1,721,009 research outputs found
Thiophenolate clusters as potential nanosized building blocks for zinc-based nanocomposite materials: synthesis and characterisation
No full textA new type of methacrylate-substituted oxozirconium clusters: [Zr3O(OR)5(OMc)5]2 and [Zr3O(OR)3(OMc)7]2
No full textThe new clusters Zr6O2(OBu)10(OMc)10 and Zr6O2(OMe)4(OBu)2(OMc) 14 were prepared from Zr(OBu)4 and methacrylic acid. For the preparation of Zr6O2(OMe)4(OBu)2(OMc) 14, partial exchange of the butoxy groups is necessary. The clusters consist of two Zr3 subunits that dimerize via alkoxide bridges. The structures are of the same type, except that four terminal butoxy ligands in Zr6O2(OBu)10(OMc)10 are exchanged for chelating methacrylate ligands in Zr6O2(OMe)4(OBu)2(OMc) 14
Mono-, Di-, and Trimetallic Methacrylate-substituted Metal Oxide Clusters Derived from Hafnium Butoxide
No full textThe methacrylate-substituted clusters Hf4O2(OMc)12, Hf6O4(OH)4(OMc)12(BuOH), Ti4Hf4O6(OBu)4(OMc)16, and Ti2Zr5HfO6(OMc)20 (OMc=methacrylate) were prepared by reacting Hf(OBu)4, or Hf(OBu)4/Ti(OBu)4 and Hf(OBu)4/Zr(OBu)4/Ti(OBu)4 mixtures, respectively, with methacrylic acid. All clusters were characterized by X-ray structure analyses and are basically isostructural, although not in each case isomorphous, with the corresponding oxozirconium clusters. Low-temperature NMR studies revealed that the methacrylate ligands of Hf4O2(OMc)12 are highly dynamic even at −80°C
Thiophenolate clusters as potential nanosized building blocks for zinc-based nanocomposite materials: synthesis and characterization
No full textThe synthesis, the spectroscopic and structural characterization of different thiophenolate-capped zinc clusters are reported and described. In particular, different reactions of 4-chlorobenzenethiol with zinc salts yield the clusters [Me4N][Et3NH][Zn4(mu-S-C6H4-Cl)6(S-C6H4-Cl)4] (2a), [Et3NH]2[Zn4(mu-S-C6H4-Cl)6(S-C6H4-Cl)4] (2b), and [Me4N]2[Zn4(mu-S-C6H4-Cl)6(S-C6H4-Cl)4] (2c), and also the thiophenolate derivative [Et3NH]2[Zn4(mu-S-C6H5)6(S-C6H5)4] (1b) was obtained. The nanosized thiophenolate-capped clusters were investigated by 1H and 13C NMR, elemental analysis, and electrospray ionization (ESI) mass spectrometry. NMR experiments provided insights into the dynamic behaviour of the clusters. The thermal decomposition patterns of 2c were analyzed in air as well as in nitrogen, indicating the formation of zinc oxide and metallic zinc, respectively. The X-ray structure of 2a revealed that the cluster core consists of an adamantane-like framework analogous to those realized in many other M4(SR)10 metal complexes
Swelling behavior and thermal stability of poly(methylmethacrylate) crosslinked by the oxozirconium cluster Zr4O2(methacrylate)12
No full textA new isomer of the oxozirconium cluster Zr4O2(methacrylate)12 was obtained by reaction of zirconium butoxide with an excess of methacrylic acid. Contrary to the known isomer, the structure is centrosymmetric with a planar, rhombic Zr4 core. Copolymerization with a 56–207-fold excess of methylmethacrylate results in cluster-crosslinked poly(methylmethacrylate) that swells in ethyl acetate but does not dissolve. The solvent uptake during swelling decreases and the thermal stability improves with an increasing portion of the cluster. Copyright© 2001 John Wiley & Sons, Ltd
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
Formation of organically surface-modified metal oxo clusters from carboxylic acids and metal alkoxides: a mechanistic study
No full textThe reaction of Zr(OR)4 (OR = OnBu, OnPr) with methacrylic acid was monitored by extended X-ray absorption fine structure (EXAFS), 1H and 13C NMR, HPLC, and Raman measurements. The study revealed that the initial dimeric zirconium alkoxides react rapidly with the carboxylic acid and form higher aggregated multinuclear compounds. EXAFS investigations showed that the structures of the resulting aggregates in solution depend on the carboxylic acid to alkoxide ratio. In addition, the reaction rates also differ depending on this ratio; while for a methacrylic acid to zirconium alkoxide ratio of 4∶1 the reaction is slow, metal oxo clusters form rapidly with a 7∶1 ratio. Methacrylic acid ester is simultaneously formed during the reaction, with concomitant production of water, required for the formation and condensation reactions in the cluster preparation
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
Investigation of thiourea-silanes as viable precursors for the sol–gel synthesis of composites containing Zn–S complexes
No full textSulphur-functionalised trialkoxysilanes are suitable compounds for the sol–gel synthesis of silica glass embedding metal sulphide nanoclusters. In this study, three different thiourea-functionalised silanes, (EtO)3Si(CH2)3NHC(S)NHPh (SilTu), 1,4-[(EtO)3Si(CH2)3NHC(S)NH]2Ph (diSilTu) and (MeO)3Si(CH2)3N[C(S)NH(C6H5)](CH2)2NH[C(S)NH(C6H5)] (SildiTu), were used together with Zn2+ ions to investigate their potential use in the preparation of ZnS–SiO2 materials. Such precursors provide, in principle, a “molecule-to-nanocomposite” path by a direct anchoring of the metal cations to the forming silica network, via metal–sulphur (M–S) interactions. The sol–gel precursors were characterized by IR and NMR spectroscopies, and by electrospray mass spectrometry (ESI-MS). DiSilTu was also characterized by single crystal X-ray analysis. IR an
- …
