1,721,075 research outputs found
PGSE NMR studies on RAPTA derivatives: Evidence for the formation of H-bonded dicationic species
No full textThe self-aggregation tendency of RAPTA complexes [Ru(η6-p- cymene)PTA(-R)Cl2]X, R = H (1BPh4 and IPF6) and Me (2BPh4 and 20Tf), and [Ru(η6-p-cymene)(PTA) 2Cl]X (3BPh4 and 3BF4)] in acetone-de was investigated by means of diffusion NMR spectroscopy. On increasing the concentration, the protonated species (1X) undergoes intercationic self-aggregation driven by hydrogen bonding that leads to the formation of 122+ dications and a small amount of 12X + ion triples. © 2008 American Chemical Society
Counterion-dependent deuteration of pentamethylcyclopentadiene in water-soluble cationic Rh(III) complexes assisted by PTA
Full text link[Cp*RhCl(PTA)2]X (PTA = 7-phospha-1,3,5- triazaadamantane) undergoes an H/D exchange process between the methyl groups of Cp* and D2O whose rate depends on the coordinating ability of the counterion X-. Kinetic studies and DFT calculations indicate that deuteration involves the abstraction of a Me-Cp* proton by a coordinated OH-; the formation of the latter seems to be facilitated by the presence of the N-basic centers of PTA. © 2010 The Royal Society of Chemistry
Rhenium Allenylidenes and Their Reactivity toward Phosphines: ATheoretical Study
No full textDensity functional and localMP2 calculations have been performed to study the electronic structure of
the rhenium(I) allenylidene [(triphos)(CO)2Re(dCdCdCRR0)]þ species [triphos=MeC(CH2PPh2)3;R,
R0 =aryl group] and its reactivity toward tertiary phosphines. The calculated electronic structure shows a
relatively electron-rich nature of the [(triphos)(CO)2Re]þ synthon in agreement with the experimental
behavior of the corresponding allenylidene complex [(triphos)(CO)2Re(dCdCdCPh2)]þ (R=R0=Ph).
Both the kinetics and the thermodynamics of the nucleophilic addition of tertiary phosphines PMe3-xPhx
(x=0, 1, 2, and 3) have been considered. The results indicate lower activation energies for the phosphine
attack to Cγ, which leads, however, to products higher in energy than those of the attack to CR. The
computed behavior agrees with the experimental evidence showing that the products of the attack toCγ are
kinetically favored, while the products of the attack to CR are thermodynamically favored. Finally, we
addressed the mechanism of phosphine migration fromCγ toCR, finding a low-energy path corresponding
to an incomplete detachment of the phosphine moiety that then shifts from the Cγ to the CR atoms while
remaining weakly bound to the allenylidene unit
New highly water-soluble rhodium complexes bearing 1,3,5-triaza-7-phosphaadamantane (PTA) and/or tris(hydroxymethyl) phosphine (THP)
No full textA family of cationic and neutral highly water-soluble rhodium complexes [Cp*Rh(PTA)3]Cl2 (1), [Cp*RhCl2(THP)] (2), [Cp*RhCl(THP)2]Cl (3), and [Cp*RhCl(PTA)(THP)]Cl (4) have been synthesised and fully characterised [PTA = 1,3,5-triaza-7-phosphaadamantane; THP = tris(hydroxymethyl)phosphine]. Their water-solubility increases as the number of the phosphines coordinated to the metal centre is increased. The X-ray crystal structure of compound 2 was obtained and shows the presence of intermolecular hydrogen bonding. NMR speciation studies of [Cp*RhCl2(PTA)] in deuterated water show the existence of several equilibria involving substitution processes in which the water molecules can substitute both chloride and PTA ligands. © 2009 Elsevier B.V. All rights reserved
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
Synthesis, characterization, and electrochemical behavior Of mono- and bimetallic ruthenium and rhenium allenylidenes bearing multiconjugated organic spacers
No full textNovel monoallenylidenes of Ru and Re and homobimetallic Ru/Ru and heterobimetallic Ru/Re complexes bridged by multiconjugated aromatic organic spacers such as bianthracenylidene and biphenylene were obtained and characterized by conventional spectroscopic techniques and elemental analysis. Electrochemical measurements coupled to spectroelectrochemistry and EPR spectroscopy proved that in the bis(allenylidene) complexes an electronic communication is present between either the two allenylidene bridges or the two metal centers, enticing extended intramolecular electronic mobility
Interfacial chemistry and electroactivity of black phosphorus decorated with transition metals
No full textBlack phosphorus (BP) exhibits a significant chemical reactivity toward transition metals, which is strongly dependent on its electronic and morphological features. Using as a case study metal Co atoms deposited by physical vapor deposition on chemically exfoliated BP thin films, we document that environmentally oxidized BP edges react immediately with the formation of Co(II)–POx species, but later also the basal plane strongly reacts, already at room temperature, to form an interfacial phosphide. Atomically resolved scanning tunneling microscopy data reveal the formation of a Co2P(112) layer, upon which the further growth of metal Co nanoparticles takes place. X-ray photoemission spectroscopy data show similar interfacial reactions also for atomic W, suggesting a quite general behavior. The electrochemical and photoelectrocatalytic properties of the resulting metal–BP nanohybrids are investigated by linear sweep voltammetry and electrochemical impedance spectroscopy. The Co–BP nanohybrid shows a marked stability in acid media and a significant increase of the electrocatalytic activity for the hydrogen evolution reaction with respect to bare BP, due to the formation of a very stable phosphide phase, and even an interesting photoactivity connected to the formation of p–n junction between BP and Co2P. On the other hand, the W–BP nanohybrid exhibits a modest performance in the electrocatalytic production of hydrogen because of the formation of less active oxide phases as a consequence of environmental oxidation
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