1,721,239 research outputs found
Ullmann coupling reactions on Ag(111) and Ag(110): substrate influence on the formation of covalently coupled products and intermediate metal-organic structures
No full textOn-surface reactions based on Ullmann coupling are known to proceed on coinage-metal substrates (e.g. Au, Ag,
Cu), with the chemistry of the surface strongly influencing the reaction progression. In addition, the topography of
the surface may be expected to affect the local adsorption geometry of the reactants as well as the intermediate
and final structures. Here, we investigate the effect of two different surface facets of silver, Ag(111) and Ag(110)
on the formation of organometallic and covalent structures for Ullmann-type coupling reactions. Deposition of
4,4”-diiodo-m-terphenyl molecules onto either Ag(111) or Ag(110) surfaces leads to the scission of C-I bonds
followed by the formation of organometalic zigzag structures, consisting of molecules connected by coordination
bonds to Ag adatoms. The covalently coupled product is formed by annealing each surface, leading to the removal
of Ag atoms and the formation of covalently bonded zigzag poly(m-phenylene) structures. Comparisons of the
adsorption model of molecules on each surface before and after annealing reveal that on Ag(111), structures
rearrange by rotation and elongation of bonds in order to become commensurate with the surface, whereas for the
Ag(110) surface, the similarity in adsorption geometry of the intermediate and final states means that no rotation is
required
An on-surface reaction confined within a porous molecular template
No full textOn-surface reactions based on metal-catalysed Ullmann coupling have been successfully employed to synthesise a wide variety of covalently coupled structures. Substrate chemistry and topology are both known to effect the progression of an on-surface reaction; offering routes to control efficiency and selectivity. Here, we detail ultra-high vacuum scanning probe microscopy experiments showing that templating a catalytically active surface, via a supramolecular template, influences the reaction pathway of an on-surface Ullmann-type coupling reaction by inhibiting one potential intermediate structure and stabilising another
Supramolecular Chemistry on Surfaces:2D Networks and 2D Structures
No full textSupramolecular Chemistry on Surfaces 2D Networks and 2D Structures Explore the cutting-edge in 2D chemistry on surfaces and its applications In Supramolecular Chemistry on Surfaces: 2D Networks and 2D Structures, expert chemist Neil R. Champness delivers a comprehensive overview of the rapidly developing field of two-dimensional supramolecular chemistry on surfaces. The book offers explorations of the state-of-the-art in the discipline and demonstrates the potential of the latest advances and the challenges faced by researchers in different areas. The editor includes contributions from leading researchers that address new spectroscopic methods which allow for investigations at a sub-molecular level, opening up new areas of understanding in the field. Included resources also discuss important supramolecular strategies, like hydrogen-bonding, van der Waals interactions, metal-ligand coordination, multicomponent assembly, and more. The book also provides:- A thorough introduction to two-dimensional supramolecular chemistry on surfaces - Comprehensive explorations of the characterization and interpretation of on-surface chemical reactions studied by ultra-high resolution scanning probe microscopy - Practical discussions of complexity in two-dimensional multicomponent assembly, including explorations of coordination bonds and quasicrystalline structures - In-depth examinations of covalently bonded organic structures via on-surface synthesis Perfect for polymer chemists, spectroscopists, and materials scientists, Supramolecular Chemistry on Surfaces: 2D Networks and 2D Structures will also earn a place in the libraries of physical and surface chemists, as well as surface physicists.</p
Order, disorder, and metalation of tetraphenylporphyrin (2H-TPP) on Au(111)
No full textA thermally induced order–disorder transition of tetraphenylporphyrin (2H-TPP) on Au(111) is characterised by scanning probe microscopy and X-ray photoelectron spectroscopy-based techniques. We observed that a transition from an ordered close-packed phase to a disordered diffuse phase is correlated with an on-surface cyclodehydrogenation reaction, and that additional heating of this diffuse phase gives rise to a single distinct nitrogen environment indicative of the formation of a Au–TPP species
Supramolecular Chemistry on Surfaces:2D Networks and 2D Structures
No full textSupramolecular Chemistry on Surfaces 2D Networks and 2D Structures Explore the cutting-edge in 2D chemistry on surfaces and its applications In Supramolecular Chemistry on Surfaces: 2D Networks and 2D Structures, expert chemist Neil R. Champness delivers a comprehensive overview of the rapidly developing field of two-dimensional supramolecular chemistry on surfaces. The book offers explorations of the state-of-the-art in the discipline and demonstrates the potential of the latest advances and the challenges faced by researchers in different areas. The editor includes contributions from leading researchers that address new spectroscopic methods which allow for investigations at a sub-molecular level, opening up new areas of understanding in the field. Included resources also discuss important supramolecular strategies, like hydrogen-bonding, van der Waals interactions, metal-ligand coordination, multicomponent assembly, and more. The book also provides:- A thorough introduction to two-dimensional supramolecular chemistry on surfaces - Comprehensive explorations of the characterization and interpretation of on-surface chemical reactions studied by ultra-high resolution scanning probe microscopy - Practical discussions of complexity in two-dimensional multicomponent assembly, including explorations of coordination bonds and quasicrystalline structures - In-depth examinations of covalently bonded organic structures via on-surface synthesis Perfect for polymer chemists, spectroscopists, and materials scientists, Supramolecular Chemistry on Surfaces: 2D Networks and 2D Structures will also earn a place in the libraries of physical and surface chemists, as well as surface physicists.</p
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
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