1,720,967 research outputs found
SYNTHESIS OF MOLYBDENUM TRIOSMIUM CLUSTER COMPLEXES - REACTION OF (MU-H)2OS3(CO)10 WITH (ETA-5-C5H5)(CO)2MOCC6H4ME
No full textThe reaction of Cp(CO)2 Mo=CTol (Cp = eta-5-C5H5, Tol = p-C6H4Me) and (mu-H)2Os3(CO)10 under mild conditions (5-20-degrees-C) produces three molybdenum-triosmium mixed-metal cluster compounds, CpMoOS3(CO)11[mu-3-eta-2-C(O)CH2Tol] (4, 65%) as a major product together with two minor products CpMoOS3(CO)10(mu-3-CTol)2(mu-H) (5, 10%) and CpMoOs3(CO)10(mu-3-eta-2-C2Tol2)(mu-H) (6, 6%). Compounds 4, 5 and 6 have been isolated as crystalline solids and characterized by spectroscopic methods. Fluxionality of compound 4 has been examined by variable temperature C-13 NMR spectroscopy. Compound 5 in solution undergoes a degenerate metal framework rearrangement. H-1 NMR analysis of the tolyl methyl resonances of 5 for the rearrangement process gives DELTA-G(C)not-equal = 15.2 +/- 0.2 kcal/mol at the temperature of coalescence
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
SOLUTION DYNAMICS AND CRYSTAL-STRUCTURE OF CPMOOS3(CO)10(MU-H)2[MU-3-ETA-2-C(O)CH2TOL]
No full textThe tetranuclear heterometallic complex CpMoOs3(CO)10(mu-H)2[mu3-eta2-C(O)CH2Tol] (1, Cp=eta5-C5H5, Tol=p-C6H4Me) has been examined by variable-temperature C-13-NMR spectroscopy and by a full three-dimensional X-ray structural analysis. Complex 1 crystallizes in the orthorhombic space group Pna2(1) with a = 12.960(1) angstrom, b = 11.255(1) angstrom, c = 38.569(10) angstrom, V = 5626(2) angstrom3 and rho(calcd) = 2.71 gcm-3 for Z = 8 and molecular weight 1146.9. Diffraction data were collected on a CAD4 diffractometer, and the structure was refined to R(F) = 9.7% and R(W)F = 9.9% for 2530 data (MoKalpha radiation). There are two essentially equivalent molecules in the crystallographic asymmetric unit. The tetranuclear molecule contains a triangulated rhomboidal arrangement of metal atoms with Os(2) and Mo at the two bridgehead positions. The metal framework is planar; the dihedral angle between Os(1)-Os(2)-Mo and Os(3)-Os(2)-Mo planes is 180-degrees. A triply bridging (nu3, eta2) acyl ligand lies above the Os(1)-Os(2)-Mo plane; the oxygen atom spans the two bridgehead positions, while the carbon atom spans one bridgehead position and an acute apical position. The molecular architecture is completed by an eta5-cyclopentadienyl ligand and a semi-triply bridging carbonyl ligand on the molybdenum atom, and nine terminal carbonyl ligands-four on Os(3), three on Os(1), and two on Os(2). The two hydride ligands are inferred to occupy the Os(1)-Os(2) and Mo-Os(3) edges from structural and NMR data
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
MU-3-ETA-2-ACYL AND MU-ALKYLIDENE COMPLEXES OF A MOLYBDENUM TRIOSMIUM CLUSTER - CRYSTAL-STRUCTURE OF CPMOOS3(CO)9(MU-H)(MU-O)(MU-CHCH2TOL)
No full textInitial decarbonylation of CpMoOs3(CO)11[mu3-eta2-C(O)CH2Tol] (4; Cp = eta5-C5H5, Tol = p-C6H4Me) with Me3No/MeCN followed by reaction with dihydrogen gives the dihydride complex CpMoOs3(CO)10(mu-H)2[mu3-eta2-C(O)CH2Tol] (5) in a quantitative yield. Thermolysis of 5 induces scission of the acyl C-O to afford the three isomeric hydrido-oxo-alkylidene compounds CpMoO3(CO)9(mu-H)(mu-O)(mu-CHCH2Tol) (6a-c). Complexes 6a,b are not chromatographically separable, and compound 6c is produced either by heating a mixture of 6a and 6b in toluene (100-degrees-C) or by treating with hydrochloric acid. Compounds 4, 5, and 6a-c have been isolated as crystalline solids and have been characterized by spectroscopic (infrared, mass, H-1 and C-13 NMR) data. The molecular structure of compound 6c has been determined by a single-crystal X-ray diffraction study. Complex 6c crystallizes in the orthorhombic space group Pmn2(1) with a = 12.438 (7) angstrom, b = 8.797 (2) angstrom, c = 11.846 (4)angstrom, V = 1296 (1) angstrom3, and D(calcd) = 2.87 g cm-3 for Z = 2 and molecular weight 1118.9. Diffraction data were collected on a CAD4 diffractometer, and the structure was refined to R(F) = 6.0% and R(W)(F) = 7.5% for 1236 data (Mo Kalpha radiation). The molecule is based upon a te MoOs3 core. Each osmium atom is coordinated to three terminal CO ligands, and the molybdenum atom is bonded to an eta5C5H5, ligand. The mu-oxo, mu-alkylidene, and mu-hydrido ligands bridge each edge of one of the Os-Os-Mo triangular faces. The mu-oxo and mu-alkylidene groups are disordered out of the crystallographic mirror plane which bisects the MoOs3 core. The mu-hydride ligand is believed to span the elongated Os-Os edge of the tetrahedron. The aryl moiety (CH2Tol) is disposed toward the mu-oxo ligand, which clearly indicates that 6c is formed from a mixture of 6a and 6b by an apparent rotation of the mu-alkylidene carbon
THERMODYNAMICS OF COMPLEXATION OF LANTHANIDES BY VARIOUS DIMETHOXYBENZOATES IN AQUEOUS-SOLUTION
No full textThe stability constants of the complexes of trivalent lanthanide cations with various dimethoxybenzoates have been determined by the potentiometric titration method. The dimethoxybenzoates studied were 2,3-dimethoxybenzoate, 2,4-dimethoxybenzoate, and 2,5-dimethoxybenzoate. The thermodynamic parameters for the complexation of some lanthanide cations with 2,5-dimethoxybenzoate were measured by enthalpy titration using a titration calorimeter. All complexation measurements were made at 25 degrees C in an aqueous medium of ionic strength 0.5 M NaClO4. The thermodynamic parameters for the complexation are discussed in relation to the electronic effect of the substituent groups within the ligand. It is proposed that the enhanced stability of the dimethoxybenzoate complexes of lanthanide cations is mainly due to the polarization of the electronic charge density from the methoxy groups through the n-system of the phenyl ring to the caboxylate group. C-13 NMR evidence for charge polarization by the lanthanide cation in the complexation is presented. Theoretical calculations of the charge distributions on the carbon atoms of the 2,4-dimethoxybenzoates were also performed
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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