1,721,024 research outputs found
Ligand Induced P-H Bond Formation vs Ligand Substitution, and a Comparison of the Reacivity of Two Isomers of [Pt2(m-PBut2)2(PBut2H)(CO)(H)]CF3SO3
No full textThe Pt-2((II)) isomeric terminal hydrides [(CO)(H)Pt(mu-PBu21)(2)Pt((PBu2H)-H-1)]CF ISO, (1a), and [(CO)Ptmu-Bu-2(1))(2)Pt((PBu2H)-H-1)(H)]CF3SO3 (1b), react rapidly with 1 atm of carbon monoxide to give the same mixture of two isomers of the P-2((I)) dicarbonyl [Pt-2(mu-PBu21)(CO)(2)((PBu2H)-H-1)(2)]CF3SO3 (3-Pt); the solid state structure of the isomer bearing the carbonyl ligands pseudo-trans to the bridging phosphide was solved by X-ray diffraction. A remarkable difference was instead found between the reactivity of la and 1b towards carbon disulfide or isoprene. In both cases 1b reacts slowly to afford [Pt-2(mu-PBu21)(mu,eta(2),eta(2)-CS2)((PBu2H)-H-1)(2)]CF3SO3 (4-Pt), and [Pt-2(mu-PBu21)(mu,eta(2),eta(2)-isoprene) ((PBu2H)-H-1)(2)]CF3SO3 (6-Pt), respectively. In the same experimental conditions, 1a is totally inert. A common mechanism, proceeding through the preassociation of the incoming ligand followed by the P-H bond formation between one of the bridging P atoms and the hydride ligand, has been suggested for these reactions
The first examples of isonitrile insertion into a phosphido bridge and the crystal and molecular structures of [Pt2(mu-P(t)Bu2){mu,eta2-P(t)Bu-2)C(=NAr)}(CNAr)2] and [Pt{mu,eta2-P(t)Bu-2)C (NHAr)}(CNAr)]2(CF3SO3)2 (Ar = p-tolyl)
No full textThe platinum(I) dinuclear carbonyl [Pt-2(mu -PBu2t)(2)((PBu2H)-H-t)(CO)] (1) reacts with organic isonitriles RNC (R = p-tolyl, Bu-t, PhCH2), yielding the mono- and disubstituted derivatives [Pt-2(mu -PBu2t)(2)((PBu2H)-H-t)(CNR)] (2, R = p-tolyl; 3, R = Bu-t; 4, R = PhCH2) and [Pt(mu -PBu2t)(CNR)](2) (5, R = p-tolyl; 6, R = Bu-t; 7, R = PhCH2). Only with the aromatic isonitrile does the reaction proceed through two further well-separated steps, giving [Pt-2(mu -PBu2t){mu,eta (2)-P(Bu-2(t))C(=NAr)}(CNAr)(2)] (8) and [Pt{mu,eta (2)-P(Bu-2(t))C(=NAr)}(CNAr)](2) (9). These arise from the unprecedented reversible isonitrile insertion into the M-P bonds of the phosphido-bridges. When 8 or 9 are reacted with CF3SO3H, the cyclic carbenes [Pt-2(mu -PBu2t){mu,eta (2)-P(Bu-2(t))C(NHAr)}(CNAr)(2)]CF3SO3 (10) and [Pt{mu,eta (2)-P(Bu-2(t))C(NHAr)}(CNAr)](2) (CF3SO3)(2) (11) are respectively formed. The crystal and molecular structures of complexes 8 and 11 were solved by X-ray diffraction
Experimental and Theoretical Investigation of the Molecular and Electronic Structure of [Zn4(μ4-S){μ-S2As(CH3)2}6] and [Cd4(μ4-S){μ-S2As(CH3)2}6]: Two Possible Molecular Models of Extended Metal Chalcogenide Semiconductors
No full textThe molecular and electronic structure of hexakis[μ-(dimethylarsinodithioate-S:S‘)]-μ4-thioxotetrazinc has been investigated by combining X-ray diffraction measurements, electrospray mass spectrometry (ESI), UV absorption spectroscopy, and density functional calculations. The polynuclear zinc complex consists of discrete “tetrazinc sulfide” moieties held together by van der Waals interactions. The unit cell contains four independent molecules and four solvent molecules. Each independent unit is characterized by a central μ4-S coordinated to four Zn ions, each of them at the center of an irregular tetrahedron of S atoms. ESI measurements point out that the synthesis of the analogous Cd derivative was successful. Crystal data are as follows: chemical formula, C12H36As6Cl1.5S13Zn4; monoclinic space group P21/n (no. 14); a = 30.4228(7) Å, b = 18.3720(5) Å, c = 32.3758(8) Å, β = 95.857(1)°; Z = 16. Theoretical calculations indicate that, despite their structural arrangement, neither the Zn nor the Cd complex can be considered molecular models of the extended ZnS and CdS. Nevertheless, the electronic transitions localized in the Zn4(μ4-S) and Cd4(μ4-S) inner cores of the title compounds have the same nature as those giving rise to the maxima in the excitation spectra of the extended Zn4S(BO2)6 and Cd4S(AlO2)6 [Blasse, G.; Dirksen, G. J.; Brenchley, M. E.; Weller, M. T. Chem. Phys. Lett. 1995, 234, 177]
CO-induced reductive elimination of P(t-Bu)2H from the platinum(II) dinuclear derivative Pt2[mu-P(t-Bu)2]2(H)2[P(t-Bu)2H]2, affording mononuclear platinum(0) or triangulo triplatinum(I,I,II) derivatives
No full textCarbon monoxide (1 atm) quantitatively converts the Pt(II) dinuclear derivative Pt-2[mu-P(t-Bu)(2)](2)(H)(2)[P(t-Bu)(2)H](2) (1) into the new (Pt2PtII)-Pt-I triangulo cluster Pt-3[mu-P(t-Bu)(2)](3)(H)(CO)(2) (2). The 44e(-) species 2 was characterized by IR and multinuclear NMR spectroscopy and by a single-crystal X-ray diffraction study. Complex 2 is formed through the slow CO-induced reductive elimination of P(t-Bu)(2)H from 1, affording the intermediate mononuclear Pt(0) carbonyl derivative Pt[P(t-Bu)(2)H](2)(CO)(2) (4), which equilibrates with the carbonyl-bridged triangulo derivative Pt-3[P(t-Bu)(2)H](3)(mu-CO)(3) (5); these are the main products under high pressures of CO. Two alternative mechanisms were examined for the subsequent formation of complex 2, the first being the rapid condensation of complex 4 with unreacted 1 while the second assumes 5 as the direct precursor of 2. Although the first mechanism cannot be conclusively rejected, the second seems the most appropriate, since under high pressures of CO/H-2 complex 2 was shown to equilibrate with 5. In the presence of an excess of other phosphines, the carbonylation of 1 yields quantitatively the mononuclear monocarbonyl derivatives Pt(PR(3))(3)(CO) (R(3) = Ph(3), Et(3), t-Bu(2)H)
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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