1,720,972 research outputs found
Cobalt Corroles as Electrocatalysts for Water Oxidation: Strong Effect of Substituents on Catalytic Activity
No full textTwo Co(III) complexes (1Py2 and 2Py2) of new corrole ligands H3L1 (5,15-bis(p-methylcarboxyphenyl)-10-(o-methylcarboxyphenyl)corrole) and H3L2 (5,15-bis(p-nitrophenyl)-10-(o-methylcarboxyphenyl)corrole) with two apical pyridine ligands have been synthesized and thoroughly characterized by cyclic voltammetry, UV-vis-NIR, and EPR spectroscopy, spectroelectrochemistry, single-crystal X-ray diffraction studies, and DFT methods. Complexes 1Py2 and 2Py2 possess much lower oxidation potentials than cobalt(III)-tris-pentafluorophenylcorrole (Co(tpfc)) and similar corroles containing pentafluorophenyl (C6F5) substituents, thus allowing access to high oxidation states of the former metallocorroles using mild chemical oxidants. The spectroscopic (UV-vis-NIR and EPR) and electronic properties of several oxidation states of these complexes have been determined by a combination of the mentioned methods. Complexes 1Py2 and 2Py2 undergo three oxidations within 1.3 V vs FcH+/FcH in MeCN, and we show that both complexes catalyze water oxidation in an MeCN/H2O mixture upon the third oxidation, with kobs (TOF) values of 1.86 s-1 at 1.29 V (1Py2) and 1.67 s-1 at 1.37 V (2Py2). These values are five times higher than previously reported TOF values for C6F5-substituted cobalt(III) corroles, a finding we ascribe to the additional charge in the corrole macrocycle due to the increased oxidation state. This work opens up new possibilities in the study of metallocorrole water oxidation catalysts, particularly by allowing spectroscopic probing of high-oxidation states and showing strong substituent-effects on catalytic activity of the corrole complexes.Fil: Neuman, Nicolás Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Albold, Uta. Freie Universität Berlin; AlemaniaFil: Ferretti, Eleonora. Freie Universität Berlin; AlemaniaFil: Chandra, Shubhadeep. Freie Universität Berlin; AlemaniaFil: Steinhauer, Simon. Freie Universität Berlin; AlemaniaFil: Rößner, Paul. Universitat Stuttgart; AlemaniaFil: Meyer, Franc. Universität Göttingen; AlemaniaFil: Doctorovich, Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Vaillard, Santiago Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Sarkar, Biprajit. Universitat Stuttgart; Alemani
Isolable Cu(I) Complexes of Extremely Electron-Poor, Completely Unreduced o -Quinone and “Di- o -Quinone” Ligands Stabilized through π–π Interactions in the Secondary Coordination Sphere
No full textThe copper?quinone interaction plays important roles in diverse fields such as biochemistry, catalysis, and optically/magnetically switchable materials. Despite this fact, the isolation and thorough characterization of copper(I)-quinone complexes remains a highly challenging task owing to their intrinsic instability. We herein present systems where the stability imparted by the extended π-system of a pyrene ring is used to synthesize, isolate, and crystallographically characterize the first example of a dinuclear metal complex that is bridged by a completely unreduced ?di-o-quinone?-type ligand. Additionally, we present the monocopper counterpart with the o-quinone?pyrene type of ligand. The copper complexes are redox-rich and display intriguing electrochemical, optical, and electron paramagnetic resonance (EPR) spectroscopic properties. The line-rich EPR spectra of the one-electron reduced copper(I) complexes were simulated and analyzed via density functional theory calculations. The results presented here establish π?π stacking as a viable alternative to stabilize otherwise unstable redox-active compounds with possible consequences for sensing and redox catalysis.Fil: Albold, Uta. Freie Universität Berlin.; AlemaniaFil: Hoyer, Carolin. Freie Universität Berlin.; AlemaniaFil: Neuman, Nicolás Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Sobottka, Sebastian. Freie Universität Berlin.; AlemaniaFil: Mukherjee, Arijit. Indian Institute of Technology; IndiaFil: Lahiri, Goutam Kumar. Indian Institute of Technology; IndiaFil: Sarkar, Biprajit. Freie Universität Berlin.; Alemani
Harnessing the redox-activity of quinone derived ligand systems in mono- and dinuclear 3d metal complexes for magnetic and catalytic applications
No full textHarnessing the redox-activity of quinone derived ligand systems in mono- and dinuclear 3d metal complexes for magnetic and catalytic applications
No full textA Binuclear Cobalt Complex in the Electrochemical Water Oxidation Reaction
No full textThe water splitting reaction represents an appealing approach to store solar energy. The 4e−/4H+ oxidation of water generating O2 is considered as the bottleneck in this reaction and usually requires a rather large over potential. We report on the synthesis and application of a binuclear cobalt(III) complex, 1, with two μ-OH ligands and tripodal triazole ligands, L, in the electrochemical water oxidation reaction (WOR; L=tris((1-phenyl-1H-1,2,3-triazol-4-yl)methyl)amine). The cobalt(III) centres in the complex exhibit an octahedral coordination geometry and the complex is stable in water. Electrochemical studies revealed that solutions of 1NO3 catalyse the WOR in phosphate or borate buffer. However, further analysis showed, that 1NO3 is a precursor and decomposes under the applied potential. A smooth deposit is formed on the electrode surface, which is a highly active water oxidation catalysis. The deposit consists of mainly cobalt oxide/hydroxide, which accounts for the catalytic activity, and small amounts of 1NO3
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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