1,721,027 research outputs found
The guest-dependent thermal response of the flexible MOF Zn2(BDC)2(DABCO)
No full textThe guest-dependent thermal response of the flexible MOF Zn2(BDC)2(DABCO) (1) has been studied. A series of temperature-dependent single crystallographic analyses revealed inherent structural thermal responses of 1. The guest-free framework 1 exhibited interesting thermal responses including anisotropic thermal expansion (negative thermal expansion (NTE) along the a- and b-axes, positive thermal expansion (PTE) along the c-axis) and disorder-order phase transition. In addition, inclusion of guest molecules (DMF and benzene) brought distinct thermal responses to 1 from host-guest interactions. 1·4DMF showed altered thermal responses, presenting disorder-order phase transitions at a higher temperature and PTE along the a- and b-axes. Meanwhile, 1·3benzene displayed a quite different type of thermal response such as a hinge like motion (breathing) without a symmetry change. © The Royal Society of Chemistry 2016114171sciescopu
A Palladium(II) Peroxido Complex Supported by the Smallest Steric N-Heterocyclic Carbene, IMe=1,3-Dimethylimidazole-2-ylidene, and Its Reactivity by Oxygen-Atom Transfer
No full textStabilized with an N-heterocyclic carbene ligand of the smallest steric profile, Pd-II(eta(2)-O-2)(IMe)(2) (IMe = 1,3-dimethylimidazole-2-ylidene) was synthesized by the direct addition of dioxygen to Pd-0(IMe)(2). The peroxidopalladium complex with IMe, which was previously available only by computation, was characterized by IR spectroscopy and X-ray crystallography. Moreover, its oxygen-atom-transfer reactivity was elucidated by studying its thermolysis in pyridine at 60 degrees C to yield 1,3-dimethylimidazol-2-one (IMeO) and its reaction with oxygen-atom-transfer acceptors such as PPh3 and (Me3Si)(2). © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei
Efficient synthesis of bulky N-Heterocyclic carbene ligands for coinage metal complexes
No full textA facile and efficient route to synthesize sterically bulky N-heterocyclic carbenes with high percent buried volumes has been developed. The method involves three steps from commercial reagents and produced the NHC precursors with approximately 40% overall yield without column chromatography. The free carbenes were isolated as confirmed by X-ray crystallography and 13C NMR peak at 213 ppm corresponding to the carbene carbons. The Cu(I), Ag(I), and Au(I) chloride complexes supported by the NHC ligands were successfully synthesized and fully characterized including X-ray crystallography. © 2016 Elsevier B.V1661sciescopu
Synthetic control of coincidental formation of an N-heterocyclic carbene-copper(i) complex and imidazolium cations within metal-organic frameworks
No full textBy changing the concentration of copper salt (Cu(ClO4)2), a two-dimensional (2D) copper paddle-wheel-based metal-organic framework (MOF) containing an imidazolium unit (Im-MOF-1 with a framework formula of [CuII(L)(NMP)](ClO4), L = 1,3-bis(4-carboxyphenyl)imidazolium and NMP = N-methyl-2-pyrrolidone) and a 3D MOF (Im-MOF-2, CuII(L)(H2O)) with aqua-bridged Cu ions as inorganic infinite secondary building units were respectively prepared. With CuCl as a copper source, another square-grid 2D MOF (Im-MOF-3, CuII(LNHC-CuICl)(NMP), LNHC = a carbene form of L) was obtained; Im-MOF-3 is isostructural with Im-MOF-1 except that its organic linker has an N-heterocyclic carbene (NHC) copper(i) complex (LNHC-CuICl). Density functional theory modeling calculations show that the NHC-CuCl complex in the organic linker of Im-MOF-3 retains the electronic properties of its molecular form, as evidenced by molecular orbital analysis. © The Royal Society of Chemistry1331sciescopu
Triazenyl Radicals Stabilized by N-Heterocyclic Carbenes
No full textNotwithstanding the notable progress in the synthesis of N-heterocyclic carbene-stabilized radicals, aminyl radicals, supported by NHCs or otherwise, have been scarcely studied due to synthetic challenges. Triazenyl radical is a particular form of aminyl radical that contains three adjacent nitrogen atoms, and offers intriguing possibilities for unique reactivity and physical properties stemming from expected delocalization of the spin density over the NNN moiety and its conjugated substituents. Here, we report the synthesis and full characterization of the first NHC-stabilized triazenyl radicals, obtained by one-electron reduction of the corresponding triazenyl cations with potassium metal. These radicals reversibly oxidize back to the cations upon treatment with transition metal sources or electrophiles, and abstract H atom from xanthene to form a new N - H bond at the center nitrogen atom. Potential application of the redox couple between triazenyl cation and triazenyl radical was demonstrated as cathode active materials in lithium ion batteries. © 2017 American Chemical Society1441sciescopu
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
How Does Solvation Affect the Binding of Hydrophilic Amino Saccharides to Cucurbit[7]uril with Exceptional Anomeric Selectivity?
No full textCucurbit[7]uril (CB[7]) is known to bind strongly to hydrophilic amino saccharide guests with exceptional aanomer selectivities under aqueous conditions. Single-crystal X-ray crystallography and computational methods were used to elucidate the reason behind this interesting phenomenon. The crystal structures of protonated galactosamine (GalN) and glucosamine (GluN) complexes confirm the inclusion of a anomers inside CB[7] and disclose the details of the host–guest binding. Whereas computed gas-phase structures agree with these crystal structures, gas-phase
binding free energies show preferences for the b-anomer complexes over their a counterparts, in striking contrast to the experimental results under aqueous conditions. However, when the solvation effect is considered, the binding structures drastically change and the preference for the a anomers is recovered. The a anomers also tend to bind more tightly and leave less space in the CB[7] cavity toward inclusion of only one water molecule, whereas loosely bound b anomers leave more space toward accommodating two water molecules, with markedly different hydrogenbonding natures. Surprisingly, entropy seems to contribute significantly to both anomeric discrimination and binding. This suggests that of all the driving factors for the strong complexation of the hydrophilic amino saccharide guests, water mediation plays a crucial role in the anomer discrimination. (c) 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim101sciescopu
Variations on the Author
Full text link“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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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