1,720,994 research outputs found
[V<sub>16</sub>O<sub>38</sub>(CN)]<sup>9–</sup>: a soluble mixed-valence redox-active building block with strong antiferromagnetic coupling
No full textA new discrete [V16O38(CN)]9- cluster, which displays the hitherto unknown 8- charge on the duster shell and is the first to encapsulate the cyanide anion, has been synthesized and characterized by IR and UV/vis/near-IR spectroscopy, electrochemistry, and magnetic susceptibility measurements. Bond valence sum calculations conducted on the basis of the crystal structure analysis of K9[V16O38(CN)]·13H2O confirm that this new member of the polyoxovanadate series is a mixed-valence complex. The intervalence charge transfer bands arising from intrametal interactions reveal that a localized (class II) assignment is appropriate for the duster; however, a small degree of electronic delocalization is present. Interesting possibilities exist for the incorporation of this unit into higher dimensionality framework structures, where the redox, optical, and magnetic properties can be exploited and tuned
Half a grid is better than no grid : competition between 2,2':6',2"-terpyridine and 3,6-di(pyrid-2-yl)pyridazine for copper(II)
No full textThe reaction between Cu(NO3)2·3H2O, 2,2′:6′,2′′-terpyridine (tpy) and 3,6-di(pyrid-2-yl)pyridazine (1) in a 2 : 2 : 1 molar equivalent ratio in aqueous MeCN in the presence of excess NH4PF6 leads to competition between the assembly of the dinuclear half-grid [Cu2(1)(tpy)2][PF6]4·2H2O and the mononuclear complex [Cu(1)2(OH2)][PF6]2. The yield of [Cu2(1)(tpy)2][PF6]4·2H2O has been optimized using microwave conditions. [Cu(1)2(OH2)][PF6]2 can be selectively produced by treating Cu(NO3)2·3H2O with 1 (1 : 2 molar equivalents) in aqueous MeCN in the presence of NH4PF6. The single crystal structures of [Cu2(1)(tpy)2][PF6]4·4MeNO2 and [Cu(1)2(OH2)][PF6]2 are presented. In the [Cu2(1)(tpy)2]4+ cation, ligand 1 bridges the two copper(II) centres, each of which is further coordinated by a tpy ligand. The copper(II) coordination geometry is closely associated with the arrangement of the two tpy ligands which engage in efficient face-to-face π-stacking. Magnetic data for crystalline [Cu2(1)(tpy)2][PF6]4·4MeNO2 are consistent with a weak antiferromagnetic interaction between the two copper(II) centres. EPR spectroscopic data for a powder sample of [Cu2(1)(tpy)2][PF6]4·2H2O are consistent with the dinuclear structure, but in frozen DMF and DMSO solutions, the data indicate that the dinuclear structure of [Cu2(1)(tpy)2]4+ is not preserved
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
Predicting the Position of the Hydrogen Atom in the Short Intramolecular Hydrogen Bond of the Hydrogen Maleate Anion from Geometric Correlations
No full textThe position of the hydrogen atom inside the strong and short intramolecular hydrogen bond of the hydrogen maleate anion strongly varies depending on the crystalline environment. Therefore, it has not been possible in the past to accurately determine it using X-ray diffraction data although there are 292 hydrogen maleate crystal structures with different cations in the literature. In this study, a geometric correlation for the accurate prediction of the hydrogen position in the short intramolecular hydrogen bond is presented. The results used to derive the correlation are obtained from low-temperature neutron-diffraction studies on nine different hydrogen maleate salts that span the whole range from perfectly symmetric to highly asymmetric intramolecular hydrogen bonds. Since the only variable in the correlation as derived from the neutron data is the O···O distance, the hydrogen atom position in question can subsequently be predicted using information that is accurately available from routine X-ray data. The procedure is tested using high-resolution low-temperature synchrotron X-ray diffraction structures of the same compounds, before it is applied to X-ray data sets found in the literature in which the hydrogen atom position was not determined accurately or not determined at all, e.g., using a riding model
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
All about that base: investigating the role of ligand basicity in pyridyl complexes derived from a copper-Schiff base coordination polymer
No full textThe role of ligand basicity in complex formation has been investigated using monodentate pyridines or benzimidazole (M) in combination with a solution-stable species derived form a coordination polymer, [Cu(L)] (where L = 2-(2-hydroxybenzylidene-amino)phenol). The 12 [Cu(L)(M)n] complexes generated, combined with the [Cu(L)]2(P) complexes from our previous work (where P is a polypyridyl ligand), allow us to gauge the likelihood of complex formation based on the pKa of the conjugate acid of the pyridyl ligands and Hammett parameter, σ. Above pKa ≈ 4.5, complexes are formed where the only ligands are L2− and M or P and the packing interactions are predominantly van der Waals. Below this value, complex formation is unlikely unless there additional oxygen ligands in the d_(z^2 ) of the Cu(II) ion. The structures of two literature [Cu(L)(B)] complexes, where B is a chelating bidentate pyridyl ligand are also re-examined to resolve the disorder in the [Cu(L)] moiety
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
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