Types Of Framework Structures Research Articles

Two Structure Types Based on Si6O15 Rings: Synthesis and Structural and Spectroscopic Characterisation of Cs1.86K1.14DySi6O15 and Cs1.6K1.4SmSi6O15

AbstractThe silicate Cs1.86K1.14DySi6O15 represents a mixed tetrahedral‐octahedral framework structure type based on roughly circular Si6O15 rings and isolated DyO6 octahedra. The silicate Cs1.6K1.4SmSi6O15 has a layered atomic arrangement built from corrugated Si6O15 layers containing four‐, six‐ and eight‐membered rings. The layers are connected by isolated SmO6 octahedra to form a mixed tetrahedral‐octahedral framework. This structure shows a close structural relationship to β‐K3NdSi6O15 and a less close one to dehydrated elpidite (Na2ZrSi6O15). In both structures, Cs/K atoms occupy large voids. The silicates were obtained through high‐temperature flux syntheses. Their crystal structures have been determined from single‐crystal X‐ray diffraction data. Cs1.86K1.14DySi6O15 crystallises in R32 (no. 155) with a = 13.896(2), c = 35.623(7) Å and V = 5957.2(17) Å3, whereas Cs1.6K1.4SmSi6O15 crystallises in Cmca (no. 64) with a = 14.474(3), b = 14.718(3), c = 15.231(3) Å and V = 3244.7(11) Å3. The Dy3+ and Sm3+ cations present in the silicates cause PL emission bands in the visible yellow‐to‐orange spectral range.

High-pressure polymorph of phosphorus nitride imide HP₄N₇ representing a new framework topology.

A new polymorph of phosphorus nitride imide HP4N7 has been synthesized under high-pressure/high-temperature conditions from P3N5 and NH4Cl at 6 GPa and temperatures between 800 and 1300 °C. Its crystal structure was elucidated using single-crystal X-ray diffraction data. β-HP4N7 (space group C2/c, no. 15, Z = 4, a = 12.873(2) Å, b = 4.6587(4) Å, c = 8.3222(8) Å, β = 102.351(3)°, R1 = 0.0485, wR2 = 0.1083) crystallizes in a new framework structure type that is made up of all-side vertex-sharing PN4 tetrahedra. The topology of the network is represented by the point symbol (3(2).4(2).5(2).6(3).7)(3(4).4(4).5(4).6(3)), and it has not been identified in other compounds so far. Structural differences between the two polymorphs of HP4N7 as well as the topological relationship to the recently discovered high-pressure polymorph β-HPN2 are discussed. Additionally, FTIR and solid-state NMR spectroscopy are used to corroborate the results of the structure determination.

Layered precursors for new zeolitic materials: Synthesis and characterization of B-RUB-39 and its condensation product B-RUB-41

Condensation of layered silicate precursors leads to new, all silica zeolite frameworks. In order to introduce catalytic functionality, boron has been substituted into the silicate layer of RUB-39 in a single step synthesis process. Condensation of the silicate layer to the zeolite framework of RUB-41, RRO framework structure type, preserved B as constituent of the material. Analysis of structural details obtained from Rietveld analysis of powder diffraction data, 11B and 29Si NMR experiments of the as synthesized precursor as well as of the zeolite condensation product, and crystal chemical reasoning indicates segregation of B on one specific T-site. This T-site is buried in the silicate anionic layer of the precursor shielding the additional negative charge introduced by the trivalent T-atom.

Synthesis and Characterization of Low Loading MoO3/Ts-1 Catalyst

⎯Molybdenum oxide (MoO3) have been introduced to titanium silicalite (TS-1) by impregnation methode and have been characterized with X-ray diffraction (XRD), infrared spectroscopy, nitrogen and pyridine adsorption. The results show that TS-1 and XMoO3/TS-1 have orthorhombic structure and MFI framework structure type. 0,5% MoO3/TS-1, dan 1% MoO3/TS-1 catalyst have not been yet Brønsted acid site, while Brønsted acidity increased from 2% MoO3/TS-1 to 4% MoO3/TS-1 respectively.

オーバーデンチャー支台歯上の補強法に関する研究

This study investigated the effect of the position of reinforcement wires, differences in artificial teeth, and framework designs on the breaking strength of overdentures. The basal surfaces of composite resin teeth and acrylic resin teeth were removed using a carbide bur. A reinforcement wire or a wrought palatal bar was embedded near the occlusal surface or basal surface. Four types of framework structures were designed : conventional skeleton (skeleton), housing with skeleton (housing), housing plus short metal backing (metal backing), and housing plus long metal backing (double structure). After the wires, bars, and frameworks were sand-blasted with 50 microm Al(2)O(3) powder, they were primed with a metal primer and embedded in a heat-polymerized denture base resin. The breaking strengths (N) and maximum stiffness (N/mm) of two-week aged (37 degrees C) specimens were measured using a bending test (n=8). All data obtained at a crosshead speed of 2.0 mm/min were analyzed by ANOVA/Tukey's test (alpha=0.01). There were no statistical differences between the two kinds of artificial teeth (p>0.01). The wrought palatal bar had significantly higher strength than the reinforcement wire (p<0.01). Greater strengths were found for specimens with frameworks than those without frameworks (p<0.01). The breaking strength of the wrought palatal bar embedded near the occlusal surface was higher than that on the basal surface (p>0.01). The breaking strength and maximum stiffness of the double structure framework were significantly greater (p<0.01) than those of the conventional frameworks. The breaking strengths of overdentures were influenced by the size and position of the reinforcement wires. Double structure frameworks are recommended for overdentures to promote a long-term prognosis without denture breakage.

Synthesis and crystal structure of a new microporous silicate with a mixed octahedral-tetrahedral framework: Cs3ScSi8O19

AbstractDuring investigations of the system Sc2O3-Al2O3-TiO2-SiO2, a new, unusual microporous compound, Cs3ScSi8O19, was synthesized as colourless plates from a CsF-MoO3 flux. The crystal structure was determined from single-crystal X-ray diffraction data (Mo-Kα radiation, CCD area detector). The compound is orthorhombic, space group Pnma, with a = 11.286(2), b = 7.033(1), c = 26.714(5) Å, and Z = 4 (R1(F) = 2.6% and wR2all(F2) = 7.3%, using 3066 ‘observed’ reflections with Fo &gt; 4σ(Fo)). The crystal structure of Cs3ScSi8O19 represents a new microporous framework structure type (‘MCV-1’), and the compound is exceptional in being the first representative of a mixed octahedral-tetrahedral framework structure, in which the [TO4]:[MO6] ratio is &gt;6:1. The structure is based on isolated, nearly regular ScO6 octahedra [dav(Sc—O) = 2.112 Å] sharing corners with SiO4 tetrahedra to form an open framework with four-, six- and eight-membered rings; the latter are formed by SiO4 tetrahedra only. Two fully occupied Cs positions are located in large framework voids close to the six-membered rings, whereas four partly occupied and disordered Cs positions are close to very large framework voids bordered by the puckered eight-membered rings. The cavities are linked into channels parallel to [100] and [010]. The structure is compared with that of Cs2TiSi6O15 and related microporous scandium-, REE-, titano- and zirconosilicate minerals and compounds. Cs3ScSi8O19 or derivatives may be important in the context of immobilization of radioactive 137Cs waste, cationic conductivity or catalysis.

Correlation of 129Xe NMR shielding data with the pore structures of various aluminophosphate molecular sieves

129Xe NMR spectra of two different amounts of xenon sealed inside sample tubes containing various microporous aluminophosphate (AlPO-5, -11, -31, and -41) and silicoaluminophosphate (SAPO-5, -11, -31, and -41) molecular sieves are recorded at different temperatures and analysed. For most cases, the 129Xe shielding tensor of adsorbed xenon is asymmetric and distinct spectral differences between circular and elliptical cross-sections, framework dimensions, and xenon loading levels of sieve channels are detected based on the powder pattern lineshape fittings. The roles of Xe–wall and Xe–Xe interactions and different adsorbant diffusion modes on spectral characteristics are discussed. The shielding tensor axes are associated with the sieve channel planes by comparing the data with previously published limiting case models of lineshapes. Shielding tensor span is found to be a promising indicator of sieve channel dimensions. Small differences between AlPO and SAPO molecular sieves belonging to the same framework structure type are also detected. In AlPO-31, fast exchange effects between Xe in the free intercrystallite volume and Xe physisorbed on the external crystallite surfaces are observed and the intercrystallite cavity sizes are estimated.

(3 + 1)-Dimensional structure refinement of the fresnoite framework-structure type compound Ba2TiGe2O8

The incommensurately modulated structure of the fresnoite framework-structure type compound Ba(2)TiGe(2)O(8) has been solved using a (3 + 1)-dimensional superspace approach. The structure is orthorhombic and adopts the superspace group Cmm2(0,beta,1/2)s00 with beta approximately 0.635 at room temperature. The refinement was based on neutron powder diffraction data obtained from a powdered single crystal grown by Czochralski pulling. The modulation parameters that were obtained support the idea that frozen-in rigid-unit modes cause the modulation. The modulation is mainly manifested by positional displacements of O atoms. Barium ions are either eightfold, ninefold or tenfold coordinated in the one-dimensional modulated structure. A significant improvement of the bond-valence sum for both barium positions is achieved by the introduction of the positional modulation. This finding strongly suggests that underbonded barium positions are critically involved in provoking the incommensurate modulation in Ba(2)TiGe(2)O(8).

Bending Strengths of Metal Framework Structures for Implant-stabilized Overdentures

Purpose : This study evaluated the bending strengths of five types of framework structures for implant-stabilized overdentures.Materials and Methods : Five types of framework structures for implant-stabilized removable prostheses were cast using a Co-Cr alloy : conventional housing (Type A), housing with short skeleton (Type B), long skeleton only (Type C), housing with long skeleton (Type D), and Type D plus a metal backing connected by columns (Type E ; hereinafter referred to as the “double structure”). All castings were embedded in a heat-cured denture base resin. As controls, the same size resin blocks without frameworks were prepared. A bending test was used to test each specimen as it acted as a fulcrum on the implant. Breaking load, maximum stiffness, and strain were measured.Results : The breaking load and maximum stiffness of the double structure were significantly greater (p<0.05), i.e., 1.5-4.5 times and 2-6 times greater, respectively, than for the conventional frameworks.Conclusion : When the double structure framework was used for implant-stabilized prostheses, the bending strengths were greater than for the conventional housing design.

Synthesis and Crystal Structure of Open Framework Zinc‐Cobalt Phosphate with Zeolite DFT Topology.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A TEM and RUM study of the inherent displacive flexibility of the fresnoite framework structure type

A careful electron diffraction study has been made of the incommensurately modulated room-tem- perature phases of the fresnoites Ba2TiGe2O8 (BTG) and Ba2TiSi2O8 (BTS) and used to determine their (3+1)- and (3+2)-dimensional superspace group symmetries. The primitive primary modulation wave vectors in both materials are found to occur close to the same position in the parent Brillouin zone, near � 0:3h110i � þ 1=2c �. A rigid unit mode (RUM) analysis of the inherent dis- placive structural flexibility of the ideal fresnoite framework structure type is then carried out in an at- tempt to understand the significance of this particular modulation wave vector. Six zero-frequency RUM modes and two close to zero frequency quasi-RUM (Q-RUM) modes are found to exist for any modulation wave vector. These RUM modes are all primarily associated with rotations of the constituent TO4 (T ¼ Si or Ge) tetrahedra and TiO5 square pyramids around in-plane i.e. perpendicular to c rotation axes. A seventh RUM mode involving rotation of the constituent rigid polyhedra around c combined with shifts in the basal plane is found but only at a very specific modulation wave vector q � 0:30h110i �, in close agreement with the condensed RUM mode found in the electron diffraction study. It is the condensation of just such a RUM mode that appears to play a major role in the various incommensurately modulated structures ob- served in Ba2TiGe2O8 ,B a 2TiSi2O8 and Sr2TiSi2O8, re- spectively.

Synthesis and Crystal Structure of Open Framework Zinc-Cobalt Phosphate with Zeolite DFT Topology

The synthesis and crystal structure of Zn (2-x) Co x (PO 4 ) 2 (NH 3 H 2 CH 2 NH 3 ) (x = 0.61) (ZCP-DFT) is described. ZCP-DFT is characterized by means of single-crystal and powder X-ray diffraction. Crystal data for ZCP-DFT: tetragonal, space group P4 2 bc (No. 106), a = 14.7236(6) A, b = 14.7236(6) A, c = 8.9544(5) A, V = 1941.17(16) A 3 , Z = 8. The structure has 3-D 8-ring channel system with protonated ethylenediamine cations in the channel junctions. The framework structure type is the same as the zeolite DFT topology. The synthesis of ZCP-DFT indicates that cobalt can partially substitute the metal sties of zinc phosphate, which can lead to the modification of physical and chemical properties of the parent compounds.

Characterization of a New Microporous Lithozincosilicate with ANA Topology

A new microporous lithozincosilicate (Cs 12 Li 13 [Li 3 Zn 8 Si 37 O 96 ].4H 2 O), an analogue of pollucite (CsAlSi 2 O 6 ) and analcime (NaAlSi 2 O 6 ), contains lithium in both framework and nonframework sites. This represents the first example of the incorporation of lithium into the ANA framework structure type. The analysis of the crystal structure used X-ray and neutron powder diffraction techniques, which reveal partially ordered sites in the framework occupied by Li, Zn, and Si atoms. The framework sites are occupied in a manner to distribute the low valent cations as far apart as possible. The pore system of the material consists of large cuboctahedra, occupied by Cs and water molecules, and smaller vacancies available for siting of nonframework Li bounded by six- and eight-membered rings of framework tetrahedra.

Joint Strengths of Metal Framework Structures for Removable Partial Dentures

Purpose : This study investigated the joint strengths of two frameworks for removable partial dentures (RPD) embedded in a denture base resin.Materials and Methods : Six types of framework structures were cast conventionally from a Co-Cr alloy. To connect two castings, six types of joints were designed : Type A (butt joint), Type B (soldered butt joint), Type C (soldered lap joint), Type D (10 mm overlapped T-shape), Type E (20 mm overlapped T-shape), and Type F (Type D with two pins). Two castings were embedded in denture base resin and finished to a size of 10.0×10.0×65.0 mm. As a control, the same size resin block without a framework was prepared. Joint strengths were determined using a three-point bending test. To evaluate the strength change after rejoining, the broken specimens were reconnected using the same resin and tested as in the first test.Results : Both the breaking load and maximum stiffness of Types D, E, and F were significantly (p 0.05) different between the before- and after-repair state.Conclusion : Because of the design of the three-dimensional RPD frameworks, greater joint strengths were obtained than for the conventional soldered framework design.

Raman Spectroscopic Identification of Fibrous Natural Zeolites

Laser Raman microprobe spectra of the natrolite group of zeolites (fibrous hydrous network aluminosilicates) can be used to unambiguously distinguish among the six members of this group, which is difficult by visual, microscopic, and X-ray diffraction methods. The natrolite group of zeolites includes the following minerals: natrolite (Na2Al2Si3O10·2H2O), scolecite (CaAl2Si3O10·3H2O), mesolite (Na2Ca2Al6Si9O30·8H2O), thomsonite (NaCa2Al5Si5O20·6H2O), gonnardite (Na2CaAl4Si6O20·7H2O), and edingtonite (BaAl2Si3O10·4H2O). Accurate locations of peak maxima are given, and complete Raman spectra (from 100 to 4000 Δcm−1) are shown for each mineral. The individual members of this structurally very similar group of minerals can be identified on the basis of the exact Raman peak positions of the two strongest bands near 440 and 535 Δcm−1, the number and positions of weaker bands, and the difference in the dependence of peak intensities upon beam polarization direction. However, the minerals can be especially easily identified on the basis of their strikingly different Raman spectral patterns in the O–H stretching region (3000–3700 Δcm−1). The number and width of peaks in this spectral region correlate with the three different types of framework structures that occur among the natrolite group minerals.

Crystal Structures and Electronic Absorption Spectra of Two Modifications of Cr(SeO2OH)(Se2O5)

Single crystals of two modifications (I and II) of Cr(SeO2OH)(Se2O5) have been synthesized under low-hydrothermal conditions. Their structures have been investigated using single-crystal X-ray diffraction data up to sinθ/λ=0.76 Å−1[I: monoclinic, space groupP21/n,a=7.517(2) Å,b=12.516(3) Å,c=7.381(2) Å,β=91.46(1)°,Z=4,R1=0.030 for 1562Fo>4σ(Fo) and 114 variables; II: orthorhombic, space groupPnma,a=8.782(2) Å,b=11.172(3) Å,c=7.545(2) Å,Z=4,R1=0.031 for 752Fo>4σ(Fo) and 65 variables]. In Cr(SeO2OH)(Se2O5)-I, sheets—built up from isolated CrO6octahedra and Se2O5groups—are linked via the SeO2OH groups and rather strong hydrogen bonds. This structure is isotypic with the corresponding compounds of Mn(III) and Fe(III). Cr(SeO2OH)(Se2O5)-II represents a new framework structure type, also composed of isolated CrO6octahedra and Se2O5and SeO2OH groups, but with very weak hydrogen bonds. The hydrogen-bonding schemes of both compounds were further investigated by FTIR microscope spectrometry in the range 7000–1000 cm−1, yielding a typical AB-band spectrum for phase I. Furthermore, polarized electronic absorption spectra were measured in the range 33,000–12,500 cm−1using UV–VIS microscope spectrometric techniques. According to the weak distortions of the CrO6octahedra in both compounds, the observed band splittings and polarization effects are rather weak. Hence, crystal field calculations were performed assumingOhsymmetry, resulting in the following crystal field parameter sets; I,Dq=1558,B35=653,B55=760,C=2920 cm−1; II,Dq=1641,B35=647,B55=730,C=2815 cm−1. TheseDqvalues are slightly below average compared to octahedral Cr(III) in other oxygen-based structures, a tendency that was already observed for other 3dtransition elements in crystal fields of selenite compounds. This might indicate a rather low position of the [SeO3]2−anion within the range of oxygen-based ligands in the spectrochemical series.

Syntheses and Characterizations of Chiral Tetrahedral Cobalt Phosphates with Zeolite ABW and Related Frameworks

The hydrothermal syntheses, X-ray crystal structures, and magnetic properties of a family of 3-D chiral framework cobalt phosphates are presented. Two different types of framework structures are described: one has the same topology as the well-known zeolite ABW framework and represents the only pure cobalt phosphate framework with a known zeolite topology; the other exhibits a framework connectivity which can be considered as a hybrid of tridymite and ABW frameworks. These new chiral materials were obtained by systematic chemical variation, accurate control of solution pH values, and use of non-aqueous solvents. Synthesis conditions were found which favored the crystallization of Co2+ oxygen tetrahedra in strict alternation with P5+ oxygen tetrahedra from cobalt phosphate solutions in the presence of Na+, K+, NH4+, or Rb+ ions. The transition from one framework type to the other is affected by the size of these extra-framework cations. The two ABW structures (NH4CoPO4-ABW, RbCoPO4) have eight-ring channe...