1,721,255 research outputs found
Synthesis and electrochemical study of some phosphine and arsine complexes of ruthenium and osmium
No full textStudies in ruthenium and osmium coordination chemistry
No full textComplexes of ruthenium and osmium with bidentate phosphine and arsine ligands have been prepared and their properties investigated. Ruthenium(III) complexes of the form trans-[Ru(L-L)2X2]+ ((L-L) = diphosphine or diarsine; X = Cl, Br) and the analogous osmium(III) and (IV) compounds, trans-[Os(L-L)2X2]+/2+ were synthesised and studied using u.v.-visible and infra-red spectroscopies. The redox properties of the complexes were studied using cyclic voltammetry and their properties compared. The stereochemistry was confirmed by x-ray crystal structures of trans-[Ru(o-C6F4(AsMe2)2Br2]BF4 and trans-[Os(o-C6H4(AsMe2)2)2Cl2]ClO4. The variation of Os-As and Os-X (X = Cl, Br) bond lengths with osmium oxidation state was investigated by the use of Os Lm-edge EXAFS 9Extended X-ray Absorption Fine Structure). Ruthenium compounds with bidentate Group 16 ligands, trans-[Ru(L-L)2X2]n+ (N = 0, (L-L) = diselenoether or ditelluroether; n = 1, (L-L) = dithioether, diselenoether; X = Cl, Br) have also been prepared and studied spectroscopically and electrochemically. 77Se and 125Te n.m.r. spectra were recorded for the ruthenium(II) compounds. The trans stereochemistry was confirmed by the x-ray crystal structure of trans-[Ru(PhSeCH2CH2SePh)2Cl2]. Ruthenium-stibine compounds of the form trans-[Ru(SbPh3)4X20+ (X = Cl, Br) have been studied and their properties investigated. The six-coordination was confirmed by an x-ray crystal structure of trans-[Ru(SbPh3)4Cl2] and this contrasts with the well-known five-coordinate phosphine compound [Ru(PPh3)3Cl2]. A functionalised o-phenylene diphosphine has been prepared and bound to a polystyrene polymer-support. Nickel, platinum, rhodium and ruthenium complexes of this supported diphosphine and model precursors have been synthesised and their properties investigated by the use of diffuse reflectance u.v.-visible and metal-edge EXAFS spectroscopies.</p
Two‐Dimensional Supramolecular Chemistry on Surfaces
No full textSupramolecular chemistry represents one of the central themes of modern chemical sciences. The use of supramolecular interactions to create complex supermolecules and self-assembled arrays on surfaces represents a new avenue of research with promise for the development of molecular-level devices
Synthesis of hydrophobic MIL-53(Al) nanoparticles in low molecular weight alcohols: systematic investigation of solvent effects
Full text linkThe effects of using low-weight alcohols, methanol and ethanol, for the synthesis of MIL-53(Al) are investigated and the results directly compared with analogous synthesis in water and N,N-dimethylformamide (DMF). When methanol is employed in the synthesis of MIL-53(Al), termed MIL 53(MeOH), several unique properties are observed. The breathing phenomenon which is known for MIL-53(Al) derivatives, prepared using water or DMF as reaction solvent, is not observed for samples prepared from methanol and the framework adopts, and remains in, the large-pore form. Thus, measurement of N2-isotherms and calculation of internal surface areas have verified that the synthesis of MIL-53(MeOH) leads to a product which is highly porous without the requirement for an energy-consuming activation process. Furthermore, X-ray diffraction measurements and scanning electron microscopy at different humidity levels reveal a reversible loss of crystallinity at high humidity levels for MIL-53(MeOH) which was not observed previously for any other known MIL-53 derivative. In contrast the synthesis of MIL-53(Al) in ethanol leads of a product with low crystallinity
Surface Self‐Assembly of Hydrogen‐Bonded Frameworks
No full textThe use of intermolecular hydrogen bonds to create two-dimensional arrays on surfaces is discussed. In particular, the supramolecular synthon strategy, is described which in principle allows the rational design and synthesis of hydrogen-bonded arrays and frameworks. The success or otherwise of using this approach is discussed, and remarkable examples of porous frameworks capable of trapping guest molecules, as well as complex and intricate design strategies that lead to tiling assemblies, are explored. Ultimately, the successful implementation of the supramolecular synthon strategy using hydrogen bonds is demonstrated, coupled with an appreciation of the complexity of energetic preferences during the self-assembly process
Characterisation and Interpretation of On‐Surface Chemical Reactions Studied by Ultra‐High‐Resolution Scanning Probe Microscopy
No full textThe investigation of supramolecular self-assembly at surfaces requires detailed characterisation at the molecular or even sub-molecular level. The primary technique that has been employed to ensure a detailed understanding of self-assembled structures is based on high-resolution scanning probe microscopy (SPM). Such techniques, notably scanning-tunnelling microscopy (STM) and atomic force microscopy (AFM) have been widely used and such techniques allow the resolution of the geometric structure of organic molecules with intramolecular resolution. The development of noncontact atomic force microscopy (ncAFM) over recent years has allowed sub-molecular imaging of the chemical, electronic, and electrostatic properties of single molecules. This chapter focuses on the use of this technique to track complex on-surface chemical reactions, investigate novel reaction products, and even synthesise new molecular structures one bond at a time
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
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