1,721,148 research outputs found
Supplementary Dataset for Thesis: Coordination Chemistry of High Valent Early Transition Metals with Neutral Donor Ligands: Towards Precursors for the Electrodeposition and LPCVD of Molybdenum and Tungsten Dichalcogenides
No full textThis dataset contains crystal cif. files and ESI documents to support the thesis entitled: Coordination Chemistry of High Valent Early Transition Metals with Neutral Donor Ligands: Towards Precursors for the Electrodeposition and LPCVD of Molybdenum and Tungsten Dichalcogenides, available at https://eprints.soton.ac.uk/446982/</span
Coordination Chemistry of high valent early transition metals with neutral donor ligands: towards precursors for the electrodeposition and LPCVD of molybdenum and tungsten dichalcogenides
No full textThe work in this thesis concerns the development of several new series of high valent Group VI (Mo, W) complexes and explores their application for the deposition of molybdenum and tungsten dichalcogenide thin films via electrodeposition and low-pressure chemical vapour deposition. A review of the relevant background literature is presented in Chapter 1, while Chapter 2 presents an investigation to explore the chemistry of tungsten(VI) and develop the first systematic series of tungsten oxytetrachloride and thiotetrachloride coordination complexes, six-coordinate [WECl4(L)] or [(WECl4)2(µ-L-L)] (E = O or S) or seven-coordinate [WECl4(L-L)] and to explore their properties. The ligands used include phosphine oxides (dppeO2, dppmO2, OPPh3 and OPMe3) and N-heterocycles (2,2’-bipy, 1,10-phen and py). Unusual seven-coordinate pentagonal bipyramidal tungsten(VI) oxo- and thio-tetrachloride complexes with a series of phosphine and arsine ligands to give complexes of the form [WECl4(LL)] (E = O or S), are reported in Chapter 3, together with investigation of monodentate ligands. The ligands used include o-C6H4(E’Me2)2 (E’ = P or As), Me2P(CH2)2PMe2, PMe3, AsEt3 and oC6H4(PPh2)2. The coordination chemistry of a series of WSCl4 complexes with thioethers and comparative WOCl4 complexes are described in Chapter 4. Softer selenium donor ligands are also investigated and the properties of hard metal-soft ligand interactions explored. Potential precursors for low pressure chemical vapour deposition are identified on the basis of certain criteria i.e. butyl substituent ligands and M:E ratio. Reported in Chapter 5, [(WSCl4)2( i PrS(CH2)2Si Pr)], [WSCl3( i PrS(CH2)2Si Pr)] and [WSCl4(Sn Bu2)] were tested as single source LPCVD precursors. [(WSCl4)2( i PrS(CH2)2Si Pr)] and [WSCl4(Sn Bu2)] deposit 4H-WS2 thin films, the two W(VI) precursors deposited continuous films with a W:S ratio of 1:2.2 consistent with WS2. These are the first examples of single source LPCVD precursors to deposit WS2 thin films and the films have been characterised by Raman spectroscopy, grazing incidence XRD and in-plane XRD, EDX, WDX, XPS and SEM. Presented in Chapter 6, a family of MoOCl3 complexes with a range of neutral donor ligands, with a particular emphasis on thio-, seleno- and telluro-ether ligands, allowing comparisons to be drawn to the coordination complexes of WECl4 (E = O or S). The reaction of MoOCl4 with various ligands is investigated and compared to the MoOCl3 coordination complexes. The development and synthesis of a series of potential precursors suitable for the electrodeposition of ME2 (M = Mo or W; E = S or Se) thin films using non-aqueous solvents is discussed in Chapter 7, particularly including the synthesis of precursors for the electrodeposition of MoS2 and WS2 and their respective electrochemical studies. Deposited films have been characterised by Raman spectroscopy, grazing incidence XRD, EDX, WDX and SEM analysis. Where possible, new complexes have been characterised by IR, Raman, multinuclear NMR ( 1 H, 31P{1 H}, 77Se{1 H} and 95Mo where appropriate), UV-V is spectroscopy, magnetic measurements, elemental analysis and single crystal X-ray structures
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
Pentagonal bipyramidal complexes of WOCl<sub>4</sub> and WSCl<sub>4</sub> with diphosphine and diarsine ligands
No full textThe seven-coordinate tungsten(VI) complexes, [WOCl4{o-C6H4(EMe2)2}] and [WSCl4{o-C6H4(EMe2)2}] (E = P, As), have been prepared by reaction of WOCl4 or WSCl4 with the ligands in anhydrous CH2Cl2 or toluene, and fully characterised by microanalysis, IR, 1H and 31P{1H} NMR spectroscopy. The X-ray crystal structures of [WOCl4{o-C6H4(AsMe2)2}] and [WSCl4{o-C6H4(PMe2)2}] have been determined and revealed pentagonal bipyramidal geometries with axial O/Cl or S/Cl. Attempts to isolate similar complexes with o-C6H4(PPh2)2, PMe3 or AsEt3 were unsuccessful, due to facile reduction of the tungsten centre. Several reduction products have also been identified crystallographically, including the tungsten(V) species, [WOCl3{o-C6H4(PMe2)2}], WOCl3{o-C6H4(PMe2)(P(O)Me2)}] and [WCl4{o-C6H4(PPh2)2}2][WCl6]
Synthesis, properties and structural features of molybdenum(V) oxide trichloride complexes with neutral chalcogenoether ligands
No full textComplexes of oxotrichloromolybdenum(V) with neutral group 16 donor ligands, [MoOCl3(L–L)] (L–L = RS(CH2)2SR, R = iPr, Ph; MeS(CH2)3SMe; MeSe(CH2)2SeMe; MeSe(CH2)3SeMe), [{MoOCl2(EMe2)}2(μ-Cl)2] (E = S, Se, Te), [(MoOCl3)2{o-C6H4(EMe)2}]n (E = Se or Te) and [(MoOCl3)2{MeTe(CH2)3TeMe}]n, have been obtained by reaction of the ligands with [MoOCl3(thf)2] or MoOCl3 in either CH2Cl2 or toluene, and characterised by microanalysis, IR and UV-visible spectroscopy and magnetic measurements. The telluroethers are the first examples containing Mo in a positive oxidation state. X-ray crystal structures are reported for the six-coordinate fac-[MoOCl3{MeS(CH2)3SMe}], mer-[MoOCl3{iPrS(CH2)2SiPr}] and mer-[MoOCl3{MeSe(CH2)2SeMe}], as well as the six-coordinate chloride-bridged dimers, [{MoOCl2(SMe2)}2(μ-Cl)2] and [{MoOCl2(SeMe2)}2(μ-Cl)2]. The structure of the mixed-valence decomposition product, [MoIVCl{o-C6H4(TeMe)2}2(μ-O)MoVOCl4], was also determined. In toluene solution MoOCl4 is reduced by MeS(CH2)3SMe to produce the Mo(V) complex, [MoOCl3{ MeS(CH2)3SMe}]. Crystal structures of the previously unknown diphosphine analogue, [MoOCl3{Me2P(CH2)2PMe2}], and the mixed-valence derivative [MoIVCl{Me2P(CH2)2PMe2}2(μ-O)MoVOCl4] are also reported for comparison and help to clarify earlier contradictory literature reports. In contrast to the dimeric EMe2 complexes, [{MoOCl2(EMe2)}2(μ-Cl)2], PMe3 forms the monomeric complex, fac-[MoOCl3(PMe3)2]
Coordination complexes and applications of transition metal sulfide and selenide halides
No full textMetal chalcogenide halides are less studied analogues of metal oxide halides, where the oxido-group is replaced by heavier Group 16 elements, specifically sulfur, selenium or tellurium. This article reviews the chemistry of neutral ligand complexes of molecular chalcogenide halides of the d-block metals. The majority of these complexes contain the higher oxidation states of niobium, tantalum and tungsten, with more limited examples of titanium, molybdenum and vanadium compounds. The synthesis, structures and properties are described, and areas in need of further study identified. The recent application of several examples as low pressure chemical vapour deposition reagents for the production of thin films of semiconducting metal dichalcogenide materials is also discussed.</p
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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