1,720,962 research outputs found
The v(CO) vibrational spectra of planar transition metal carbonyl clusters
No full textThe ν(CO) vibrational spectra of planar transition cluster carbonyls containing M(CO)4 groups are studied. It is possible to anticipate qualitatively, both for the infrared and Raman, the band intensity changes associated with increasing metallic nature of the cluster. These enable a unification of the band patterns shown by the species reported. As for (idealized) spherical clusters, the spherical harmonic model (SHM), suitably modified, becomes of more general applicability as cluster size increases, although for smaller species the tensor harmonic model (THM) makes a contribution
Tuning electronic behavior of carbonyl metal clusters by substitution of interstitial and capping atoms
No full textThe progressive replacement of Rh with Ni modulates the electronic as well as chemical properties of body-centered [Rh14_xNi(CO)9-(μ-CO)16]n- clusters (x=0, n=4; x=1, n=5 (shown here); x=2, n=4; x=5, n=2, 3) and prompts multivalence. The complexes obtained are isostructural, but not isoelectronic
Synthesis, chemical characterization, and molecular structure of Au-8{Fe(CO)(4)}(4)(dppe)(2) and Au6Cu2{Fe(CO)(4)}(4)(dppe)(2)
No full textThe new Au-8(Fe(CO)(4))(4)(P<^>P), and Au6Cu2(Fe(CO)(4))(4)(P<^>P)(2) (P<^>P= dppm, dppe) neutral cluster compounds were isolated in good yields by condensation of the [Au-3(Fr(CO)(4))(2)(P<^>D)](-) anions with Au(SEt2)Cl and CuCl, respectively, and have been characterized by IR, NMR and microanalyses. The molecular structures of Au-8( Fe(CO)(4))(4)(dppe)(2) and Au6Cu2( Fe(CO)(4))(4)(dppe)(2) have been determined by X-ray diffraction studies. Both molecules adopt a stereogeometry of the heavy atoms consisting of a triangulated and corrugated ribbon twisted around the elongation direction. Contrary to the expectations the latter displays the two copper atoms in the sites of highest connectivity. This implies that site exchange between copper and gold occurs during the synthesis
Electron-sink behaviour of the carbonylnickel clusters [Ni32C6(CO)(36)](6-) and [Ni38C6(CO)(42)](6-): Synthesis and characteriztion of the anions [Ni32C6(CO)(36)](n-) (n = 5-10) and [Ni38C6(CO)(42)](n-) (n = 5-9) and crystal structure of [PPh3Me](6)[Ni32C6(CO)(36)]center dot 4 MeCN
No full textThe hexacarbide clusters [H6-nNi38C6(CO)(42)](n-) (n = 3, 4, 5, or 6) have been directly obtained from the reaction of [Ni-6(CO)(12)](2-) with C3Cl6, whereas the related anions, [H6-nNi32C6(CO)(36)](n-) (n = 5 or 6), have been obtained by degradation under carbon monoxide of [Ni38C6(CO)(42)](6-), or upon thermal treatment at ca. 110 degrees C of [Ni10C2(CO)(42)](2-) salts. The compound [PPh3Me](6)[Ni32C6(CO)(36)] . 4 MeCN is triclinic, space group P (1) over bar (No 2), with a = 15.974(3), b = 17.474(3), c = 18.200(4) Angstrom, alpha = 61.37(2), beta = 69.31(2), gamma = 72.35(2)degrees and Z = 1; final R = 0.033. The structure of [Ni32C6(CO)(36)](6-) has an idealised O-h symmetry and is based on a truncated octahedral Ni32C6 framework, with all edges spanned by bridging carbonyl groups. The six interstitial carbide atoms are lodged in square-antiprismatic cavities, The overall geometry of the Ni32C6 core is very similar to that found previously in [HNi38C6(CO)(42)](5-), and shows very close interatomic separations. Both [Ni32C6(CO)(36)](6-) and [H6-nNi38C6(CO)(42)](n-) (n = 5 or 6) display electron-sink behaviour. Thus, they have been chemically and electrochemically reduced to their corresponding [Ni32C6(CO)(36)](n-) (n = 7-10), [Ni38C6(CO)(42)](n-) (n = 7-9) and [HNi38C6(CO)(42)](n-) (n = 6-8) derivatives, and several of the involved redox changes show features of electrochemical reversibility. In contrast, both [Ni32C6(CO)(36)](6-) and [H6-nNi38C6(CO)(42)](n-) (n = 5 or 6) support only one partially reversible oxidation step. Their different behaviour upon protonation or oxidation is an indirect, but unambiguous, proof of the hydride nature of [HNi32C6(CO)(36)](5-) and [H6-nNi38C6(CO)(42)](n-) (n = 3, 4, or 5), which could not be validated by IH-NMR spectroscopy
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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