1,720,965 research outputs found
Tungsten's redox potential is more temperature sensitive than that of molybdenum
No full textThe redox potentials of strictly analogous complexes of molybdenum and tungsten were studied using temperature dependent electrochemistry in order to evaluate a proposed influence of the potentials on the use of tungsten at thermophilic conditions and the use of molybdenum at mesophilic conditions in the molybdopterin dependent oxido reductases. Each pair of molybdenum and tungsten compounds was studied under identical conditions. The studies reveal that tungsten's redox potential is always more temperature sensitive than molybdenum's with a stronger shift of the potential upon temperature change in negative or positive direction depending on the ligand system. No exceptions to this different behaviour of molybdenum and tungsten were observed. The conducted experiments are described in detail and the relevance for the use of either metal is discussed. In addition a possible reason for this fundamental difference as part of the nature of molybdenum and tungsten is proposed.Deutsche Forschungsgemeinschaft (DFG
Synthesis, characterization and structural analysis of isostructural dinuclear molybdenum and tungsten oxo-bis-mu-sulfido-benzenedithiolene complexes
No full textReactions of the molybdenum and tungsten precursors [MO(2)S(2)](2) with equimolar amounts of benzenedithiol in acetonitrile give the title compounds [M(2)O(2)(mu-S)(2)(bdt)(2)](2) with M = Mo, W and bdt = benzenedithiolate. In case a tungsten to ligand ratio of 1:2 is used the dimer forms as well but only as a minor species whereas the monomer [WO(bdt)(2)](2) is the main product. In both dimeric compounds the syn-isomers are formed referring to the position of the apical oxo ligands with respect to the M(2)S(2) plane. For the molybdenum compound this contrasts with a published crystal structure of the anti-isomer. Both complexes give highly symmetric isomorphous crystals but still show subtle differences in their bond lengths and angles around the central metal. The X-ray crystal structures of both are analyzed in detail and compared with each other and with the isomeric molybdenum compound. Differences and similarities between tungsten and both isomers of molybdenum complexes are shown to be more influenced by the conformation than by the central metal and a reason for the formation of syn- and anti-isomers based on the respective synthetic procedures is proposed. (C) 2010 Elsevier B.V. All rights reserved.DFG (Deutsche Forschungsgemeinschaft
Mono‐oxo‐bis‐dithioveratrol‐molybdate – in Solution a Model for Arsenite Oxidase and in the Solid State a Coordination Polymer with Unprecedented Binding Motifs
No full textMono-oxo-bis-dithioveratrol-molybdate was synthesized, structurally characterized, and investigated with respect to its oxo-transfer activity. The latter was compared with the activity of the analogous tungsten complex. The title complex is a structural model for molybdopterin bearing arsenite oxidase and both complexes catalyze oxo-transfer reactions successfully to 100% conversion. With the dithioveratrol ligand the oxidation of triphenylphosphine proved to be faster for the tungsten complex, which is untypical. The solid-state structure of the molybdenum complex exhibits an unexpected and very unusual polymeric structural motif consisting of the complex anion mono-oxo-bis-dithioveratrol-molybdate, sodium cations, and methanol. Infinite double-decker strands are formed with sodium bridges between the ether functions of two ligands in one strand and the Mo=O moiety of the second strand.ERC (project MocoModels
Reactions of Tin(II) Hydride Species with Unsaturated Molecules
No full textDeutsche Forschungsgemeinschaf
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
Facile Access of Stable Divalent Tin Compounds with Terminal Methyl, Amide, Fluoride, and Iodide Substituents
No full textThe stable beta-diketiminate tin(II) complexes LSnX [L = HC(CMeNAr)(2), Ar = 2,6-Pr(2)C(6)H(3)] with terminal methyl, amide, fluoride, and iodide (X = Me, N(SiMe(3))(2), F, I) are described. LSnMe (2) is synthesized by salt metathesis reaction of LSnCl (1) with MeLi and can be isolated in the form of yellow crystals in 88% yield. Compound LSnN(SiMe(3))(2) (3) was obtained by treatment of LH with 2 equiv of KN(SiMe(3))(2) in THF followed by adding 1 equiv of SnCl(2). Reaction of 2 and 3 respectively with Me(3)SnF in toluene provided the tin(II)fluoride LSnF (4) with a terminal fluorine as colorless crystals in 85% yield. 4 is highly soluble in common organic solvents, The reaction of LLi(OEt(2)) with 1 equiv of Snl(2) in diethyl ether afforded the LSnl (5). Compounds 2, 3, 4, and 5 were characterized by microanalysis, multinuclear NMR spectroscopy, and X-ray structural analysis. Single crystal X-ray structural analyses indicate that all the compounds (2, 3, 4, 5) are monomeric and the tin center resides in a trigonal-pyramidal environment.Deutsche Forschungsgemeinschaf
Facile Access of Well-Defined Stable Divalent Lead Compounds with Small Organic Substituents
No full textThe reaction of I equiv of beta-diketiminate lithium, LLi center dot OEt(2) {L = HC(CMeNAr)(2) (Ar = 2,6-iPr(2)C(6)H(3)) nacnac ligand} with I equiv of PbCl(2) in THF afforded the beta-diketiminate lead(II) chloride (1) as a yellow compound. Treatment of I with stoichiometric amounts of methyl lithium, phenyl lithium, lithium phenylacetylide, and silver triflate resulted in the divalent organolead compounds LPb(II)Me (2), LPb(11)Ph (3), LPb(II)CCPh (4), and LPb(II)OTf (5). Compounds 2 and 3 are the first stable, monomeric lead(II) derivatives involving small alkyl and aryl groups Me and Ph, respectively, supported by the beta-diketiminate ligand. Compound 4 is the first alkynyl lead(II) derivative. All compounds (2, 3, 4, 5) were characterized by microanalysis, X-ray crystallography, and (1)H, (13)C, and (207)Pb NMR spectroscopy. Single-crystal X-ray structural analyses indicate that compounds 2-4 are monomeric, and the lead center resides in a trigonal-pyramidal environment, whereas 5 has a polymeric structure. The results demonstrate the effectiveness of the beta-diketiminate ligand in creating a protected surrounding for the lead atom.Deutsche Forschungsgemeinschaf
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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