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A homoleptic zirconium complex with four bulky eta(2)-pyrazolato ligands
No full textTwo new tetrakis(eta(2)-pyrazolato) zirconium complexes are prepared from the reaction of Zr(CH2Ph)(4) with bulky pyrazolate ligands bearing indenylmethyl (HL1) or fluorenylmethyl (HL2) substituents, respectively. Zr(L-2)(4) has been analyzed by X-ray crystallography, which represents the first structural characterisation of a homoleptic eta(2)-pyrazolato zirconium compound
Bifunctional Cp boolean AND N complexes - Unusual structural features and electronic coupling in highly preorganized bimetallic systems
No full textA homoleptic zirconium complex with four bulky eta(2)-pyrazolato ligands
No full textTwo new tetrakis(eta(2)-pyrazolato) zirconium complexes are prepared from the reaction of Zr(CH2Ph)(4) with bulky pyrazolate ligands bearing indenylmethyl (HL1) or fluorenylmethyl (HL2) substituents, respectively. Zr(L-2)(4) has been analyzed by X-ray crystallography, which represents the first structural characterisation of a homoleptic eta(2)-pyrazolato zirconium compound
Combining organometallic and Werner-type coordination sites in highly preorganized heterobimetallic systems
No full textA first example of a novel class of preorganized bimetallic complexes is reported, in which both an organometallic CpMn(CO)2 fragment and a classical Werner-type coordination site are arranged in close proximity by means of a bridging pyrazolate. The synthetic route starts from N-protected bis(chloromethyl)pyrazole and involves sequential attachment of the manganese part and the chelating N-donor compartment, bis(pyridylmethyl)amine, at the different sides of the ligand backbone. Pyrazole binding to the manganese(I) is achieved by photoinduced substitution of CO, and the adjacent N4-coordination pocket is suited to accommodate a second metal ion. The heterodinuclear MnZn complex 4 is characterized crystallographically and its redox chemistry investigated by spectroelectrochemical methods.publishe
Scaffolds: Effects of Bulky Substituents and Coligands on Structures and M···H−C Interactions
No full textA series of nickel(II) and palladium(II) complexes [L2M2](2+) have been prepared and structurally characterized, where L is a pyrazolate ligand with bulky 2,6-dimethyl- or 2,6-di(isopropyl)anilinomethyl side arms. Coordinating counter anions such as chloride can bind to axial sites of the dinickel species in a solvent-dependent process, giving rise to five-coordinate high-spin metal ions. In the case of weakly coordinating anions, the metal ions are found in roughly square-planar environments, and the structures are governed by the tendency of the bulky aryl groups to avoid each other, which forces the methyl or isopropyl substituents in the aryl 2- and 6-positions to approach the metal ions from the axial directions. This leads to drastic low-field shifts of the respective H-1 NMR signals, e.g. delta = 7.86 ppm for the isopropyl -CH which comes in close proximity to the low-spin nickel(II) center. The relevance of such low-field NMR resonances of protons close to the axial sites of d(8) metal ions for possible three-center four-electron (MH)-H-...-C hydrogen bonds involving the filled d(z)(2) orbital of the metal ion is discussed. In the present case, attractive (MH)-H-... interactions are assumed to be of no major significance. This was corroborated by the structure of a further [L2Ni2](2+) type complex where the anilinomethyl side arms bear only a single 2-isopropyl group, which was found rotated away from the metal. Additional spectroscopic and electrochemical properties of the various complexes are reported. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
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
Electronic Coupling in a Highly Preorganized Bimetallic Complex Comprising Pyrazolate-Bridged CpMn(CO)2 Moieties
No full textBy means of a multistep synthetic procedure a dimanganese complex has been prepared, in which a N,N′-bridging pyrazolate ligand spans two CpMn(CO)2 subunits in a highly preorganized chelate arrangement. The Xray crystallographic analyses of the MnIMnI complex K+1− and of its non-chelate precursor complex elucidate details of the molecular structure, in particular an unusual pyrazolate binding mode in the solid state and intertwining of the CO ligands in the crowded bimetallic array 1−. The MnIMnI compound (1−), the mixed-valent MnIMnII (1), and the oxidized MnIIMnII form (1+) have been characterized by various analytical and spectrosopic methods, such as electrochemistry, variable-temperature EPR spectroscopy, IR spectroelectrochemistry, and UV/Vis/NIR spectroelectrochemistry as well as by DFT and TD-DFT calculations. Strong electronic coupling in the mixed-valent complex is observed, but time- (and temperature-) dependent valence detrapping occurs, thus placing 1 in class II according to the Robin and Day assignment, close to the class II/III transition. From variable-temperature EPR spectroscopy a rough estimate of the activation energy and rate for thermal electron transfer can be deduced, with Eth≠=13.6 kJ mol−1 and kth=2.6×1010 s−1 at 298 K. Unexpectedly, no intervalence CT transition for 1 is detected in solution, but one appears in the optical spectrum of solid 1. The conclusions drawn from experiments are fully supported by DFT calculations that were carried out for all three forms of the dimanganese complex. A broken symmetry treatment for mixed-valent 1 reveals almost perfect localization of both spin and charge on one Mn center. According to TD-DFT the first excited states of 1 give rise to the IT processes in the NIR-energy region, as observed in the solid-state spectrum. The HOMOs are located at the Mn ions and are favorably arranged for π interactions with the bridging pyrazolate.publishe
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