Pyramidal Units Research Articles

Synthesis and structures of the first triiodoarsenate(III) anion, EtAsI3−, and zwitterions, (HPy)2As2I6

The first examples of organotriiodoarsenates(III) in the form of zwitterions, (3-HPy)2As2I6 and (4-HPy)2As2I6, have been obtained from aqueous solutions, and their structures have been established by XRD. The dimeric molecules in the crystals are built from two square pyramidal (HPy)AsI4 units joined by 2 bridging I atoms. The crystal packing of both compounds is largely defined by interlayer As⋯I contacts, which fulfill the coordination sphere of the As atoms to 6 in the 4-HPy isomer and result in its characteristic red colour and lower solubility. These intermolecular interactions in the crystal structure can be suppressed by the inclusion of a solvent, showing them to be not very strong. The intramolecular bonding via the two bridging I atoms was proven to be rather weak as well, by the formation of the salt [Et4N][EtAsI3] with a monomeric triiodoarsenate(III) anion from acetonitrile solution. In the closely related compound p-H2NC6H4AsI2·HI, one iodide can be substituted for the OTs− anion to give [p-H3NC6H4AsI2]OTs, showing the iodide belongs to the outer sphere rather than being coordinatively bound to the As atom. The lengths of the trans-I–As–I bonds in the determined structures can be formalized by a semi-empirical modified Pauling equation, which relates them to the bond order, taking into account the antibonding influence of the 4s orbital of the As atom.

Experimental and Numerical Study for the Shaping Formation of SCST Structures by Cable-tensioning

This paper discusses the behaviour characteristics of the shaping formation of Single-Chorded Space Truss (SCST) structures by means of cable-tensioning of bottom chords. The innovative technique is fast and economical and issued in many types of space structures. The small-scale test models presented herein consist of uniform pyramids with multi-directional ball type joints which are erected into their final shape by cable-tensioning. Since the joint behaviour is very significant in studying the shaping of SCST structures, basic tests for beam and pyramidal units were performed. The feasibility of the proposed cable-tensioning technique and the reliability of the established geometric model were confirmed by finite element analysis. The proposed cable-tensioning technique indicates that the behaviour characteristic of joints is very important in the shaping formation of SCST structures. More specifically in situations where heavy cranes are inaccessible, the cable-tensioning construction technique has proven to be an easy and reasonable method compared to conventional construction methods that typically include heavy cranes and scaffolding.

ChemInform Abstract: Chromium(V) Oxide Trichloride, and Some Pentachlorido‐oxido‐chromate(V) Salts: Structures and Spectroscopic Characterization.

AbstractCrOCl3 crystallizes in the monoclinic space group P21/c with Z = 4 (single crystal XRD).

Optical absorption and structural studies of bismuth borate glasses containing Er3 + ions

Glasses with composition xBi2O3–24Na2O–(75−x)B2O3–1Er2O3 (where x=0, 5, 10, 15, 25, 33, 40mol%), were prepared by the melt quenching technique. The effect of Bi2O3 content on thermal stability, optical properties and structures of these glasses is systematically investigated by X-ray diffraction, infrared spectroscopy and DTA techniques. The variations in the optical band gap energies, with Bi2O3 content have been discussed in terms of changes in the glass structure. Urbach energy increases with increasing Bi2O3 content in the present glass system. It is found that the density, molar volume and optical basicity increase with increasing Bi2O3. The glass transition temperature (Tg) of the samples was found to decrease with the Bi2O3 content. IR measurements revealed an existence of trigonal BO3 pyramid, tetrahedron BO4, pyramidal BiO3 and octahedron BiO6 structural units in the network of the investigated glass. Furthermore, a decrease in BO4 and an increase in BO3 take place against the increase of x which means that, Bi2O3 plays the role of network modifier in the structural network.

IR, UV–vis spectroscopic and DSC investigations of europium doped tellurite glasses obtained by sol–gel synthesis

FTIR, UV–vis spectroscopy and DSC studies were utilized in order to study structural changes produced by the variation of the Eu(NO3)3 content in binary europium–tellurite glasses obtained using the sol–gel method. Our results show that the europium ions can be considered as modifiers because they will produce the transformation of [TeO4] and [TeO6] structural units into [TeO3] trigonal pyramidal units and the formation of a significant number of non-bridging oxygen ions.UV–vis studies show that the higher Eu(NO3)3 concentrations (24mol%) in the host matrix induce a growth of the number of 4f–4f electronic transitions of the Eu+3 ions and a increase of the number of non-bridging oxygen ions in the regions between 325 and 600nm.In brief, partial replacement of TeO bonds by EuO ionic bonds induces a global weakening of the network explaining the decrease of the glass transition temperature and crystallization temperature by gradually increasing of europium ions in the matrix network.

Chromium(V) Oxide Trichloride, and some Pentachlorido‐­oxido‐chromate(V) Salts: Structures and Spectroscopic ­Characterization

AbstractCrystalline CrOCl3 contains [Cl2OCr(μ‐Cl)2CrOCl2] molecules with two square pyramidal CrOCl4 units sharing a common edge and with the Cr–O arranged anti, a new structure type for transition metal MOX3 compounds. Crystals are monoclinic with space group P21/c, Z = 4, with a = 5.735(5), b = 13.738(7), c = 11.318(4) Å, α = 90°, β = 98.346(6)°, γ = 90°. Its IR and UV/Vis spectra are reported and compared with those of the C3v monomer found in the gas phase. Structures are also reported for M2[CrOCl5] (M = Cs or Rb) and show a pseudo‐octahedral anion. Cs2[CrOCl5] adopts a K2PtCl6‐type structure with [CrOCl5]2– ions randomly orientated, but Rb2[CrOCl5] is orthorhombic with space group Pnma with a = 13.6471(7), b = 9.9175(5), and c = 6.9562(4) Å. Rietveld refinement of the data on the rubidium salt gave Cr–O = 1.628(1), Cr–CltransO = 2.652(7), Cr–CltransCl = 2.239(8)–2.342(3) Å. Corresponding CrV oxide bromide species do not form.

Wavelength Dependence of Photostructural Transformations in As2S3 Thin Films

Abstract Spectral dependence of photostructural transformations on the surface and in the interior of thermally evaporated As 2 S 3 thin films is studied under the influence of bandgap, sub-bandgap and super-bandgap light. For the given light intensity (W~15 mW/cm 2 ) the irradiation by bandgap and super-bandgap light leads to partial restoration of pyramidal structural units in the film, which is a characteristic of the bulk glasses of this stoichiometric composition. The mechanism of photostructural transformations on the surface of the film exhibits strong spectral dependence. S- rich layer is formed upon irradiation by super-bandgap UV light. The sub-bandgap light does not cause any noticeable photostructural transformations at this light intensity.

Influences of Artificial Reefs on Juvenile Red Snapper along the Mississippi Gulf Coast

AbstractRed Snapper Lutjanus campechanus represent one of the more economically important fisheries in the northern Gulf of Mexico; as such, Red Snapper abundance has decreased dramatically in the past two decades. The use of artificial reefs could aid in the rehabilitation of Red Snapper stocks by providing refuge for juveniles and a place of foraging and recruitment. A study was initiated to determine the effectiveness of different artificial reef distribution patterns in attracting and sustaining juvenile Red Snapper in the northern Gulf of Mexico. Fish traps (0.97 m long; 0.64 m high; funnel mouth size = 175×115 mm) were used to collect Red Snapper (<406 mm TL) that were associated with pyramid‐shaped artificial reef structures (3.7‐m triangular base; 2.4‐m height; 3.2 metric tons) to evaluate two reef distribution designs: (1) five closely spaced pyramid units (“clumped” pattern) and (2) five closely spaced pyramids plus two sets of two pyramids at 30.5, 61.0, or 91.5 m from the five pyramids (“outlier” pattern). In 26 sampling trips, 927 Red Snapper were captured. Catch per unit effort (number of fish/trap soak‐hour) did not differ significantly among artificial reef patterns (P = 0.396). Red Snapper TLs differed significantly among patterns (P = 0.005), with the largest mean TL (235 mm; SE = 5.14) occurring at the outlier pattern with 61.0‐m spacing. Results from this study indicate that reef spacing and horizontal extension are important factors to consider when designing an artificial reef program, especially those that target juvenile Red Snapper.Received February 2, 2012; accepted September 26, 2012

Mechanisms of network collapse in GeO2 glass: high-pressure neutron diffraction with isotope substitution as arbitrator of competing models

The structure of the network forming glass GeO2 is investigated by making the first application of the method of in situ neutron diffraction with isotope substitution at pressures increasing from ambient to 8 GPa. Of the various models, the experimental results are in quantitative agreement only with molecular dynamics simulations made using interaction potentials that include dipole-polarization effects. When the reduced density ρ/ρ0 ≳ 1.16, where ρ0 is the value at ambient pressure, network collapse proceeds via an interplay between the predominance of distorted square pyramidal GeO5 units versus octahedral GeO6 units as they replace tetrahedral GeO4 units. This replacement necessitates the formation of threefold coordinated oxygen atoms and leads to an increase with density in the number of small rings, where a preference is shown for sixfold rings when ρ/ρ0 = 1 and fourfold rings when ρ/ρ0 = 1.64.

Raman Scattering Study on Vibrational Modes and Structure of Lanthanum Tellurite Glasses

Raman spectra of xLa2O3-(1−x)TeO2 (x=0, 0.05, 0.10, 0.15, 0.20, and 0.25) lanthanum tellurite glasses were measured and analyzed over the entire glass-forming region in an effort to quantitatively follow the structural changes caused by lanthanum oxide variation. For the first time, systematic intensity measurements have been performed to elucidate the composition induced structural changes in the high-frequency stretching vibration region and a possible mechanism was proposed. The network structure of the glasses is formed by mixing TeO4 trigonal bipyramid and TeO3 trigonal pyramid units. The change of the lanthanum oxide content results in conversion of the TeO4 units to TeO3 units with a varying number of non-bridging oxygen atoms. Analysis of the Raman band contours in terms of vibrations due to different oxygen bridged trigonal bipyramid and trigonal pyramid tellurite structural units, allowed to calculate the relative amounts of the species involved in the structural changes with composition. The fraction of the terminal oxygen atoms has been estimated from the Raman intensities with the aid of a structural model concerning the structure of tellurite network systems. The simulation of the experimental density of lanthanum tellurite glasses with modifier content up to 25% revealed that the short range order building units assumed here are sufficient to account for the overall structure in these glasses.

Manifestation of thermodynamic glass transition by structure and picosecond dynamics in alkali tellurite glasses

The Raman spectra of the 0.1Cs2O–0.9TeO2 melt were measured and analyzed over a broad temperature range including the glassy, supercooled and molten state in an effort to follow the varying structural and dynamical aspects caused by temperature and alkali modifier. The network structure of the glass/melt is formed by mixing TeO4 trigonal bipyramid and TeO3 trigonal pyramid units. Changing alkali content and/or temperature results to conversion of the TeO4 units to TeO3 units with a varying number of non-bridging oxygen atoms. The low-frequency Raman spectra reveal a well-resolved Boson peak whose frequency also depends on temperature. The variation of the maximum of the Boson peak has been determined and discussed in the framework of current phenomenological models. The short-time dynamics of the system experiences drastic changes when approaching the glass-to-liquid transition. The temperature dependent plot of the correlation times extrapolates to a crossover value, which we assign as spectral evidence of the system's known thermodynamic glass transition temperature. Similar behavior exhibit several spectral features, such as the maximum of the Boson peak, the exponent of the susceptibility and the intensity ratio related to the structural transformation from TeO4 tbp to TeO3 tp species occurring in the medium range order structure.

Dioxygen Oxidation Cu(II) → Cu(III) in the Copper Complex of cyclo(Lys-dHis-βAla-His): A Case Study by EXAFS and XANES Approach

A former spectroscopic study of Cu(II) coordination by the 13-membered ring cyclic tetrapeptide c(Lys-dHis-βAla-His) (DK13), revealed the presence, at alkaline pH, of a stable peptide/Cu(III) complex formed in solution by atmospheric dioxygen oxidation. To understand the nature of this coordination compound and to investigate the role of the His residues in the Cu(III) species formation, Cu K-edge XANES, and EXAFS spectra have been collected for DK13 and two other 13-membered cyclo-peptides: the diastereoisomer c(Lys-His-βAla-His) (LK13), and c(Gly-βAla-Gly-Lys) (GK13), devoid of His residues. Comparison of pre-edge peak features with those of Cu model compounds, allowed us to get information on copper oxidation state in two of the three peptides, DK13 and GK13: DK13 contains only Cu(III) ions in the experimental conditions, while GK13 binds only with Cu(II). For LK13/Cu complex, EXAFS spectrum suggested and UV-vis analysis confirmed the presence of a mixture of Cu(II) and Cu(III) coordinated species. Theoretical XANES spectra have been calculated by means of the MXAN code. The good agreement between theoretical and experimental XANES data collected for DK13, suggests that the refined structure, at least in the first coordination shell around Cu, is a good approximation of the DK13/Cu(III) coordination species present at strongly alkaline pH. All the data are consistent with a slightly distorted pyramidal CuN(4) unit, coming from the peptide bonds. Surprisingly, the His side-chains seemed not involved in the final, stable, Cu(III) scaffold.

Infrared and Raman spectroscopic studies of alkali bismuth borate glasses: Evidence of mixed alkali effect

Mixed alkali bismuth borate glasses of composition xLi2O–(30−x) K2O–10 Bi2O3–55 B2O3:5 V2O5 (LK-series) were prepared by melt quench technique. The amorphous nature of these samples was confirmed from their X-ray diffraction. The density of the samples was measured using Archimedes principle and the molar volumes were determined from the density data. The glass transition temperature of the samples was found to vary non-linearly with the Li2O content (x). The spectroscopic properties of glass samples were studied using infrared (IR) and Raman spectroscopic techniques. IR measurements indicate that the network structure of the studied glasses is based on the BiO3 pyramidal and BiO6 octahedral units and also on BO3 and BO4 units. Raman spectra of these alkali combinations with V2O5 present drastic changes in the intensity of various Raman bands. The observation of disappearance and reappearance of some IR and Raman bands and non-linear variation of the peak positions of some of these bands with x is an important result pertaining to the mixed alkali effect in this glass system. Acting as complimentary spectroscopic techniques, both types of measurements IR and Raman revealed that the network structure of the studied glasses is mainly based on BO3 and BO4 units placed in different structural groups, BO3 units being dominant and bismuth exists as BiO3 and BiO6 octahedral units.

The Reactions of Thianthrene and Selenanthrene with AlCl3: Coordination Complexes, Radical Ions, and Investigations on the Unique Triple‐Decker Molecule (Thianthrene)32+

AbstractThe reactions of thianthrene (TA) and selenanthrene (SeA) with AlCl3 were studied in the melt phase and with liquid SO2 as solvent. From neat AlCl3 and TA, the colorless complex [AlCl3(TA)] was isolated as the main product and the dark red salt (TA)3[Al2Cl7]2 as the byproduct. The analogous solvent‐free reaction of selenanthrene and AlCl3 takes a different course as colorless [Al(SeA)3][Al2Cl7]3 is formed in quantitative yield. With SO2 as solvent, both TA and SeA give the black radical salts (TA)2[AlCl4]2 and (SeA)2[AlCl4]2, respectively. In the structure of [AlCl3(TA)], thianthrene acts as a monodentate ligand and coordinates with one S atom to the pyramidal AlCl3 unit. The structure of the (TA)32+ ion is a stack of three almost planar TA molecules in parallel arrangement. [Al(SeA)3]3+ represents a tris‐chelate complex ion with SeA acting as a bidentate ligand and both Se atoms binding to the octahedrally coordinated Al3+ ion. (SeA)2[AlCl4]2 consists of dimers of SeA+ radical ions, which are bound by weak intermolecular Se···Se bonds. Tentative reaction equations are given to explain the unexpected oxidation processes that lead to the radical ions. Quantum chemical calculations were performed on the molecular fragments and on the periodical structures. The trimeric (TA)32+ ion is in the singlet state in accordance with the magnetic properties of (TA)3[Al2Cl7]2, which show a weak temperature‐independent paramagnetism. The ion is bound by long‐range four‐center bonds between the outer two radicals.

Exploratory syntheses, structures, and photoluminescent properties of three lead multi-dimensional frameworks

Three structurally diverse PbII coordination complexes, [Pb3O(OH)(4-sphth)]2(H2O) (1), [Pb(3,5-Hdhb)]H2O (2), and [Pb3(4-nphth)2(OH)2] (3) (4-H3sphth, 4-sulfophthalic acid; 3,5-H2dhb, 3,5-dihydroxybenzoic acid; 4-H2nphth, 4-nitrophthalic acid), were synthesized under hydrothermal conditions. X-ray diffraction analyses reveal that 1 is constructed from [Pb4O4] cubanes, based on which ladder-shaped structure is built via 4-H3sphth bridge. This is the first Pb4O4-containing polymer. The Pb2O2 units in 2 are bridged by two parallel 3,5-HDHB ligands along the a-axis and two other parallel 3,5-HDHB ligands along the b-axis, forming a 3-D framework. For 3, the crystal structure is built up of a layer motif consisting of corner-sharing pyramidal Pb3O units, which are linked through Pb corners to form a hexagonal unit. Each PbO6 polyhedron is connected to three polyhedra (Pb3O) via sharing an edge (two μ 3-oxygen atoms) and two faces (three μ 3-oxygen atoms), thus yielding an infinite 2-D Pb–O–Pb (3,6-net) honeycomb layer. The luminescence of 1–3 demonstrates that they may be good candidates for luminescent materials.

Influence of Mesh Density and Element Type on the Accuracy of FE Analysis of Periodic Cellular Structures

Metallic sandwich panels based on lattice cell structures have been developed for a wide range of potential applications with their lightweight and multi-functionality. Structural performance of sandwich panels can be predicted from the studies on the mechanical properties of a unit cell. Numerical investigations on the unit cell can provide efficient guidelines for the design of overall core structures for a specific application. When any types of external forces are applied on the sandwich panel, each truss member of the unit cell undergoes severe plastic deformation without any restrictions so that the deformation behavior is strongly dependent on mesh density and element type. Therefore, in order to improve simulation accuracy and minimize calculation time, it is necessary to investigate the influence of element type and mesh density on that. In this work, as the preparatory stage to predict the mechanical behavior of a pyramidal unit cell, a series of finite element simulations for various element sizes and types were carried out. The influence of mesh density and element type on the simulation accuracy was investigated in diverse aspects; calculation time, resultant load, deformed geometry, effective modulus and peak stress.

Oxygen-deficiency-induced 6H-polymorph of hexagonal perovskite Ba4YMn3O11.5−δ: synthesis, structure and properties

The 12-layer hexagonal perovskite Ba4YMn3O11.5 (Rm, referred to as 12R) was transformed to a 6-layer mixed valent Mn3+/4+ hexagonal perovskite Ba4YMn3O10.7 (P63/mmc, referred to as 6H) via a partial-reduction in a N2 flow. This phase transformation between the 12R and 6H phases is redox-reversible. In contrast with the 12R-type Ba4YMn3O11.5 structure containing c-BaO2.75 and h-BaO3 layers with a (cchh)3 stacking, the 6H-type Ba4YMn3O10.7 structure consists of the cubic (c) BaO2.87 and hexagonal (h) BaO2.33 layers with a (cch)2 stacking, showing a preference of oxygen vacancy distribution in the hexagonal layers over the cubic layers. The h-BaO2.33 layer in the 6H-type Ba4YMn3O10.7 transforms two-thirds of face-sharing octahedral Mn2O9 dimers into edge-sharing pyramidal Mn2O8 units, sharing corners with Y octahedra/pyramids. Impedance measurements suggested that the 6H-type material is insulating with a bulk electrical resistivity of ∼107 Ω cm at 303 K, significantly higher than that for the 12R-type Ba4YMn3O11.5 by ∼4 orders of magnitude.

Distribution of tellurite polymorphs in the xM2O–(1 − x)TeO2 (M = Li, Na, K, Cs, and Rb) binary glasses using Raman spectroscopy

Raman spectra of xM2O–(1−x)TeO2 (M=alkali metal atom) binary glass-forming oxide systems were measured over a wide composition range and for all alkali-types in an effort to extend the structural aspects of previous works on this field and reveal the composition- and modifier type-induced structural changes in a quantitative manner for the first time. Analysis of the Raman spectroscopic data after a reduction procedure and focusing on spectral effects caused by structural changes allowed the “quantitative” monitoring of the well-known transformation of the TeO4 (predominating in the low modifier content glass) into TeO3 trigonal pyramids at increased alkali content. The main finding pertains to the estimation of the relative populations of the basic building blocks for a wide compositional range and for different alkali-types directly from the Raman spectroscopic data, thereby permitting the calculation of the average number around Te atoms versus modifier content and alkali-type. The variation of the coordination number implies that the structure of all M2O–TeO2 tellurite glasses with the same composition is comparable and almost independent of alkali-type.Spectroscopic evidence suggests that the presence of neutral trigonal pyramid TeO2/2(O) units is questionable, while the increase of M2O content leads to a gradual transformation of TeO4/2 initially to TeO3/2O− and then to TeO1/2O−(O) trigonal pyramid units depending on the modifier content. The structural model based on Raman spectroscopic results is in agreement with the findings of NMR work on binary alkali–tellurite glasses.

Synthesis, crystal structures, and optical properties of NaCd PnS 3 ( Pn = As, Sb)

Two compounds NaCd PnS 3 ( Pn = As ( 1), Sb ( 2)) were synthesized as transparent yellow and red platelets by reacting cadmium powder with the molten mixtures of Na 2S/As 2S 3/S and Na 2S/Sb/S at 500 °C. Both compounds are plagued with crystal twinning and acceptable crystal structure refinement could only be obtained by identifying the type of the twinning laws. NaCdAsS 3 ( 1) crystallizes in the monoclinic space group P2 1/ n (no. 14) with a = 5.6561(8), b = 16.5487(15), c = 5.6954(8) Å, β = 90.315(11)°, and Z = 4. NaCdSbS 3 ( 2) crystallizes in the monoclinic space group C2/ c (no. 15) with a = 8.1329(6), b = 8.1296(4), c = 17.2600(13) Å, β = 103.499(6)°, and Z = 8. The structures of both compounds feature a 2 ∞[Cd PnS 3] − layer composed of [CdS 4] tetrahedra and [AsS 3] or [SbS 3] pyramidal units. Between the 2 ∞[Cd PnS 3] − ( Pn = As, Sb) layers the Na + cations reside in a distorted octahedral environment of S atoms. Compound 1 is characterized with UV/Vis diffuse reflectance spectroscopy and IR and Raman spectra.

Heterobimetallic Copper(II) Uranyl Carboxyphenylphosphonates

The hydrothermal reactions of uranyl nitrate with diethyl(2-ethoxycarbonylphenyl)phosphonate, 3-carboxyphenylphosphonic acid, or diethyl(3-ethoxycarbonylphenyl)phosphonate with HF result in the formation of [Cu(H2O)]2Cu(H2O)2[(UO2)(PO3C6H4CO2H)(PO3C6H4CO2)]2 (UCuCPPE-1) and [H3O]2[Cu(H2O)]2[(UO2)3(PO3C6H4CO2)4]·3H2O (UCuCPPE-2). UCuCPPE-1 is constructed from the UO22+ moiety coordinated by four additional oxygen donor atoms from the phosphonate moiety, resulting in a tetragonal bipyramidal geometry. The phosphonate groups span between the uranyl cations to create chains that are in turn linked into sheets by square planar and square pyramidal Cu(II) units. The phenyl groups separate the sheets from one another. The structure of UCuCPPE-2 consists of a three-dimensional network of tetragonal bipyramidal and pentagonal bipyramidal U(VI) centers. These units form chains that the phosphonate groups link into sheets. The sheets are then joined together by square pyramidal CuO5 units to create the three-dimensi...