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8th and 9th group mixed metal clusters substituted with alkynes and their reactivity towards acids
No full textAlkynes have proved to be very versatile ligands for carbonyl clusters since they
can donate from 2 to 6 electrons to up to 4 metal atoms, giving rise to various
coordination modes. The existing literature concerns mainly the tetranuclear homoand
heterometallic clusters which show structural flexibility and can contain almost
all the elements of the 6th, 7th, 8th, 9th and 10th groups of the periodic table. We
decided to study the reactivity of tetrahedral mixed metal clusters (8th-9th group)
with disubstituted mono- and di-alkynes.
[Fe2Ir2(CO)12]2- reacts with diphenylacetylene in refluxing CH3CN loosing 2 COs
and giving [Fe2Ir2(CO)10(PhCCPh)]2- whose structure consists of a metal butterfly
arrangement surmounted by the alkyne; the C-C bond is parallel to the Ir-Ir hinge.
The dropwise addition of H2SO4 to a dark red CH2Cl2 solution of this compound
leads to the neutral species [FeIr2(CO)9(PhCCPh)], that can be crystallized from
hexane at low temperature.
X-ray analysis showed that the formal loss of a Fe(CO) fragment leaves the μ3-η2
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alkyne’s coordination mode unchanged; considering the two carbon atoms as a part
of the cage, the new cluster can be described as a pseudo square pyramid.
[CoRu3(CO)11(PhCCCCPh)]- is synthesized heating a CH3CN solution of
[CoRu3(CO)13]- and 1,4-diphenylbutadiyne at 80°C for 4h; only one of the C-C
triple bonds coordinates in the dihedral angle of the metallic butterfly, parallel to
the Ru-Ru hinge. Again, the titration of a CH2Cl2 solution of the
cluster with H2SO4 promotes the limited demolition of the
molecule, but X-ray diffraction revealed also the partial
hydrogenation of the former di-alkynic chain: the persisting μ3-
coordination of the C1=C2 bond is enforced by a Ru2-C3 σ
bond, whereas the PhC4H group doesn’t bind to the metal
triangle. So the cluster’s molecular formula is [CoRu2(CO)9(PhCCCC(H)Ph)].
Cyclovoltammetric studies will ascertain if the electrochemical oxidation products
are the same obtained in this chemical way
Coordination polymers based on Rh-Ag carbide clusters
No full textCoordination polymers are nowadays intensively studied, for their potential application in nanoelectronics, and catalysis. They are typically composed by stereochemically rigid metallic ions (the linkers) and bifunctional ligands (the spacers). Organometallic linkers are very uncommon, probably because the soft transition metals in their low oxidation state do not bind stabily with the hard N- or O- donors. Howevwer, several organometallic clusters are known, which contain metal ions of the 11-12 groups. One example of this sort is [Rh6C(CO)15]2-, which has two nucleophilicic triangular faces which can be capped by [M-L] electrophilic groups (such as Ag-PPh3, Au-PPh3, Cu-NCMe). When both faces are capped, the neutral molecule [{L-M}2Rh6C(CO)15] are formed, which are stable and can be isolated in the solid state, and characterized by X-ray analysis. Moreover, it has been shown that bwo cluster unit can bind a single metal ion, as in the structurally caracterized [{Rh6C(CO)15}2Ag]-. Therefore, we tested the possibility to construct linear polymers, alternating cluster units, metal ions and, possibly, organic bifunctional spacers. As a matter of facts, the reaction between [Rh6C(CO)15]2- and [Cu(NCMe)4]PF6, or AgBF4 (in the presence of CH3CN) affords the known [{CH3CNM}2Rh6C(CO)15] (M = Cu, Ag), which were not isolated, but allowed to diffuse into a diluted solution of bifunctional heteroaromatic ligands (such as pyrazine or 4,4’ bipyridyl), obtaining cluster-containing insoluble materials. In the case of pyrazine, we also obtain single crystals suitable for X-ray analysis, and determined the solid state structure of the organometallic polymer of formula [N2C4H4-(C4H8O)Ag-Rh6C(CO)15-Ag(C4H8O)].
Suprisingly, the polymer is not linear, because the silver ions are trigonal planar, with the third coordination site occupied by a THF molecule. As an extension of this work, we aim to obtain analogous species with other metal ions, other spacers, or without solvent molecules
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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