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Rhodium carbonyl clusters with interstitial nitrogen atoms. Part 1. Crystal and molecular structure of the bis(triphenylphosphine)iminium salt of the anion ennea-μ-carbonyl-hexacarbonyl-μ 6-nitrido-polyhedro-hexarhodate(1-)
No full textThe title compound, [N(PPh3)2][Rh6N(CO)15], crystallizes in the triclinic space group P1, with cell constants a = 19.841(5), b = 9.156(3), c = 16.066(5) Å, α = 95.88(3), β = 70.12(3), γ = 87.99(3)°, and Z = 2. The structure solution and refinements have been based on 6 401 significant single-crystal X-ray counter data, the final conventional R value being 0.034. The anion contains a trigonal prism of rhodium atoms with a central nitrogen atom. The Rh-Rh bond lengths belong to two classes: those within the two basal triangles (mean 2.763 Å) and the interbasal ones (mean 2.828 Å). The Rh-N interactions have a mean value of 2.130 Å. Six carbonyl ligands are bound terminally, one per rhodium atom (mean Rh-C and C-O 1.863 and 1.134 Å), and nine bridge all the polyhedral edges (mean Rh-C and C-O 2.095 and 1.153 Å). The structure is discussed in comparison with those of related carbido-carbonyl cluster species
Reaction of the unsaturated anion [Re 3H 4(CO) 10] - with mercaptans. Synthesis and X-ray Characterization of the anion [ Re 3H 3 (CO) 9(μ 3-SBu t)]
No full textThe novel anion [Re 3H 3(CO) 9(μ 3-SBu t)] -, obtained by reaction of [Re 3H 4(CO) 10] - with t-butyl mercaptan, has been characterized by IR, NMR and X-ray diffraction studies. It contains an equilateral Re 3 triangle (mean ReRe 3.091 Å), with nine terminal carbonyl groups, three for each metal atom, and a triply-bridging thiolate ligand (mean ReS 2.393 Å). The three hydrides are bridging on the edges of the triangle of metal atoms. © 1982
Synthesis and x-ray structure of the anion [Rh9(μ 3-CO)3(μ-CO)9(CO)7]3- containing a cofacial bioctahedral rhodium cluster
No full textThe novel anion [Rh9(CO)19]3-, obtained by condensation between the anions [Rh4(CO)11]2- and [Rh5(CO)15]-, contains a Rh9 metal-atom cluster formed by two condensed octahedra sharing a face
FREE-SOLUTION CAPILLARY ELECTROPHORETIC RESOLUTION OF CHIRAL AMINO-ACIDS VIA DERIVATIZATION WITH HOMOCHIRAL ISOTHIOCYANATES .1.
No full textWithin the framework of a more general study aimed at the enantiomeric
resolution of non-UV-absorbing chiral amino acids via derivatization
with chiral isothiocyanates, we have examined the applicability of two
such derivatizing agents, (S)-1-(1-naphthyl)ethyl isothiocyanate (SNEIT)
and (S)-1-phenylethyl isothiocyanate (SAMBI), to the resolution of the
enantiomers of alanine, phenylalanine, and valine in free-solution
capillary electrophoresis (FSCE). Isothiocyanates have distinct
advantages as chiral derivatizing agents in enantiospecific
chromatographic analysis, and the two reagents were readily synthesized
from commercially available reagents. SNEIT, previously not fully
described in the literature, was characterized by rigorous
physicochemical and spectroscopic means. The two diastereoisomeric
thiourea derivatives of each amino acid were separated by FSCE.
Heptakis-2,3,6-tri-O-methyl-beta-cyclodextrin was effective in assuring
the solubility of the derivatives in the working buffer and was more
efficient than beta-cyclodextrin in both dissolving the thioureas and
improving the electrophoretic resolution. Enantiomeric pairs migrated in
the order L before D. Under the conditions used SAMBI-derivatized amino
acids had longer elution times than the corresponding SNEIT derivatives.
The diastereomeric derivatives of valine and of phenylalanine had larger
separation factors alpha than the corresponding SAMBI derivatives, while
the derivatives of alanine had nearly identical alpha values with the
two derivatizing agents. The two reagents may be advantageous in the
enantiospecific analysis of amino acids, and it appears that further
exploration of these and other similar reagents is warranted
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
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