterized by X-ray powder diffraction, IR spectroscopy, inductively coupled plasma analysis, thermogravimetric analysis and differential thermal analysis.

The crystal structure of Cu1.78Bi4.73Se8, an N = 3 pavonite homologue with a Cu-for-Bi substitution

Summary Cu1.78Bi4.73Se8, synthesized in a dry phase system Cu—Bi—Se at 450 °C, is monoclinic, a = 13.759 Å, b = 4.168 Å, c = 14.683 Å, γ = 115.61°, space group C2/m. It is an N = 3 member of the pavonite homologous series, with the composition limits Cu1.96Bi4.67Se8—Cu1.77Bi4.60S8—Cu1.25Bi4.91Se8. The crystal structure is composed of two types of alternating slabs, with configurations typical for the above series. The first kind of slabs contains paired square pyramidal columns of Bi3, interconnected by octahedral columns with three distinct statistical copper sites (flattened tetrahedral sites in the octahedral interior and a tetrahedral site between adjacent octahedra). They add up to nearly 1.5 Cu. The second kind of slabs contains central octahedra of Bi1, flanked by marginal distorted octahedra of Bi2. These Bi sites are partly replaced by statistically occupied Cu1-3 sites, in flat-tetrahedral and irregular trigonal-planar coordinations. Details of the Cu-for-Bi substitutions are discussed and comparisons with other N = 3 homologues of pavonite are made in the paper.

Synthesis and Characterization of [PtIn6](GeO4)2O and Its Solid Solution [PtIn6](GaO4)2-x(GeO4)xOx/2 (0 ≤ x ≤ 2): Gradual Color Change of the Solid Solution from Black (x = 0) to Yellow (x = 2) as a Consequence of Quantum Dot Effect

A new phase [PtIn6](GeO4)2O, a filled variant of [PtIn6](GaO4)2, and the solid solution [PtIn6](GaO4)(2-x)(GeO4)xOx/2 (0 < or = x < or = 2) were prepared and characterized. Single-crystal structure refinements show that [PtIn6](GeO4)2O is isotypic with the mineral, sulfohalite Na6FCl(SO4)2, and crystallizes in the space group Fmm (Z = 4) with a = 1006.0(1) pm. The building units of [PtIn6](GeO4)2O are isolated [PtIn6]10+ octahedra and (GeO4)4- tetrahedra, and the isolated O2- ions occupy the centers of the In6 octahedra made up of six adjacent PtIn6 octahedra. The lattice parameter of the solid solution [PtIn6](GaO4)(2-x)(GeO4)xOx/2 (0 < or = x < or = 2) varies gradually from a = 1001.3(1) pm at x = 0 to a = 1006.0(1) pm at x = 2, and the color of the solid solution changes gradually from black (x = 0) to red (x = 1) to yellow (x = 2). The cause for the gradual color change was examined by performing density functional theory electronic structure calculations for the end members [PtIn6](GaO4)2 and [PtIn6](GeO4)2O. Our analysis indicates that an oxygen atom at the center of a In6 octahedron cuts the In 5p/In 5p bonding interactions between adjacent [PtIn6]10+ octahedra thereby raising the bottom of the conduction bands, and the resulting quantum dot effect is responsible for the color change.

First-principles study of protonic conduction in In-doped AZrO 3 ( A=Ca, Sr, Ba)

The first-principles calculations based on the density functional theory were carried out to investigate the effects of A-cations on the protonic conductivity of AZrO 3 ( A=Ca, Sr, Ba). The local geometries around proton and dopant ion, formation energies of interstitial proton and activation energies for proton transfer were simulated in the In-doped CaZrO 3, SrZrO 3 and BaZrO 3. The results showed that the crystallographic feature of AZrO 3 ( A=Ca, Sr, Ba) is an important factor to control the protonic conduction. In the In-doped CaZrO 3 or SrZrO 3 with the orthorhombic structure, there is a unique stabilized proton site located between two adjacent octahedra. But in the In-doped BaZrO 3 with the cubic structure, there exists a certain region of stable sites between them. As the ionic radii of A-cations decrease, the crystal symmetry changes from cubic to orthorhombic, resulting in the rotation of ZrO 6 (or InO 6) octahedra, which causes the increase of activation energies for proton transfer in the oxides.

The accurate crystal chemistry of ferric smectites from the lateritic nickel ore of Murrin Murrin (Western Australia). II. Spectroscopic (IR and EXAFS) approaches

AbstractFe-rich smectites from lateritic weathering profiles have previously been studied by XRD, ICP-AES, SEM-EDX and TEM-EDX analyses (Gaudinet al., 2004). These smectites exhibit intermediate chemistries between five end-members: Al-Fe beidellites, Al-Fe montmorillonites and Mg+Ni-saponite. The spectroscopic study by FTIR and XAS of these smectites reveals that: (1) tetrahedral Fe3+is near or below the detection limit (0.05 cation for 4Si); (2) the large chemical variability is due to substitution of the three major cations (Fe, Al, Mg) within adjacent octahedra; (3) Ni is not concentrated in another clay phase such as Ni-kerolite and is located in the octahedral sheets of smectite; (4) octahedral cations are not randomly distributed but ordered in separated Fe, Al, Mg, Ni clusters; (5) the Mg-Ni saponite end-member actually appears as small trioctahedral clusters of Mg and Ni distributed within the dioctahedral smectite.

Thermal stability and structural deformation of rutile SnO 2 nanoparticles

Nanoparticles of rutile SnO 2 were synthesized by precipitation at room temperature. Samples were characterized with X-ray diffraction, transmission electron microscopy, thermoanalysis and nitrogen physisorption by BET method. The rutile crystalline structure was refined by Rietveld method. Crystallites had spherical morphology with crystallite sizes growing with the annealing temperature. The spherical crystallites aggregate to form grains composed of a number of crystallites defining the specific surface area and porosity. The crystallites contained hydroxyls in their structure and on their surface generating considerable amount of tin vacancy sites in the structure. These hydroxyls modify the Sn–O bonds, increase the lattice parameters and produce asymmetry in the representative rutile tin–oxygen octahedron. As the dehydroxylation was done with the annealing temperature, the atomic bond length between the oxygen atoms shared by adjacent octahedra decreased, contracting the lattice and increasing the symmetry.

High‐Temperature Lithium Mobility in α‐LiZr2(PO4)3 NASICON by Neutron Diffraction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

High-Temperature Lithium Mobility in α-LiZr2(PO4)3 NASICON by Neutron Diffraction

Powder neutron diffraction data at high resolution (HRPD instrument, ISIS Facility, U.K.) were collected on the lithium ion conductor α-LiZr2(PO4)3 at 673 K (a = 8.84448(3) Å, c = 22.2875(1) Å), and 873 K (a = 8.83667(4) Å, c = 22.4177(2) Å). Previous data measured at 423 K were included in the analysis. By Fourier maps and Rietveld refinement of the rhombohedral R3̄c crystal structure, it was shown that most lithium occupies the 6-fold disordered primary Li1 site, located off the symmetry center, at all temperatures. However, a 3-fold disordered secondary Li2 site was discovered, between two adjacent ZrO6 octahedra along the z axis, where a minor part of lithium is located. The fraction of lithium on Li2 increases with temperature from 10% (423 K) to 22% (873 K), and this may affect the mechanism of Li+ ion mobility. Li2 was not taken into account in the previous analysis of the 423 K data. Small but significant configurational changes of the Li1 and Li2 coordination environments occur between 423 and 873 K, which can account for the second-order phase transformation suggested in the literature to occur in the range 553 to 623 K on the basis of NMR and electrical conductivity data.

Crystallography and crystallite morphology of rutile synthesized at low temperature

Rutile was prepared at low temperature with titanium trichloride in an acid- and oxygen-rich environment. Samples were characterized with X-ray powder diffraction, transmission electron microscopy, and thermogravimetry; rutile's crystalline structure was refined with the Rietveld method. Crystallites were needles with their largest dimension along c lattice parameter; they grew in bundles parallel to their length axis, and contained hydroxyls in their lattice and on their surface. When samples were annealed, dehydroxylation generated lattice defects that produced microstrains and created conditions for crystallite sintering at temperatures above 300°C. Titanium–oxygen interaction in rutile depended on the annealing temperature, which gave rise to changes in the symmetry of the representative rutile titanium–oxygen octahedron. The atomic bond length between the oxygen atoms shared by adjacent octahedra decreased with the temperature, contracting the lattice. All this was caused by the variation of the number of hydroxyls in the lattice.

ELUSIVE BINARY NITRIDE PREPARED

SODIUM NITRIDE, A COMpound that some scientists claimed could not exist, has been prepared and characterized by chemists at the Max Planck Institute for Solid-State Research, Stuttgart, Germany Research chemist Dieter Fischer and chemistry professor Martin Jansen prepared amorphous solid Na 3 N by generating atomic beams of sodium and nitrogen separately in a vacuum chamber and codepositing the atoms onto a liquid-nitrogencooled sapphire substrate [ Angew. Chem. Int. Ed., 41, 1755 (2002)]. The Na 3 N changes to a crystalline form when heated to room temperature and decomposes into its elements at 87 °C. Analysis of X-ray powder diffraction patterns of the crystals reveals that the compound has a lattice structure of the type known as anti-Re0 3 in which octahedra are connected at all six corners to adjacent octahedra to form a three-dimensional network. Six sodium cations are located at the corners and one nitrogen atom is in the center of each octahedron. Sodium nitride is an extremely labile ...

Hydrothermal synthesis and crystal structure of two novel aluminophosphites containing infinite Al–O–Al chainsElectronic supplementary information (ESI) available: XRD patterns and views of NKX-1 and NKX-4. See http://www.rsc.org/suppdata/jm/b2/b200507g/

Two novel aluminophosphites, [NH2(CH2)6NH2][Al(OH)(H(HPO3))2] and [Al(OH)(H(HPO3))2]·2H2O (denoted as NKX-1 and NKX-4, respectively), with a molar ratio P∶Al = 2, have been synthesized for the first time using a hydrothermal technique. Single crystals of these compounds have also been prepared. Structure refinement from single crystal X-ray diffraction data shows NKX-1 with composition [NH2(CH2)6NH2][Al(OH)(H(HPO3))2] crystallizes in the monolinic space group C2/c, with a = 29.123(17) Å, b = 6.772(4) Å, c = 6.851(4) Å, V = 1349.3(14) Å3, Z = 4, and NKX-4 with composition [Al(OH)(H(HPO3))2]·2H2O crystallizes in the orthorhombic space group Cmma, with a = 6.949(2) Å, b = 17.398(6) Å and c = 7.903(3) Å, V = 955.4(6) Å3, Z = 4. Both compounds contain AlO6 octahedra and HPO2 (OH) tetrahedra in their structure. Each AlO6 octahedron shares two hydroxide group corners with two adjacent AlO6 octahedra to form infinite Al–O–Al chains.

Contrasting Structural Behavior in the Aurivillius Phase Ferroelectrics Bi4Ti3O12, BaBi4Ti4O15 and Ba2Bi4Ti5O18

ABSTRACTThe crystal structures of the Aurivillius phase ferroelectrics Bi4Ti3O12, BaBi4Ti4O15 and Ba2Bi4Ti5O18, containing perovskite-like layers consisting of three, four and five adjacent TiO6 octahedra, respectively, have been analysed using high-resolution powder neutron diffraction data. At 2K the structure of Bi4Ti3O12 can be successfully modelled in the orthorhombic space group B2cb, with no evidence of the monoclinic distortion in the ferroelectric phase suggested by previous single crystal studies. At 298K BaBi4Ti4O15 shows a subtle orthorhombic distortion, but without the octahedral tilting seen in related ferroelectric phases, and is refined in space group F2mm. At 298 K Ba2Bi4Ti5O18 adopts a tetragonal polar phase (I4mm), thus displaying a third type of polar distortion within this family. It is suggested that these differences arise from a ‘tolerance factor’ type mechanism whereby the increasing content of the large Ba2+ cation causes a shift from underbonding at the perovskite A-site to underbonding at the perovskite B-site resulting in a change in the mechanism of ferroelectricity from A-site displacements to B-site displacements, akin to the mechanism in BaTiO3.

The structure of three cadmium hexacyanometallates(II): Cd2[Fe(CN)6]·8H2O, Cd2[Ru(CN)6]·8H2O and Cd2[Os(CN)6]·8H2O

Cd2[MII(CN)6]·8H2O, where M=Fe, Ru and Os, form a family of isomorphous compounds which crystallize in the monoclinic P21/n space group. MII cations present their usual octahedral coordination, while the cadmium atom coordinates to three nitrogen atoms from the cyanide groups and three water molecules forming a distorted octahedron. The rest of the water molecules are located in small channels in the structure and are hydrogen bonded to the coordinated ones. Adjacent cadmium octahedra share one edge to form the moiety: Cd2N6(H2O)4, in such a way that two metal sequences are observed: MII–Cd–MII and MII–Cd–Cd–MII, forming a tridimensional network. Coordinated and zeolitic water molecules can be removed preserving the M–CN–Cd framework.

ChemInform Abstract: Li2Sn(OH)6.

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Systematic ab initio study of the compressibility of silicate garnets.

The structural properties of the silicate garnets andradite, Ca(3)Fe(2)Si(3)O(12), uvarovite, Ca(3)Cr(2)Si(3)O(12), knorringite, Mg(3)Cr(2)Si(3)O(12), goldmanite, Ca(3)V(2)Si(3)O(12), blythite, Mn(2+)(3)Mn(3+)(2)Si(3)O(12), skiagite, Fe(2+)(3)Fe(3+)(2)Si(3)O(12), calderite, Mn(2+)(3)Fe(3+)(2)Si(3)O(12), and khoharite, Mg(3)Fe(3+)(2)Si(3)O(12), have been investigated with a quantum-mechanical model as a function of applied pressure. The study has been performed with the density functional theory code CASTEP, which uses pseudopotentials and a plane-wave basis set. All structural parameters have been optimized. The calculated static geometries (cell parameters, internal coordinates of atoms and bond lengths), bulk moduli and their pressure derivatives are in good agreement with the experimental data available. Predictions are made for those cases where no experimental data have been reported. The data clearly indicate that the elastic properties of all silicate garnets are dominated by the compressibility of the dodecahedral site. The compression mechanism is found to be based on a bending of the angle between the centers of the SiO(4) tetrahedra and the adjacent octahedra, as in the aluminosilicate garnets. An analysis of the relationship between ionic radii of the cations and the compressibility of silicate garnets is presented.

Solvothermal Synthesis and Structure of Ni(HP2O7)F·C2N2H10, a New Fluorinated Nickel Phosphate with a Chain Structure

A new one-dimensional fluorinated nickel phosphate Ni (HP2O7)F·C2N2H10 has been synthesized solvothermally using ethylenediamine as the template and its structure was determined by means of single-crystal X-ray diffraction. The title compound crystallizes in the monoclinic system, space group C/2c (No. 15) with M=314.78, a=12.658(3) Å, b=14.502 (3) Å, c=10.820(3) Å, β=109.924(5)°, V=1867.3(8) Å3, Z=8, R=0.0318, and wR=0.0670. The structure consists of infinite chains of cis, trans-corner-sharing NiO4F2 octahedra with the adjacent octahedra being bridged by HP2O7 groups, which are H-bonded with amine groups of the organic cations. The Ni–F bond lengths along the backbone of the chain are alternately short and long. The as-synthesized product is characterized by powder X-ray diffraction, IR spectroscopy, inductive couple plasma analysis, thermogravimetric analysis, and differential thermal analysis.

Li2Sn(OH)6

Hydrothermally prepared dilithium tin hexahydroxide crystallizes in the monoclinic system (space group P2(1)/n), with the Sn atom at a site with -1 symmetry and all other atoms in general positions. The Sn coordination polyhedron is made up of six hydroxide groups. The Li atom is tetrahedrally coordinated by oxygen, with the tetrahedra sharing two corners and one edge with the adjacent Sn octahedra. Hydrogen bonds between the OH groups provide additional bonds in the framework.