1,721,049 research outputs found
Catalytic hydroformylation of (1S,5S)-(???)- and (1R,5R)-(+)-??-pinene: stereoselective synthesis and spectroscopic characterization of (1S,2R,5S)-, (1S,2S,5S)-, (1R,2R,5R)- and (1R,2S,5R)-10-formylpinane
No full textCatalytic hydroformylation of (1S,5S)-(???)- and (1R,5R)-(+)-??-pinene: stereoselective synthesis and spectroscopic characterization of (1S,2R,5S)-, (1S,2S,5S)-, (1R,2R,5R)- and (1R,2S,5R)-10-formylpinan
A high-nuclearity Ni–Sb carbonyl cluster displaying unprecedented metal stereochemistries: synthesis and X-ray structure of [NEt4]6[Ni31Sb4(CO)40]·2 Me2CO
No full textThe mild oxidation of [NEt4](2)[Ni15Sb(CO)(24)] in acetone solution with SbCl3 in a ca. 3 : 1 molar ratio leads to the new high-nuclearity [Ni31Sb4(CO)(40)](6-) hexaanion, which displays two interstitial Ni and four semi-interstitial Sb atoms with unprecedented stereochemistries
The new enneanuclear nickel carbonyl anion [Ni9(CO)16]2− and its relationships with the [Ni12(CO)21]4− and [Ni6Rh3(CO)17]3− clusters
No full textThe reaction of [N(PPh3)(2)](2)[Ni-6(CO)(12)] with Cu(PPh3)(x) Cl (x = 1, 2). as well as the degradation of [N(PPh3)(2)](2)[H2Ni12(CO)(21)] with PPh3, affords the new and unstable dark orange-brown [N(PPh3)(2)](2)[Ni-9(CO)(16)]. THF salt in low yields. This salt has been characterized by a CCD X-ray diffraction determination, along with IR spectroscopy and elemental analysis. The close-packed two-layer metal core geometry of the [Ni-9(CO)(16)](2) dianion is directly related to that of the bimetallic [Ni6Rh3(CO)(17)](3-) trianion and may be envisioned to be formally derived from the hcp three-layer geometry of [Ni-12(CO)(21)](4-) by the substitution of one of the two outer [Ni-3(CO)(3)(mu - CO)(3)](2-) layers with a face-bridging carbonyl group. (C) 2002 Elsevier Science B.V. All rights reserved
New bimetallic NiRh carbonyl clusters: synthesis and X-ray structure of the trigonal antiprismatic [NiRh5(CO)14]3− and body-centered cubic [NiRh14(CO)28]4− cluster anions
No full textThe reaction of the [Ni6(CO)12]2 dianion with [Rh(COD)Cl]2 (COD /cyclooctadiene) in excess affords a complicate mixture of
bimetallic Ni /Rh clusters, from which the new [NiRh5(CO)14]3 and [NiRh14(CO)28]4 have been isolated and characterised. The
[NiRh14(CO)28]4 tetraanionic cluster has been also obtained from reacting [Ni2Rh12(CO)25]4 and [NiRh13(CO)25]5 with
[Rh(CO)2Cl]2, whereas [NiRh5(CO)14]3 has been more conveniently obtained by reduction with alkali metals or hydroxides of
[NiRh5(CO)15] . All these new bimetallic Ni /Rh carbonyl clusters have been isolated in the solid state as tetrasubstituted
ammonium salts and were characterised by elemental analysis, spectroscopy and X ray diffraction studies. The structure of the
diamagnetic [NiRh5(CO)14]3 trianion is identical to that of the homometallic [Co6(CO)14]4 tetraanion, the unique Ni atom being
disordered over the 6 equiv. trigonal antiprismatic sites. The [NiRh5(CO)14]3 trianion is slowly and irreversibly degraded to a
mixture of Ni(CO)4, [Rh(CO)4] and [Rh7(CO)16]3 upon exposure to an atmosphere of carbon monoxide. The [NiRh14(CO)28]4
tetranion displays a metal frame consisting in a hexacapped cube of rhodium atoms centered by the unique nickel atom. This metal
frame has previously been found in the homometallic [Rh15(CO)30]3 cluster. However, at difference from the latter,
[NiRh14(CO)28]4 features two less valence electrons and displays a shrinked cubic moiety. [NiRh14(CO)28]4 is slowly degraded
by carbon monoxide and halide ions to give [NiRh13(CO)25]5 and other yet uncharacterised Ni /Rh carbonyl clusters. All above
Ni /Rh clusters do not display protonation behaviour
Synthesis and characterization of new paramagnetic nickel carbonyl clusters containing antimony atoms: X-ray structure of [NEt3CH2Ph]2[Ni15(μ12-Sb)(CO)24] and [NEt4]3[Ni10Sb2(μ12-Ni)(CO)18]
No full textThe reaction of the [Ni-6(CO)(12)](2-) dianion with SbCl3 in a 2.5:1 molar ratio leads to formation of the new [Ni-15(mu(12)Sb)(CO)(24)](2-), 1(2-), cluster with good selectivity. This has been conveniently separated from [Ni-9(CO)(18)](2-), [Ni-10(SbNi(Co)(3))(2)(mu(12)-Ni)(CO)(18)](n-), 2(n-), (n = 2, 3) and other side-products by differential solubility of their [NEt4](+) salts and isolated in 50-60% yields. The corresponding [NEt3CH2Ph](2)[1] salt was obtained from [NEt4](2)[1] by metathesis in acetonitrile with [NEt3CH2Ph]Cl and has been structurally characterized. The structure of 12- consists of a distorted Sb-centered Ni-12(mu(12)-Sb) icosahedral moiety, capped by three Ni atoms on three adjacent triangular faces. The 1(2-) dianion is moderately stable to oxidation and has been electrochemically reduced to the corresponding tri-, tetra- and penta-anion; these electrogenerated species are stable only on the timescale of cyclic voltammetry. The 1(2-) dianion is readily degraded upon exposure to an atmosphere of carbon monoxide to a mixture of Ni(CO)(4) and a yet uncharacterized red-violet intermediate, which has been tentatively formulated as the [Ni6Sb(CO)(x)](2-) dianion on the basis of its spectroscopic features. The above mixture converts under nitrogen into the known 2(n-) (n = 3, 4), through the intermediate formation of the new [Ni10Sb2(mu(12)-Ni)(CO)(18)](n-), 3(n-), (n = 3, 4) species. Pure 3(3-) has been obtained by degradation of 2(3-) with two equivalents of triphenylphosphine by elimination of two equivalents of Ni(CO)(3)(PPh3) and has been structurally characterized in its tetraethylammonium salt. The Ni-centered icosahedral 3(3-) trianion shows a chemical and electrochemical redox propensity comparable to that of the parent 2(3-) compound and is readily transformed in its corresponding 3(2-) and 3(4-) anions upon oxidation and reduction, respectively. Systematic observation of apparently exceptional electron counts and redox propensity by the above Ni-centered icosahedral clusters validate the previous attribution of these properties to the presence of interstitial nickel atoms and concomitant stabilization imparted by the peripheral antimony heteroatoms. (C) 2000 Elsevier Science S.A. 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 and structural characterization of [NEt4][Fe3(μ3-O)(μ3-AuPPh3)(μ-CO)3(CO)6], the new [Au6(μ3-S)2(PPh3)6][Fe3(μ3-S)(μ-AuPPh3)(CO)9]2 and [Au6(μ3-S)2(PPh3)6][Fe5(μ3-S)2(CO)14] ionic solids containing assemblages of cluster-cations and cluster-anions
No full textThe new [Fe-3(mu(3)-O)(mu(3)-AuPPh3)(mu-CO)(3)(CO)(6)](-) and [Fe-3(mu(3)-S)(mu-AuPPh3)(CO)(9)](-) monoanionic congeners have been obtained by reacting the [Fe-3(mu(3)-E)(CO)(9)](2-) (E = O, S) dianions with one equivalent of Au(PPh3)Cl. The gold adduct of the oxygen derivative has been crystallized as tetraethylammonium and trimethylbenzylammonium salt either from THF and n-hexane or acetone and isopropyl alcohol, and structurally characterized in its tetraethylammonium salt (monoclinic, C2/c (No. 15), a = 15.859(2). b = 12.859(2), c = 40.217(8) Angstrom, beta = 96.41(1)degrees Z = 8). The [Fe-3(mu(3)-S)(mu-AuPPh3)(CO)(9)](-) gold adduct, in contrast, partially reverts to the parent dianion upon crystallization under the above experimental conditions, and could be precipitated only as the [Au-6(mu(3)-S)(2)(PPh3)(6)][Fe-3(mu(3)-S)(mu-AuPPh3)(CO)(9)](2) salt (triclinic, P (1) over bar (No. 2), a = 18.998(8), b = 19.933(8), c = 22.94(1) Angstrom, alpha = 99.91(4), beta = 98.91(4), gamma = 107.42(3)degrees Z = 2), by addition of an equivalent of the [Au-3(mu(3)-S)(PPh3)(3)](+) sulfonium cation to the reaction mixture. The [Fe-5(mu(3)-S)(2)(CO)(14)](2-) dianion does not form a gold adduct even in the presence of the sulfonium cation and only the corresponding [Au-6(mu(3)-S)(2)(PPh3)(6)][Fe-5(mu(3)-S)(2)(CO)(14)] salt could be obtained. The [Fe-3(mu(3)-O)(mu(3)-AuPPh3)(mu-CO)(3)(CO)(6)](-) and [Fe-3(mu(3)-S)(mu-AuPPh3)(CO)(9)](-) gold adducts are not isostructural and the possible factors leading to their structural diversities are discussed. The [Au-6(mu(3)-S)(2)(PPh3)(6)][Fe-3(mu(3)-S)(mu-AuPPh3)(CO)(9)](2) and [Au-6(mu(3)-S)(2)(PPh3)(6)][Fe-5(mu(3)-S)(2)(CO)(14)] salts represent further examples of ionic solids assembled from cluster-cations and cluster-anions. (C) 1999 Elsevier Science S.A. All rights reserved
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