1,721,324 research outputs found
Homochiral transition-metal camphorate coordination architectures containing "piperazine-pyridine" ligands
No full text[[abstract]]A total of five homochiral metal-organic coordination polymers (MOCPs) showing high thermal stability have been assembled from the reaction of divalent transition-metal ions (Co(2+), Zn(2+), and Cd(2+)), rigid enantiopure D-camphoric acid (D-H(2)Cam), and achiral neutral N,N'-bis(pyrid-4-yl) piperazine (bpypip) ligand under hydro(solvo)thermal conditions. Compound [Co(2)(D-Cam)(2)(bpypip)] (1) features a chiral-layered cobalt-camphorate coordination (4,4)-net, which is pillared by auxiliary linear N-tethering bpypip linkers to yield a homochiral three-dimensional coordination framework with Schlafli symbol of 4(4).6(10).8. Compounds [M(D-HCam)(2)(bpypip)] (2, M = Cd; 3, M = Zn) have nearly identical one-dimensional M-bpypip zigzag coordination-chain structures, in which each metal ion further attaches to two partially deprotonated monoanionic D-HCam terminals, which exhibit two types of partially deprotonating manner in 2 but only one type in 3. Through chain-to-chain C(= O)OH center dot center dot center dot O(carboxylate) hydrogen bonds, the zigzag coordination-chain becomes extended to a three-dimensional uninodal 6-connected supramolecular network, which can be considered as a result of a M-D-HCam-based 4-connected supramolecular 6(5).8-net intersected by M-bpypip-based zigzag coordination-chains. Of particular interest, the supramolecular assembly contains a couple of single-stranded right- (SRH) and left-handed (SLH) supramolecular helices and a couple of double-stranded right-(DRH) and left-handed (DLH) supramolecular helices, and therefore exists as a meso-net in topology, i.e., there is no spatial chirality. Compounds [M(2)(OH)(OAc)(D-Cam)(bpypip)] (4, M = Co; 5, M = Zn) have identically homochiral ladder-like chain structures having meso-M2 units and presenting three kinds of different anions, i.e., hydroxyl, acetate, and D-Cam. The obtained acetate anion may be generated from the hydrolyzation of dimethylacetamide (DMAc) under hydro(solvo) thermal conditions.[[note]]SC
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Discrete and Infinite Metallacyclic Coordination Architectures Based on a Conformationally Flexible Tripodal Aminotriazine-Derived Polypyridyl Ligand
No full text[[abstract]]A novel tripodal semi-rigid ligand, 2,4,6-tris(3-picolylamino)-1,3,5-triazine (m-H(3)tpat), consisting of a triazine central core and three pyridine donating functions attached to flexible NHCH2- arms has been designed and synthesized. The self-assembly reactions of m-H(3)tpat with copper(II) chloride and cobalt(II) chloride yielded discrete Cu-II complex [Cu2Cl4(m-H(3)tpat)(2)]center dot 2H(2)O center dot 2EtOH (1 center dot 2H(2)O center dot 2EtOH) and polymeric Co-II complex [Co(m-H(3)tpat)(2)(H2O)(2)]Cl-2 (2), respectively. Complex 1 has a metallacyclophane structure with a metal-to-ligand ratio of 2:2. Each copper(II) ion adopts a pentacoordinate square-pyramidal geometry with a N3Cl2 coordination sphere. Complex 2 exhibits an extended chain structure based on {Co-2(m-H(3)tpat)(2)} metallacyclic repeating units. Each cobalt(II) ion adopts a hexacoordinate octahedral geometry with a N2O4 coordination environment. Note that the m-H(3)tpat ligand exists in a cis-cis-cis conformation in 1 and a cis-trans-trans conformation in 2, with the central aminotriazine moiety appearing to be an asymmetric-configured allamino tautomer in both conformers. The stabilities of the two coordination-directed structures may be enhanced by intramolecular p-p interactions between two pyridine rings from two different m-H(3)tpat ligands within the metallacyclophane structure of 1 and by a set of complementary double hydrogen bonds (DA-AD arrays) between two aminotriazine moieties of two m-H(3)tpat ligands within a metallacyclic unit for 2.[[note]]SC
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Giant metal-organic frameworks with bulky scaffolds: from microporous to mesoporous functional materials
No full text[[abstract]]New concepts on the design and synthesis of crystalline metal-organic frameworks (MOFs) have made them a subject of considerable interest in the growing field of materials science. By creating larger cavity sizes by a nearly infinite combination of metal nodes and organic linkers, many innovative characteristics of microporous MOFs have been revealed. The primary goal of this perspective article is to highlight the frontiers in the development of giant MOFs that are deliberately constructed from metallated or metal-free bulky scaffolds. Incorporating these types of distinct bulky ligands into giant MOFs may lead to MOFs with a large cavity size, intriguing properties and new framework topology. Emerging applications of these materials in catalysis, adsorption, and sensors are also discussed.[[note]]SC
Ligand dissociation/recoordination in fluorescent ionic zinc-salicylideneimine compounds: synthesis, characterization, photophysical properties, and H-1 NMR studies
No full text[[abstract]]A series of ionic zinc-salicylideneimine compounds, [HNEt3][Zn(L)Cl-2] (L = sal(H)-4-CN, 1; sal(Cl)-4-CN, 2; sal(Br)-4-CN, 3; sal(OMe)-4-CN, 4) and [NEt4][Zn(sal(H)-4-CN)Cl-2] (5), have been synthesized and structurally characterized. Compounds 1-5 all display an intense fluorescence band in both solution (methanol, MeOH; acetonitrile, ACN; dimethylsulfoxide, DMSO; dichloromethane, DCM) and solid phases, with a maximum in the region of 515-560 nm and 529-573 nm, respectively. Detailed H-1 NMR and optical spectroscopic studies indicate the occurrence of ligand dissociation and recoordination in 1-4 in solution, leading to an equilibrium between the zinc-salicylideneimine complex species, [Zn(L)Cl-2](-), and the salicylideneimine free ligand, HL. The tendency of ligand dissociation is related to the solvent, the concentration, and the substitution of the salicylidene ring. The greatest degree of ligand dissociation is observed for 1-4 when dissolved in noncoordinating, less polar DCM solvent, followed by coordinating, high polar DMSO solvent. The least degree of ligand dissociation occurs in solutions of coordinating, moderately polar MeOH and ACN solvents for 1-3 and 4, respectively. Dilute solutions are likely characterized by the high degree of ligand dissociation, whereas the equilibrium shifts in favor of the complex [Zn(L)Cl-2](-) form at higher concentration. Furthermore, the electron-donating methoxy substitution in the salicylidene ring promotes a high tendency for ligand dissociation, while electron-withdrawing chloro and bromo groups cause the reverse tendency. The H-1 NMR spectrum of 5 shows only one set of proton resonances in the aromatic region corresponding to the complex [Zn(sal(H)-4-CN)Cl-2](-) species, indicating that the lack of ammonium proton would protect the complex form from ligand dissociation.[[note]]SC
Influence of Counteranions on the Structural Modulation of Silver-Di(3-pyridylmethyl)amine Coordination Polymers
No full text[[abstract]]The coordination chemistry of a flexible N-donor ligand di(3-pyridylmethyl)amine (dpma) with silver salts has been investigated. Six new silver coordination polymers, namely, [Ag(dpma)(H2O)](NO3) (1), [Ag(dpma)-(CF3CO2)]center dot 1/2H(2)O (2), [Ag(dpma)](CF3SO3)]center dot 1/2H(2)O (3), [Ag(dpma)](BF4)center dot 3/2H(2)O (4), [Ag-3(dpma)(2)(H2O)](ClO4)(3) (5), and [Ag(dpma)](PF6) (6), have been prepared by slow diffusion reactions. All the polymeric structures of compounds 1-6 are described as topologic binodal networks in terms of Ag and dpma building blocks. Compounds 1-4 show a one-dimensional ladder-like chain structure, with both Ag and dpma as three-connected T-nodes; compound 5 is an uncommon one-dimensional metallamacrocycle-based chain structure, with Ag as two-connected I-node and dpma as three- connected T-node; compound 6 is a two-dimensional honeycomb-like layer structure, with both Ag and dpma as three-connected Y-nodes. Within the structures, the dpma ligand adopts a variety of structure conformations including gauche trans anti (1 and 2), trans-trans-anti (3 and 4), trans-trans-syn (3), gauche-gauche-syn (5), and trans-gauche-syn (6) conformations. For these Ag-dpma coordination polymers, the structural diversity and complexity are most likely attributed to the different coordinating nature, hydrogen-bonding propensity, and templating effect of the counteranions and solvent molecules. Solution studies suggest that compounds 1-6 would disaggregate to break down the polymeric structures and then to give multiple rapidly exchanging solution species in DMSO or acetonitrile. The thermal stabilities of compounds 1-6 are examined. In addition, the photoluminescent properties of compounds 1-6 are investigated in the solid state at room temperature.[[note]]SC
Hydro(solvo)thermal synthesis of homochiral metal-camphorate coordination polymers
No full text[[abstract]]Two thermally stable homochiral metal-camphorate coordination polymers, [Co(D-Cam)] (1) and [Cu(2)(D-Cam)(2)(D-H(2)Cam)(2)] (2), have been hydro(solvo) thermally synthesized from the reaction of D-camphoric acid (D-H(2)Cam) with the corresponding metal salts. Polymer 1 has a three-dimensional homochiral framework involving one-dimensional cobalt-carboxylate chains aligned parallel to the [100] direction. Polymer 2 features a homochiral-layered structure with grid-like (4,4)-topology, which extended to a three-dimensional supramolecular assembly through hydrogen-bonded cyclic R(2)(2)(8) patterned carboxylic acid dimers as supramolecular synthons. This supramolecular network appears to be self-penetrating and has a Schlafli symbol of 4(4)6(10)8. Magnetic studies revealed that polymer 1 exhibits possible antiferromagnetic couplings.[[note]]SC
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