Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Topology

  • different topology
  • dna topology
  • molecular topology
  • network topology
  • new topology
  • similar topology
  • tree topology

  • Terms modified by Topology

  • topology design
  • topology optimization

  • Selected Abstracts

    Progressive Simplification of Tetrahedral Meshes Preserving All Isosurface Topologies

    Yi-Jen Chiang
    In this paper, we propose a novel technique for constructing multiple levels of a tetrahedral volume dataset whilepreserving the topologies of all isosurfaces embedded in the data. Our simplification technique has two majorphases. In the segmentation phase, we segment the volume data into topological-equivalence regions, that is, thesub-volumes within each of which all isosurfaces have the same topology. In the simplification phase, we simplifyeach topological-equivalence region independently, one by one, by collapsing edges from the smallest to the largesterrors (within the user-specified error tolerance, for a given error metrics), and ensure that we do not collapseedges that may cause an isosurface-topology change. We also avoid creating a tetrahedral cell of negative volume(i.e., avoid the fold-over problem). In this way, we guarantee to preserve all isosurface topologies in the entiresimplification process, with a controlled geometric error bound. Our method also involves several additionalnovel ideas, including using the Morse theory and the implicit fully augmented contour tree, identifying typesof edges that are not allowed to be collapsed, and developing efficient techniques to avoid many unnecessary orexpensive checkings, all in an integrated manner. The experiments show that all the resulting isosurfaces preservethe topologies, and have good accuracies in their geometric shapes. Moreover, we obtain nice data-reductionrates, with competitively fast running times. [source]

    Isotropic "Islands" in a Cholesteric "Sea": Patterned Thermal Expansion for Responsive Surface Topologies,

    ADVANCED MATERIALS, Issue 14 2006
    E. Sousa
    A method to capture ordered and disordered regions in reactive mesogen films to take advantage of the anisotropic thermal properties and fabricate a thermally responsive patterned film is presented. The image shows white-light interferometer images of isotropic cylinders in cholesteric material. The underlying principle phenomenon observed here is well described by a finite-element simulation. [source]

    Anatase and Rutile TiO2 Macrocellular Foams: Air,Liquid Foaming Sol,Gel Process Towards Controlling Cell Sizes, Morphologies, and Topologies,

    ADVANCED MATERIALS, Issue 1 2005
    F. Carn
    Titania foams (see Figure) can be produced using a non-static air,liquid foaming sol,gel process where nitrogen is bubbled through a mixture of a surfactant and a sol,gel precursor. Either anatase or rutile phase mesoporous titania foams are produced upon thermal treatment. Macroscopic cell morphologies can be tuned by changing the air-to-liquid-foam ratios and the size of the nitrogen bubbles, while wall topologies can be varied by changing surfactant. [source]

    Optimization of Network Topologies for Service Providers in the Telecommunications Market

    Dieter B. Pressmar
    Following the deregulation of communications services, a growing number of commercial providers are offering global voice and data communications services via rented infrastructures. These service providers are faced with the challenge to determine cost-effective network-topologies, considering both the variety of contractual arrangements with national and international network providers, and the communication profiles of their customers. This paper introduces a planning model for solving the optimization problem outlined above. The model is evaluated on the basis of mixed-integer optimization. Practical deployment of this approach is discussed with respect to the run-time characteristics of the MIP solvers. Subsequently, a genetic algorithm is applied to the model and the results are compared to those of the mixed-integer optimization. [source]

    Molecular systematics of cowries (Gastropoda: Cypraeidae) and diversification patterns in the tropics

    This study produces a nearly comprehensive phylogeny for the marine gastropod group Cypraeidae (cowries) and uses this topology to examine diversification patterns in the tropics. The dataset is based on molecular sequence data from two mitochondrial genes and includes 210 evolutionary significant units (ESUs) from 170 recognized species (>80%). Systematics for the group is revised based on well-supported clades, and tree topology is generally consistent with previously proposed classification schemes. Three new genera are introduced (Cryptocypraea gen. nov, Palmulacypraea gen. nov, and Contradusta gen. nov) and two previous genera are resurrected (Perisserosa and Eclogavena). One new tribe is proposed (Bistolidini). Topologies produced by a range of transition:transversion (Ti:Tv) weighting schemes in parsimony are pooled and evaluated using maximum likelihood criteria. Extensive geographical coverage shows persistent, large-scale geographical structure in sister-groups. Genetic divergence between subspecies is often equivalent or even greater than that between recognized species. Using ESUs as a metric, diversity throughout the Indo-West Pacific (IWP) increases by 38%. Intra- and inter-regional diversification patterns show that the IWP is the centre for speciation in cowries. The other major tropical regions of the world are inhabited by a predominantly relictual fauna; from a cowrie's eye-view. Good dispersal ability begets larger ranges, increased extinction resistance and morphological stasis; whereas shorter larval duration results in smaller ranges, higher speciation rates, but also higher turnover. Larval duration and dispersal ability appear correlated with ocean productivity as taxa with longer-lived larvae are associated with oligotrophic conditions; whereas taxa with shorter larval durations are associated with eutrophic, continental conditions. This tendency is carried to the extreme in temperate or upwelling regions where a planktonic phase is completely lost and crawl-away larvae evolve multiple times. A strong phylogenetic trend supports these observations as lineages leading up to and including the derived Indo-West Pacific Erroneinae clade contain taxa predominantly restricted to continental habitats and have undergone the greatest evolutionary radiations in their respective regions. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 79, 401, 459. [source]

    Hydrothermal Preparation of Nickel(II)/Uranium(IV) Fluorides with One-, Two-, and Three-Dimensional Topologies.

    CHEMINFORM, Issue 28 2003
    Amanda C. Bean
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]

    Molecules with New Topologies Derived from Hydrogen-Bonded Dimers of Tetraurea Calix[4]arenes

    Anca Bogdan Dr.
    Abstract Tetraurea calix[4]arenes 2 have been synthesized in which two adjacent aryl urea residues are connected to a loop by an aliphatic chain -O-(CH2)n -O-. The remaining urea residues have a bulky 3,5-di- tert -butylphenyl residue and an , -alkenyloxyphenyl residue. Since this bulky residue cannot pass through the loop, only one homodimer (2,2) is formed in apolar solvents, for steric reasons, in which the two alkenyl residues penetrate the two macrocyclic loops. Covalent connection of these alkenyl groups by olefin metathesis followed by hydrogenation creates compounds 3, which consist of molecules with hitherto unknown topology. Their molecular structure was confirmed by 1H,NMR spectroscopy and ESIMS, and for one example by single-crystal X-ray analysis. [source]

    Utilization of Self-Sorting Processes To Generate Dynamic Combinatorial Libraries with New Network Topologies

    Isabelle Saur Dr.
    Abstract The synthesis of water-soluble, organometallic macrocycles is described. They were obtained by self-assembly in reactions of the half-sandwich complexes [{Ru(C6H5Me)Cl2}2], [{Ru(p -cymene)Cl2}2], [{Rh(Cp)Cl2}2], and [{Ir(Cp*)Cl2}2] with the ligand 5-dimethylaminomethyl-3-hydroxy-2-methyl-4-(1H)-pyridone in buffered aqueous solution at pH 8. The structure of the Ru,(p -cymene) complex was determined by single-crystal X-ray crystallography. Upon mixing, these complexes undergo scrambling reactions to give dynamic combinatorial libraries. In combination with structurally related complexes based on amino-methylated 3-hydroxy-2-(1H)-pyridone ligands, an exchange of metal fragments but no mixing of ligands was observed. This self-sorting behavior was used to construct dynamic combinatorial libraries of macrocycles, in which two four-component sub-libraries are connected by two common building blocks. This type of network topology influences the adaptive behavior of the library as demonstrated in selection experiments with lithium ions as the target. [source]

    A Hierarchical Topology-Based Model for Handling Complex Indoor Scenes

    D. Fradin
    Abstract This paper presents a topology-based representation dedicated to complex indoor scenes. It accounts for memory management and performances during modelling, visualization and lighting simulation. We propose to enlarge a topological model (called generalized maps) with multipartition and hierarchy. Multipartition allows the user to group objects together according to semantics. Hierarchy provides a coarse-to-fine description of the environment. The topological model we propose has been used for devising a modeller prototype and generating efficient data structure in the context of visualization, global illumination and 1 GHz wave propagation simulation. We presently handle buildings composed of up to one billion triangles. [source]

    Synthesis, Upconversion Luminescence and Magnetic Properties of New Lanthanide,Organic Frameworks with (43)2(46,66,83) Topology

    Danfeng Weng
    Abstract The synthesis and crystal structures of three new lanthanide,organic frameworks [Ln(pza)(OH)(H2O)]n (Ln = Y(1), Er(2), Yb(3); H2pza = 2,3-pyrazinedicarboxylic acid) with helical chains and novel 2D (43)2(46,66,83) topology are reported. The topology is obtained by simplifying the dinuclear metal core as a six-connected node and the ligand as a three-connected linker. The upconversion property measurement gives green and red emissions coming from two-photon excitation of Y: Er, Yb codoped coordination polymer and arising from ErIII transitions of 4S3/2/2H11/2,4I15/2 and 4F9/2,4I15/2. The magnetic properties of complexes 2 and 3 are also studied.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Preparation and Molecular Structures of Stable Bis(germylenes) with Pincer Topology

    F. Ekkehardt Hahn
    Abstract Benzannulated N-heterocyclic bis(germylenes) with pincer ligand topology have been prepared by the reaction of N,N,,N,,N,, -tetralithiated tetraamines with GeCl2·1,4-dioxane or by the transamination reaction between a tetraamine and Ge[N(SiMe3)2]2. X-ray diffraction studies have shown, that the bis(germylenes) exist as monomers in the solid state. Significant intramolecular Ge···Ge and Ge···N interactions have been observed for the lutidine-bridged bis(germylene). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Topology and Dependency Tests in Spatial and Network Autoregressive Models

    Steven Farber
    Social network analysis has been identified as a promising direction for further applications of spatial statistical and econometric models. The type of network analysis envisioned is formally identical to the analysis of geographical systems, in that both involve the measurement of dependence between observations connected by edges that constitute a system. An important item, which has not been investigated in this context, is the potential relationship between the topology properties of networks (or network descriptions of geographical systems) and the properties of spatial models and tests. The objective of this article is to investigate, within a simulation setting, the ability of spatial dependency tests to identify a spatial/network autoregressive model when two network topology measures, namely degree distribution and clustering, are controlled. Drawing on a large data set of synthetically controlled social networks, the impact of network topology on dependency tests is investigated under a hierarchy of topology factors, sample size, and autocorrelation strength. In addition, topology factors are related to known properties of empirical systems. El análisis de redes sociales ha sido y es una dirección prometedora en el avance de las aplicaciones de modelos econométricos y de estadística espacial. El tipo de análisis de redes que proponemos es idéntico al análisis de sistemas geográficos, ya que ambos miden la dependencia entre observaciones conectadas que conforman un sistema. Un punto importante que no ha sido investigado en este contexto es la potencial relación entre las propiedades topológicas de redes (o descripción de redes de sistemas geográficos) y las propiedades de los modelos y pruebas (tests) espaciales. El objetivo de este artículo es investigar (dentro del marco de simulaciones Monte Carlo), la capacidad que poseen las pruebas de dependencia espacial para identificar un modelo autorregresivo espacial/de redes, en los casos en los que dos medidas topológicas de redes (grado de distribución y transitividad) son controlados. Haciendo uso de una base de datos de redes sociales controladas sintéticamente, este artículo evalúa el impacto de la topología de redes en las pruebas de dependencia espacial. Dicho impacto es evaluado con respecto a variaciones en los factores topológicos, el tamaño de muestra, y los niveles de autocorrelación espacial. Adicionalmente, los factores topológicos son relacionados a propiedades conocidas de varios sistemas empíricos. [source]

    Models of Earth's main magnetic field incorporating flux and radial vorticity constraints

    A. Jackson
    SUMMARY We describe a new technique for implementing the constraints on magnetic fields arising from two hypotheses about the fluid core of the Earth, namely the frozen-flux hypothesis and the hypothesis that the core is in magnetostrophic force balance with negligible leakage of current into the mantle. These hypotheses lead to time-independence of the integrated flux through certain ,null-flux patches' on the core surface, and to time-independence of their radial vorticity. Although the frozen-flux hypothesis has received attention before, constraining the radial vorticity has not previously been attempted. We describe a parametrization and an algorithm for preserving topology of radial magnetic fields at the core surface while allowing morphological changes. The parametrization is a spherical triangle tesselation of the core surface. Topology with respect to a reference model (based on data from the Oersted satellite) is preserved as models at different epochs are perturbed to optimize the fit to the data; the topology preservation is achieved by the imposition of inequality constraints on the model, and the optimization at each iteration is cast as a bounded value least-squares problem. For epochs 2000, 1980, 1945, 1915 and 1882 we are able to produce models of the core field which are consistent with flux and radial vorticity conservation, thus providing no observational evidence for the failure of the underlying assumptions. These models are a step towards the production of models which are optimal for the retrieval of frozen-flux velocity fields at the core surface. [source]

    Topology of the Mitochondrial Inner Membrane: Dynamics and Bioenergetic Implications

    IUBMB LIFE, Issue 3-5 2001
    Carmen A. Mannella
    Abstract Electron tomography indicates that the mitochondrial inner membrane is not normally comprised of baffle-like folds as depicted in textbooks. In actuality, this membrane is pleomorphic, with narrow tubular regions connecting the internal compartments (cristae) to each other and to the membrane periphery. The membrane topologies observed in condensed (matrix contracted) and orthodox (matrix expanded) mitochondria cannot be interconverted by passive folding and unfolding. Instead, transitions between these morphological states likely involve membrane fusion and fission. Formation of tubular junctions in the inner membrane appears to be energetically favored, because they form spontaneously in yeast mitochondria following large-amplitude swelling and recontraction. However, aberrant, unattached, vesicular cristae are also observed in these mitochondria, suggesting that formation of cristae junctions depends on factors (such as the distribution of key proteins and/or lipids) that are disrupted during extreme swelling. Computer modeling studies using the "Virtual Cell" program suggest that the shape of the inner membrane can influence mitochondrial function. Simulations indicate that narrow cristae junctions restrict diffusion between intracristal and external compartments, causing depletion of ADP and decreased ATP output inside the cristae. [source]

    Symbolic Inversion, the Topology of El Mestizaje, and the Spaces of Las Razasin Ecuador

    Norman E. Whitten Jr.Article first published online: 28 JUN 200
    La met´fora de la topología étnica se presta para una discusión de las inversiones simbólicas que cuestionan las dimensiones dominantes de la ideología hegemónica del mestizaje, la mezcla de un cuerpo social nacional de ecuatorianos. El enfoque está sobre espacios sociopoliticos selectos donde los conceptos de la raza sobresalen en ciertos contextos y escenarios. El mestizaje ideológico y sus multiples inversiones estín vinculados con los cambios en el poder estructural que nacen de la acción social motivada por el simbolismo. La din´mica de las inversiones simbólicas es fundamental para la política y la poe'tica de la identidad local que contribuyen a la tranformación de las representaciones colectivas. Estas representaciones, a la vez, pueden motivar a los movimientos sociales. Este artículo explica los contrastes entre los metatropos del mestizaje y del multiculturalismo. [source]

    Topology and patch-clamp analysis of the sodium channel in relationship to the anti-lipid a antibody in campylobacteriosis

    Seigo Usuki
    Abstract An infecting strain VLA2/18 of Campylobacter jejuni was obtained from an individual with campylobacteriosis and used to prepare chicken sera by experimental infection to investigate the role of serum anti-ganglioside antibodies in Guillain-Barré syndrome. Both sera of the patient and chicken contained anti-ganglioside antibodies and anti-Lipid A (anti-Kdo2-Lipid A) antibodies directed against the lipid A portion of the bacterial lipooligosaccharide. The anti-Kdo2-Lipid A activities inhibited voltage-gated Na (Nav) channel of NSC-34 cells in culture. We hypothesized that anti-Kdo2-Lipid A antibody acts on the functional inhibition of Nav1.4. To test this possibility, a rabbit peptide antibody (anti-Nav1.4 pAb) against a 19-mer peptide (KELKDNHILNHVGLTDGPR) on the , subunit of Nav1.4 was produced. Anti-Nav1.4 pAb was cross-reactive to Kdo2-Lipid A. Anti-Kdo2-lipid A antibody activity in the chicken serum was tested for the Na+ current inhibition in NSC-34 cells in combination with ,-Conotoxin and tetrodotoxin. Contrary to our expectations, the anti-Kdo2-Lipid A antibody activity was extended to Nav channels other than Nav1.4. By overlapping structural analysis, it was found that there might be multiple peptide epitopes containing certain dipeptides showing a structural similarity with v-Lipid A. Thus, our study suggests the possibility that there are multiple epitopic peptides on the extracellular domains of Nav1.1 to 1.9, and some of them may represent target sites for anti-Kdo2-Lipid A antibody, to induce neurophysiological changes in GBS by disrupting the normal function of the Nav channels. © 2008 Wiley-Liss, Inc. [source]


    Article first published online: 24 SEP 200
    Zimmermann, S. & Triemer, R. E. Department of Life Sciences, Rutgers University, Piscataway, NJ 08854 USA The phylogeny of the Euglenophytes has previously been examined using the SSU rDNA. Results from these analyses indicated that the phototrophic genera are not monophyletic. To test this hypothesis, a second gene was sequenced, the LSU rDNA. The taxa used in this study were selected from clades represented in the SSU analyses so that comparisons could be made between gene phylogenies and a combined dataset could be created. Conserved areas of the aligned sequences for both the LSU and SSU were used to generate parsimony, maximum likelihood, and distance trees. Topology of the SSU and LSU trees was similar. The SSU and LSU data consistently generated the same four highly supported terminal clades and varied only in the placement of Euglena stellata and Euglena viridis. The internal nodes of the SSU trees were weakly supported, whereas the LSU provided higher support for these nodes. A combined LSU and SSU dataset was then created. Analysis of the combined dataset yielded trees with identical topologies to those found in the individual datasets and demonstrated strong support for the four terminal clades. These results show that phylogeny of the Euglenophytes as inferred previously from SSU data is confirmed by the LSU data and that the LSU rDNA gene may be useful in elucidating relationships among the major clades. [source]

    FIB-Nanotomography of Particulate Systems,Part I: Particle Shape and Topology of Interfaces

    Lorenz Holzer
    A new 3D-microscopy method, focused ion beam-nanotomography (FIB-nt), has been applied to the statistical particle shape analysis and for topological characterization of granular textures in cement samples. Because of its high resolution (15 nm), FIB-nt reveals precise microstructural information at the submicrometer scale, which cannot be obtained with conventional tomography methods. It is demonstrated that even from complex granular textures with dense agglomerates, it is possible to identify the individual sub-grains. This is the basis for reliable statistical shape analysis. For this purpose, moments of inertia were determined for particles from five different grain size fractions of a given cement, which provides important input data for future modeling of rheology and hydration processes. In addition, FIB-nt was used for topological characterization of the particle,particle interfaces in the dense and fine-grained granular textures. The unique 3D-data obtained with FIB-nt thus open new possibilities for quantitative microstructure analysis and the data can be used as structural input for object-oriented modeling. [source]

    Cages with Tetrahedron-Like Topology Formed from the Combination of Cyclotricatechylene Ligands with Metal Cations,

    ANGEWANDTE CHEMIE, Issue 16 2010
    Viel Platz: Anionische tetraedrische Aggregate, gebildet durch Kombination von Cyclotricatechylen-Anionen mit Übergangsmetallionen wie Vanadium (siehe Bild), umschließen große Hohlräume, die Alkalimetallionen und Lösungsmittelmoleküle aufnehmen können. Anionische Einheiten mit geeigneten Metallzentren lassen sich zu hoch symmetrischen Koordinationspolymeren verknüpfen (V,blau, O,rot, C,schwarz). [source]

    Design of a G-Quadruplex Topology through Glycosidic Bond Angles,

    ANGEWANDTE CHEMIE, Issue 48 2009
    Mateus Webba, Silva Dr.
    Baugenehmigung: Bisher wurden neuartige DNA-Quadruplextopologien durch Zufall entdeckt. Mit dem hier vorgestellten System lassen sich nun auf der Grundlage des Winkels der Glycosidbindung von Guanosinen einige Regeln ableiten, um Quadruplextopologien vorherzusagen. Die Methode wurde auf bekannte Strukturen angewendet und genutzt, um neue selbstorganisierte DNA-Quadruplexe zu erhalten. [source]

    A General Synthetic Approach to Interconnected Nanowire/Nanotube and Nanotube/Nanowire/Nanotube Heterojunctions with Branched Topology,

    ANGEWANDTE CHEMIE, Issue 39 2009
    Guowen Meng Prof.
    Ein kombinatorisches Verfahren macht eine breite Vielfalt von Nanodraht/Nanoröhren(NW/NT)- und Nanoröhren/Nanodraht/Nanoröhren(NT/NW/NT)-Architekturen mit Verzweigungstopologie zugänglich. Die Nanodrähte werden durch Elektroabscheidung in den verzweigten Kanälen anodischer Aluminiumoxidtemplate erzeugt und selektiv geätzt, anschließend werden in den leeren Kanälen Nanoröhren an die Nanodraht-Enden gezüchtet. [source]

    Network Topology of a Hybrid Organic Zinc Phosphate with Bimodal Porosity and Hydrogen Adsorption,

    ANGEWANDTE CHEMIE, Issue 33 2009
    Shu-Hao Huang
    Füll,s auf! Ein nanoporöses hybrides Zinkphosphat (siehe Bild; ,[Zn2PO4]-Säulen in Dunkelblau) mit in die Struktur integrierten organischen Liganden (Amin: grau; Arylcarboxylat: cyan) weist eine ungewöhnliche bimodale Porosität und Wasserstoffgas-Speicherfähigkeit auf. [source]

    I,Time, Topology and Physical Geometry

    Tim Maudlin
    The standard mathematical account of the sub-metrical geometry of a space employs topology, whose foundational concept is the open set. This proves to be an unhappy choice for discrete spaces, and offers no insight into the physical origin of geometrical structure. I outline an alternative, the Theory of Linear Structures, whose foundational concept is the line. Application to Relativistic space-time reveals that the whole geometry of space-time derives from temporal structure. In this sense, instead of spatializing time, Relativity temporalizes space. [source]

    ChemInform Abstract: Comparative Studies on the Phase Stability, Electronic Structure, and Topology of the Charge Density in the Li3XO4 (X: P, As, V) Lithium Orthosalt Polymorphs

    CHEMINFORM, Issue 31 2009
    Christine Frayret
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    ChemInform Abstract: Remote Induction of Asymmetry in [13]-Macro-dilactone Topology by a Single Stereogenic Center.

    CHEMINFORM, Issue 4 2009
    W. Sean Fyvie
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    ChemInform Abstract: Chromium-Doped Germanium Clusters CrGen (n = 1,5): Geometry, Electronic Structure, and Topology of Chemical Bonding

    CHEMINFORM, Issue 11 2008
    Xin-Juan Hou
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    ChemInform Abstract: Zeolite-Like Nitride,Chlorides with a Predicted Topology.

    CHEMINFORM, Issue 8 2008
    Andrew J. D. Barnes
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    (K4Li4) Al8Ge8O32×8H2O: An Li+ -Exchanged Potassium Aluminogermanate with the Zeolite Gismondine (GIS) Topology.

    CHEMINFORM, Issue 46 2003
    Aaron J. Celestian
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]

    Designed Topology and Site-Selective Metal Composition in Tetranuclear [MM,,,,M,M] Linear Complexes

    Abstract The ligand 1,3-bis[3-oxo-3-(2-hydroxyphenyl)propionyl]benzene (H4L), designed to align transition metals into tetranuclear linear molecules, reacts with MII salts (M=Ni, Co, Cu) to yield complexes with the expected [MM,,,MM] topology. The novel complexes [Co4L2(py)6] (2; py=pyridine) and [Na(py)2][Cu4L2(py)4](ClO4) (3) have been crystallographically characterised. The metal sites in complexes 2 and 3, together with previously characterised [Ni4L2(py)6] (1), favour different coordination geometries. These have been exploited for the deliberate synthesis of the heterometallic complex [Cu2Ni2L2(py)6] (4). Complexes 1, 2, 3 and 4 exhibit antiferromagnetic interactions between pairs of metals within each cluster, leading to S=0 spin ground states, except for the latter cluster, which features two quasi-independent S=1/2 moieties within the molecule. Complex 4 gathers the structural and physical conditions, thus allowing it to be considered as prototype of a two-qbit quantum gate. [source]

    Zn[BPO4(OH)2]: A Zinc Borophosphate with the Rare Moganite-Type Topology

    Ya-Xi Huang Dr.
    Abstract A novel zinc borophosphate Zn[BPO4(OH)2] with moganite-type topology (a rare polymorph of silica) has been prepared from a mixture of ZnO, B2O3, and P2O5 by hydrothermal treatment at 443,K. The crystal structure was determined from single-crystal X-ray data (orthorhombic, Pbcn (no. 60), a=915.07(3), b=897.22(3), c=1059.19(3),pm, V=869.62(5)×106,pm3, Z=8, R1=0.028, wR2=0.075). The crystal structure comprises unbranched vierer -single borophosphate chains running along [010] and interconnected via ZnO2(OH)2 -tetrahedra by sharing common vertices. The resulting topology of the three-dimensional tetrahedral framework structure is described by the Schläfli symbol (42.62.82)(4.64.8)2. Although showing Zn in a tetrahedral coordination, the title compound does not belong to the group of zincoborophosphates but is a special case of a borophosphate containing vierer single rings of tetrahedra with the sequence Zn-B-Zn-P. [source]