1,721,003 research outputs found
SYNTHESIS AND REACTIVITY OF ETA-6-ARENE DERIVATIVES OF NIOBIUM(II), NIOBIUM(I), AND NIOBIUM(O)
No full textThe primary reduction products in the Al/AlX3/NbX5/arene system, namely Nb(eta-6-arene)(AlX4)2, X = Cl, arene = benzene, hexamethylbenzene; X = Br, arene = hexamethylbenzene, have been isolated. Tetrahydrofuran at room temperature reacts with Nb(eta-6-hexamethylbenzene)(AlBr4)2, to give the aluminium-free complex Nb2(eta-6-hexamethylbenzene)2Br4, whose crystal structure was determined by X-ray diffraction methods. In the presence of tetrahydrofuran or dimethoxyethane, the eta-6-mesitylene-tetrahaloaluminato complexes are further reduced by aluminium to bis-mesityleneniobium(0), Nb(mes)2, which undergoes: a) disproportionation with CO to [Nb(mes)2(CO)]+[Nb(CO)6]-, b) oxidation by V(CO)6 or (4,4'-dimethyl-2,2'-dipyridyl)(BPh4)2 under carbon monoxide to [Nb(mes)2(CO)]X, X = [V(CO)6]- or BPh4-. The structure of [Nb(mes)2(CO)] BPh4 has been determined by X-ray diffraction methods. In the presence of CO, Nb(mes)2 is reduced by CoCp*2 [Cp* = eta-5-C5(CH3)5] to [Nb(CO)6]-, which was isolated as its CoCp*2+ derivative; it efficiently deoxygenates CO2 to CO in the presence of carbon monoxide acceptors such as the [Nb(mes)2(THF)]+ cation
THE REDUCTION OF THE NBX5/AIX3 SYSTEM WITH ALUMINUM IN THE PRESENCE OF AROMATIC-HYDROCARBONS - AN APPROACH TO NIOBIUM(II), NIOBIUM(I), AND NIOBIUM(0) ORGANOMETALLICS
No full textThe niobium(0) compound [Nb(mes)2] (mes = 1,3,5-trimethylbenzene) was prepared not only by metal atom - ligand cocondensation, but also according to Equation (a). The chemical behavior of this compound is similar to that of the analogous complex [V(mes)2]. For example, it reacts under carbon monoxide atmosphere to give the green salt [Nb(mes)2(CO)] [Nb(CO)6]. This new, simple approach to niobium(0) compounds should facilitate their study (DME = dimethoxyethane)
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Mixed Multimetallic tris(2-pyridylmethyl)amine Based Complexes: Synthesis and Chiroptical Properties
Full text linkContinuous intensification of reaction screening methodologies has required the development of novel high-throughput analytical technologies. This urge involves also chirality related fields where nowadays novel methods for reliable, fast and effective analysis are developed. Within this field, chiroptical spectroscopies have emerged as promising techniques, in particular when they are combined with stereodynamic probes for optical signal amplification. We report here the synthesis and characterisation of a series of molecular architectures based on a modified tris(2-pyridylmethyl)amine (TPMA) complex which are able to amplify the electronic CD signal of phenylalanine. The study reports the synthesis of six novel TPMA based supramolecular architectures characterised by the presence of two different metals within the same molecule. Besides the synthesis, the study highlights how mixing metals influences the chiroptical properties of the formed compounds
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