O4 Tetrahedra Research Articles

Crystal structure of holtite I

The crystal structure of As-containing holtite I is refined (Ital Structures diffractometer, 939 crystallographically independent reflections, anisotropic approximation, R = 0.047). The parameters of the orthorhombic unit cell are a = 4.695(1) A, b = 11.906(3) A, c = 20.38(3) A, sp. gr. Pnma, Z = 4. On the whole, the structural formula obtained, (Si2.43Sb0.36As0.21)BO3[(Al0.62Ta0.26□)Al2(Al0.98□)2(Al0.94□)2O12](O,OH,□)2.65, corresponds to the electron-probe analysis data. The statistical replacement of (Si,As)O4 tetrahedra by pyramidal [SbO3] groups is confirmed. The X-ray diffraction spectra of holtite I are compared with those of holtite II.

Confirmation of the Semivacant Wells−Dawson Polyoxotungstate Skeleton. The Structures of [Ce{X(H4)W17O61}2]19- (X = P, As) Indicate the Probable Location of Internal Protons

Reaction of Ce(III) with lacunary versions of [H(4)XW(18)O(62)](7-) (X = P, As) yields the 1:2 complexes [Ce(H(4)XW(17)O(61)](19-) (X = As, 1; P, 2) in good yield, characterized in solution and the solid state by NMR spectroscopy and X-ray crystallographic analysis, respectively. The structures confirm a syn C(2) conformation that is analogous to that observed for [Ln(alpha(2)-P(2)W(17)O(61))(2)](17-) but with "empty" O(4) tetrahedra that are in positions remote from the cerium atom. Bond valence sum calculations for these structures show that the four protons that are required for charge balance in all salts of the XW(18) anions and their lacunary derivatives are almost certainly bound to the oxygen atoms of the empty tetrahedra.

Thermal Transformation of (NH4)[Fe(AsO4)F] Into the New Textural Porous Orthorhombic Fe(AsO4) Phase. Crystal Structures, Thermal Behavior, and Spectroscopic and Magnetic Properties

(NH4)[Fe(AsO4)F] 1 has been synthesized under mild hydrothermal conditions. Single crystals of this phase heated under air atmosphere at 525 °C in a tubular furnace gave single crystals of the new polymorphous Fe(AsO4) 2. The crystal structure of both compounds has been determined from X-ray single-crystal diffraction data. Compound 1 crystallizes in the orthorhombic Pna21 space group with unit-cell parameters of a = 13.270(2) A, b = 6.629(1) A, c = 10.866(1) A, V = 955.8(2) A3, and Z = 8. Compound 2 belongs to the orthorhombic space group Imam, the unit cell parameters are a = 13.468(2) A, b = 6.525(1) A, c = 10.768(2) A, V = 946.3(3) A3, and Z = 12. The crystal structure of compound 1 consists of a three-dimensional framework with chains formed by alternating Fe(2)O4F2 or Fe(1)O4F2 octahedra and As(2)O4 or As(1)O4 tetrahedra, respectively, linked by a common oxygen vertex. These chains run along the a and b axes of the crystal structure. The crystal structure of 2 is formed by a three-dimensional skelet...

A novel open-framework with non-crossing channels in the uranyl vanadates A(UO2)4(VO4)3 (A=Li, Na)

A new sodium uranyl vanadate Na(UO2)4(VO4)3 has been synthesized by solid-state reaction and its structure determined from single-crystal X-ray diffraction data. It crystallizes in the tetragonal symmetry with space group I41/amd and following cell parameters: a=7.2267(4) Å and c=34.079(4) Å, V=1779.8(2) Å3, Z=4 with ρmes=5.36(3) g/cm3 and ρcal=5.40(2) g/cm3. A full-matrix least-squares refinement on the basis of F2 yielded R1=0.028 and wR2=0.056 for 52 parameters with 474 independent reflections with I⩾2σ(I) collected on a BRUKER AXS diffractometer with MoKα radiation and a CCD detector. The crystal structure is characterized by ∞2[(UO2)2(VO4)] sheets parallel to (001) formed by corner-shared UO6 distorted octahedra and V(2)O4 tetrahedra, connected by V(1)O4 tetrahedra to ∞1[UO5]4− chains of edge-shared UO7 pentagonal bipyramids alternately parallel to the a- and b-axis. The resulting three-dimensional framework creates mono-dimensional channels running down the a- and b-axis formed by face-shared oxygen octahedra half occupied by Na. The powder of Li analog compound Li(UO2)4(VO4)3 has been synthesized by solid-state reaction. The two compounds exhibit high mobility of the alkaline ions within the two-dimensional network of non-intersecting channels.

Synthesis, Crystal Structure and Characterization of New 12H Hexagonal Perovskite‐Related Oxides Ba6M2Na2X2O17 (M: Ru, Nb, Ta, Sb; X: V, Cr, Mn, P, As)

AbstractFor Abstract see ChemInform Abstract in Full Text.

Raman scattering study of Tb(V1−xPx)O4 single crystals

The polarized Raman spectra of a series of isostructural vanadate/phosphate compounds of the form: Tb(V1−xPx)O4 with 0⩽x⩽0.75 have been investigated at room temperature. While the observed Raman spectra are generally consistent with group theory predictions for a body-centered tetragonal crystal structure (D4h19), due to the replacement of P for V, additional spectral features induced by the disorder of the mixed vanadate/phosphate system are also observed. In particular, all of the external lattice modes are characterized by a one-phonon-like behavior, while the behavior of the internal modes of the (V,P)O4 tetrahedron is two-phonon-like.

Synthesis, crystal structures and magnetic properties of organically templated new layered vanadates: [C4H8NH2]V3O7, [(CH3)2NH2]V3O7, [C5H10NH2]V3O7 and [C2H5NH3]V3O7

Four new layered mixed-valance vanadium oxides, which contain the interlamellar organic cations pyrolidinium, dimethylammonium, piperidinium, and ethylammonium, have been prepared under hydrothermal conditions and their structures determined. All four structures contain vanadium oxide layers constructed from V5+O4 tetrahedra and pairs of V4+O5 square pyramids with the protonated organic amines occupying the interlayer space. The materials are further characterized by thermal analysis, FTIR and scanning electron microscopy. Magnetic susceptibility studies of the first three compounds reveal a spin-gap behavior explained by an isolated antiferromagnetic dimers model. Large values of the exchange constants J = 325 − 480 K were found and the dependence of J upon the structural parameters was analyzed assuming a kinetic exchange mechanism.

Na4Ni5[(As1−xPx)O4]2[(As2yP2−2y)O7]2(x= 0.27 andy= 0.295)

Crystals of the title compound, tetrasodium pentanickel arsenic–phosphorus (2.64/3.36) docosaoxide, has been grown by a solid-state reaction and characterized by single-crystal X-ray diffraction. The structure is built up from corner- and edge-sharing (AsP)O4 tetrahedra, (AsP)2O7 groups, NiO6 octahedra and Ni2O9 units, giving rise to a polyhedral connectivity having tunnels running along the [001] direction. It is isostructural with Na4Ni5(PO4)2(P2O7)2.

CRYSTAL CHEMISTRY OF URANYL MOLYBDATES. X. THE CRYSTAL STRUCTURE OF Ag10[(UO2)8O8(Mo5O20)

Crystals of a new silver uranyl molybdate, Ag10[(UO2)8O8(Mo5O20)], have been synthesized by high-temperature solid-state reaction. The structure [monoclinic, C2/c, a 24.672(2), b 23.401(2), c 6.7932(4) A, 94.985(2)°, V 3907.3(4) A 3 , Z = 4] was solved by direct methods and refined to R1 = 0.049 (wR2 = 0.101) on the basis of 4317 unique observed reflections using a crystal twinned on (001). The twinning causes overlap of the reflections with l = 3n. The structure is based upon complex double sheets of UrO5 pentagonal bipyramids and Mo polyhedra. The double sheets are parallel to (100) and consist of two [(UO2)2O2(MoO5)] sheets of UrO5 bipyramids and MoO6 octahedra. Within the [(UO2)2O2(MoO5)] sheets, UrO5 bipyramids share edges to produce complex chains parallel to the c axis and linked via pairs of edge-sharing MoO6 octahedra. The two [(UO2)2O2(MoO5)] sheets are linked into double [(UO2)8O8(Mo5O20)] sheets via the Mo(3)O4 tetrahedron located between the sheets. The MoO4 tetrahedra share two corners with two MoO6 octahedra of the sheet above and two corners with MoO6 octahedra from the sheet below, so that Mo5O20 pentanuclear clusters are formed. The uranyl molybdate sheets found in the structure have not been previously observed in uranyl minerals and inorganic compounds. The Ag(2), Ag(3), Ag(6), Ag(7), and Ag(8) atoms are located within the double sheets, whereas the Ag(1), Ag(4), and Ag(5) are in between the double sheets.

The First Sodium Uranyl Chromate, Na4[(UO2)(CrO4)3]: Synthesis and Crystal Structure Determination

AbstractThe first sodium uranyl chromate, Na4[(UO2)(CrO4)3], has been obtained by high‐temperature solid‐state reaction. The structure (triclinic, P1¯, Z = 2, a = 7.1548(3), b = 8.4420(3), c = 11.5102(5)Å, α = 80.203(1)°, β = 79.310(1)°, γ = 70.415(1)° V = 639.24(4)Å3 ) has been solved by direct methods and refined on the basis of F2 for all unique reflections to R1 = 0.024 [calculated on the basis of 4374 unique observed reflections (‖Fo‖ 4σF)]. The structure is based on chains of composition [(UO2)(CrO4)3] that are parallel to [1¯01]. The chains contain UrO5 pentagonal bipyramids (Ur = Uranyl) that share all equatorial corners with CrO4 tetrahedra. Cr(1)O4 and Cr(3)O4 tetrahedra bridge between two adjacent UrO5 bipyramids, whereas Cr(2)O4 tetrahedra share one corner with one UrO5 bipyramid each. The [(UO2)(CrO4)3] chains are planar and oriented parallel to (313). The Na+ cations provide linkage of the chains in the structure.

Oxidative Destruction of Hydrocarbons on a New Zeolite-like Crystal of Ca12Al10Si4O35 Including O2- and O22- Radicals

To develop a nonmetal catalyst to decompose hydrocarbons, a new zeolite-like Ca12Al10Si4O35 was prepared by calcining hydrogarnet, Ca3Al2(SiO4)0.8(OH)8.8, a hydrothermal reaction product from a mixture of CaO, Al2O3 sol, and amorphous SiO2. The X-ray diffraction analysis showed the framework of (Al,Si)O4 tetrahedra formed in the Ca12Al10Si4O35 crystal. ESR measurement and Raman spectroscopy revealed that both superoxide anions (O2-) and peroxide species (O22-) existed in the cavity of the framework. Due to the O2- and O22- species present, Ca12Al10Si4O35 exhibited high activity for the oxidation of hydrocarbons to carbon oxides (CO2 and CO) and H2O at >400 °C.

(NH4)(Zn,Ga)2(PO4)2, an open-framework structure

Ammonium di­(zinc, gallium) bis­(phosphate), (NH4)(Zn,Ga)2(PO4)2, has a zeolite-like open-framework structure. It contains channels of four- and eight-membered rings of alternating tetrahedra of (Zn,Ga)O4 (Zn:Ga ≃ 1:1) and PO4, in which the tetrahedra are connected via corners. The NH4+ cations are located in the channels and provide weak hydrogen bonds to the framework O atoms. The average (Zn,Ga)—O bond lengths of the two non-equivalent (Zn,Ga)O4 tetrahedra are 1.863 and 1.870 Å. All atoms are in general positions. The compound is isostructural with K(CoII,Al)2(PO4)2 and [(NH4)x(NH3)0.5−x]CoxAl1−xPO4 (x = 0.38). Single-crystal Raman and IR spectra are discussed.

Crystal structure of K1- x Cs x BSi2O6 (x = 0.12, 0.50) boroleucite solid solutions and thermal behaviour of KBSi2O6 and K0.5Cs0.5BSi2O6

Abstract The crystal structures of two K1- x Cs x BSi2O6 solid solutions have been refined at room temperature by the Rietveld method: x = 0.12, a = 12.6858(4) Å, Rwp = 7.66%, R F = 5.56% and x = 0.50, a = 12.8480(2) Å, Rwp = 7.64%, R F = 3.10%. They are isostructural to cubic KBSi2O6 with the space group I4̅3d. The structure is built up from (Si,B)O4 tetrahedra linked in four-, six- and eightfold rings which are forming a three-dimensional borosilicate framework. The framework contains large cavities that are placed in continuous channels along the [111] directions. The Cs and K atoms occupy the positions in the channels statistically. Thermal behaviour of KBSi2O6 and K0.5Cs0.5BSi2O6 has been studied by high-temperature powder X-ray diffraction within the temperature range of 293-1073 K. A new tetragonal polymorph of KBSi2O6 has been found in situ under heating. The new polymorphic I4̅3d (cubic) – Ia3̅d (cubic) transition and the new Ia3̅d cubic polymorphic phase has been proposed for K1- x Cs x BSi2O6 from our experimental and literature data on crystal structures and thermal expansion of leucites. The structural relaxation under cationic (K, Cs) substitutions and under heating has been investigated.

Reaction of Hydrogrossular with Hydrogen Chloride Gas at High Temperature

The reaction between hydrogrossular and hydrogen chloride (HCl) gas was performed in a fixed bed reactor above 400 °C. The hydrogrossular was efficiently reacted with HCl gas in the temperature range of 400 to 950 °C and transformed into Ca12Al9.9Si4.05O32Cl5.9 (calcium aluminum chlorosilicate). The crystal structure of the product phase Ca12Al9.9Si4.05O32Cl5.9 was cubic, space group I 3d, with unit cell a = 12.0173(1) A, and was similar to that of wadalite. The structure consists of a framework of (Al,Si)O4 tetrahedra. A large cavity in the framework accommodates Ca−Cl−Ca linearly coordinated atoms.

A powder diffraction study of Sr3Al10SiO20

In tristrontium decaaluminium silicon icosaoxide, Sr3Al10SiO20, (Al,Si)O4 tetrahedra and AlO6 octahedra form a framework. Sr atoms occupy two large cavities of the framework. Sr2 and Al4 are on sites of 2/m symmetry, Al3 is on a twofold axis and Sr1 is on a mirror plane. The remaining Al and Si atoms are disordered over tetrahedral sites on general positions.

Synthesis and Crystal Structure of Novel Layered Manganese Oxide Ca2MnGaO5+δ

New layered oxides Ca2MnGaO5+δ and Ca2MnGa1−xZnxO5+δ (x=0.1, 0.2) were synthesized by solid-state reaction at 1000–1300°C. The crystal structure of Ca2MnGaO5.045 was studied using X-ray, neutron and electron diffraction, and high-resolution electron microscopy (HREM). The samples of Ca2MnGaO5.045 consist of two closely intermixed brownmillerite-type phases with Pnma or Ima2 space symmetry that possess very closely related structures that differ mainly by the orientation of the Ga–O chains. The formal Mn valence (VMn) in Ca2MnGaO5+δ can be varied either by heterovalent replacement of Ga3+ for Zn2+ or by oxygen insertion after treatment under 80 atm O2. In the latter case the compound with the composition Ca2MnGaO5.39 forms built of domains of initial reduced material and fully oxidized Ca2MnGaO5.5 phase. The Ca2MnGaO5.5 structure was determined by HREM as belonging to the brownmillerite AnBn−1B′O3n−1 (n=4) homologous series, in which three layers of BO6 (B=Mn, Ga) octahedra form blocks separated by a single layer of B′O4 (B′=Ga) tetrahedra. The increase of VMn from +3.09 to +3.78 is accompanied by a drastic compression of the structure along the b=4aper axis due to a suppression of the Jahn-Teller deformation of the MnO6 octahedra.

Cation-Exchange Properties of Natural Zeolites

Zeolite minerals are crystalline, hydrated aluminosilicates of alkali and alkaline earth cations characterized by an ability to hydrate/dehydrate reversibly and to exchange some of their constituent cations with aqueous solutions, both without a major change in structure. Because of their ion-exchange, adsorption, and molecular sieve properties, as well as their geographically widespread abundance, zeolite minerals have generated worldwide interest for use in a broad range of applications. Examples of these applications are discussed in other chapters of this book. Of particular interest in this chapter are the cation-exchange properties of zeolite minerals. Due to the favorable ion-exchange selectivity of natural zeolites for certain cations, such as Cs+, Sr2+, and NH4+, these minerals have been studied for potential use in the treatment of nuclear wastewaters (Howden and Pilot 1984; Baxter and Berghauser 1986; Robinson et al. 1995; Pansini 1996), municipal and industrial wastewaters (Kallo 1995; Pansini 1996), and acid mine drainage waters (Bremner and Schultze 1995; Zamzow and Schultze 1995). Natural zeolites have also been studied for potential use in the remediation of sites contaminated with fission products such as 90Sr and 135,137Cs (Leppert 1988; Valcke et al. 1997a; Valcke et al. 1997b) and in the remediation of soils contaminated with heavy metals (Ming and Allen, this volume). Additional interest resulted from the potential siting of a high-level nuclear waste repository at Yucca Mountain, Nevada, which is underlain by diagenetically altered, zeolite-rich (clinoptilolite, heulandite, and mordenite) rhyolitic tuffs (Broxton et al. 1986; Broxton et al. 1987) that could serve as barriers to radionuclide migration to the accessible environment. Zeolites consist of three-dimensional frameworks of (Si,Al)O4 tetrahedra where all oxygen ions of each tetrahedron are shared with adjacent tetrahedra. The presence of Al3+ …

The crystal structure of namibite, Cu(BiO)2VO4(OH), and revision of its symmetry

The crystal structure of namibite, Cu(BiO)2VO4(OH) [triclinic, space group P1̄, a = 6.210(1), b = 7.398(1), c = 7.471(1) Å, α = 90.10(1), β = 108.73(1), γ = 107.47(1)°, V = 308.22(8) Å3, Z = 2] was determined using single-crystal X-ray diffraction data. The refinement, based on 2140 unique reflections with Fo > 4σ(Fo), gave R1 = 3.61%. The structure determination showed namibite to be triclinic-pseudomonoclinic; the previously reported C-centered monoclinic cell is a pseudocell. The structure contains two unique Bi atoms, with nine Bi-O bonds between 2.17 and 3.39 Å. The Bi coordinations show some stereochemical influence of the lone pair of electrons on Bi3+. A threedimensional network is formed by linkages of Bi-O polyhedra to one slightly distorted V5+O4 tetrahedron that decorates chains of corner-sharing CuO6 polyhedra extending parallel to the b axis. The CuO6 polyhedra show the Jahn-Teller-distorted [4+2]-coordination of Cu2+. Layers of Bi atoms parallel to (100) alternate with layers of parallel heteropolyhedral [Cu(VO4)O2(OH)] chains. According to bond-valence calculations and geometrical considerations, the H atom of the OH group is probably involved in disordered or trifurcated H bonding. The structure of namibite represents a slightly distorted ordered variant of the monoclinic structure of brendelite, (Bi,Pb)2(Fe3+,Fe2+)O2(OH)(PO4). Further relations to synthetic Cu3Bi4V2O14, to the 7 Å chain-structure phosphates and sulfates, and to linarite are outlined.

Structured diffuse scattering, displacive flexibility and polymorphism in Ba-hexacelsian

The results of a temperature-dependent electron diffraction study of the low frequency modes of distortion of Ba-hexacelsian and their relationship to the α-β polymorphic phase transition therein are presented. Cs- and Rb-doped Ba-hexacelsian specimens are also investigated. An extremely strong and characteristic diffuse intensity distribution in the form of polarized sheets of diffuse intensity perpendicular to the directions is found for the high temperature polymorph and the doped specimens. The diffuse distribution appears to result from coupled tetrahedral rotation of columns of corner-connected (Al,Si)O4 tetrahedra about the [0 0 1] axis (uncorrelated from column to column as a result of the positioning of the rotation axes).

Effect of Fe2O3 Content on the Local Structure and Crystallization Mechanism of Calcium Gallate Glasses

57Fe Mossbauer and FT-IR of 60CaO·(40-x)Ga2O3·xFe2O3 glasses revealed that Fe(III)O4 tetrahedra occupy substitutional sites of Ga(III)O4 tetrahedra. The activation energy for crystallizaation (E a) obtained from DTA study decreases distinctly from 8.9 to 4.8 eV with an increase in the Fe2O3 content. In the case of 40CaO·(60-x)Ga2O3·xFe2O3 glasses, a week doublet due to Fe(II)O4 tetrahedra or Fe(III)O6 octahedra was observed in addition to Fe(III)O4 tetrahedra. The E avalue decreases gradually from 7.1 to 5.6 eV with an increasing Fe2O3 content. These results indicate that a large amount of Fe2O3 in the network structure is favorable for the crystallization of calcium gallate glass, since it reduces the chemical bond strength.