1,721,030 research outputs found
Deuterium quadrupolar coupling constants of deuteride bridging ligands : A study on rhenium hydrido carbonyl clusters
No full textDeuterium variable-temperature T, measurements have been performed for a series of rhenium carbonyl clusters containing doubly and triply bridging deuterides, namely Re-2(mu-D)(2)(CO)(8) (1), Re-3(mu-D)(3)(CO)(12) (2), Re-4(mu(3)-D)(4)(CO)(12) (3), [NEt4] [Re-3(mu-D)(4)(CO)(10)] (4), [NEt4] [Re3-(mu-D)(3)(mu-Cl)(CO)(10)] (5), and [NEt4] [Re-3(mu-D)(4)(CO)(9)] (6). The deuterium quadrupolar coupling constants (DQCC) of the deuteride ligands have been evaluated for compounds 1-5, while the fluxionality of 6 hampered such a determination. The experimental DQCC of compound 3 (21.8 kHz) was, until now, the smallest found for organometallic compounds. Overall the DQCC values span a 4-fold range, and their fine-tuning depends on the bridging mode of the deuteride ligands (mu 3 vs mu), the local unsaturation degree of the Re atoms bridged by the deuteride, and the presence of other bridging ligands. The experimental DQCC's of rhenium derivatives and those of bridging deuterides in Cr, W, and Os clusters linearly correlate with the respective metal-hydrogen stretching frequencies
Solid State and Solution 13C and 31P nmr Spectroscopy for Structural Characterization of Ni(PCy3)2(CO2)
No full text13C and 31P nmr Spectroscopy for Structural Characterization of Carbon Dioxide Metal Complexes: the Case of Ni(PCy3)2(CO2)
No full textEthoxylation of fatty alcohols promoted by an aluminum alkoxide sulphate catalyst
No full textAluminum alkoxides are moderately active in promoting the ethoxylation of fatty alcohols. When these alkoxides are treated with pure sulfuric acid (100% by weight) in a stoichiometric ratio, the catalytic activity is strongly increased initially but it decreases rapidly giving place to products being very interesting for industry as they contain not more than two or three ethylene oxide adducts. These products are useful as raw materials for producing surfactants by sulphonation. Aluminum in the catalyst used shows all the possible coordination numbers, as demonstrated with the aid of 27Al NMR. The catalyst shows a very feeble Bronsted activity. As a consequence, small amounts of polyglycols are formed during reaction, in respect to the large amounts of ethoxylated dodecanol. Reaction rates are strongly inhibited by the presence of a Lewis base such as, for example, triphenylphosphine. The reaction seems to occur in the coordination sphere of the aluminum atoms. Other factors influencing activity and selectivity have been examined and a kinetic model has been developed on the basis of a reasonable reaction mechanism
NMR-STUDY OF THE CHEMICAL-EXCHANGE OF THE HYDRIDO LIGANDS IN THE BIS(BIS(DIPHENYLPHOSPHINO)ETHANE)TRIHYDRIDODIPLATINUM(II) CATION BY T1, T2, AND HD ISOTOPIC PERTURBATION
No full textProton longitudinal and transverse relaxation rates of hydrido resonances of different isotopomers in [H3Pt2(Dpe)2][BF4] [Dpe = bis(diphenylphosphino)ethane] show significant differences in the satellite peaks with respect to the central ones that can be used to evaluate the activation energy of the intramolecular exchange process and the chemical shift separation between bridging and terminal sites. An alternative route to get an estimation of the chemical shift values of the bridging and terminal hydrides in this derivative has been pursued by considering the isotopic shift of the three H-3, H2D, and HD2 isotopomers at different temperatures
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
Synthesis and VT-NMR study of cationic hydride platinum clusters
No full textThe synthesis of three trinuclear platinum hydrides [Pt3(L-L)3(H)3]+ (L-L = 1,2-bis(diphenylphosphino)ethane, dppe, l; 1-diphenylphosphino-2-diphenylarsinoethane, dppae. 2; 1,2-bis(diphenylarsino)ethane, dpae, 3) is reported. The complexes were characterized by IR, FAB-MS, and NMR (1H,31P and195Pt) spectroscopic techniques. The fast exchange of the hydride ligands, observed at ambient temperature, is frozen out at low temperature. The low-temperature1H and31P NMR spectra are consistent with an open array of Pt atoms in the clusters, in keeping with a 16-electron configuration on each platinum atom. Two of the hydride ligands are terminally bonded to two metal centers, whereas the third one is μ3-coordinated, interacting more tightly with the unique platinum atom
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
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