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      X-ray Absorption Spectroscopy Systematics at the Tungsten L-Edge

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          Abstract

          A series of mononuclear six-coordinate tungsten compounds spanning formal oxidation states from 0 to +VI, largely in a ligand environment of inert chloride and/or phosphine, was interrogated by tungsten L-edge X-ray absorption spectroscopy. The L-edge spectra of this compound set, comprised of [W 0(PMe 3) 6], [W IICl 2(PMePh 2) 4], [W IIICl 2(dppe) 2][PF 6] (dppe = 1,2-bis(diphenylphosphino)ethane), [W IVCl 4(PMePh 2) 2], [W V(NPh)Cl 3(PMe 3) 2], and [W VICl 6], correlate with formal oxidation state and have usefulness as references for the interpretation of the L-edge spectra of tungsten compounds with redox-active ligands and ambiguous electronic structure descriptions. The utility of these spectra arises from the combined correlation of the estimated branching ratio of the L 3,2-edges and the L 1 rising-edge energy with metal Z eff, thereby permitting an assessment of effective metal oxidation state. An application of these reference spectra is illustrated by their use as backdrop for the L-edge X-ray absorption spectra of [W IV(mdt) 2(CO) 2] and [W IV(mdt) 2(CN) 2] 2– (mdt 2– = 1,2-dimethylethene-1,2-dithiolate), which shows that both compounds are effectively W IV species even though the mdt ligands exist at different redox levels in the two compounds. Use of metal L-edge XAS to assess a compound of uncertain formulation requires: (1) Placement of that data within the context of spectra offered by unambiguous calibrant compounds, preferably with the same coordination number and similar metal ligand distances. Such spectra assist in defining upper and/or lower limits for metal Z eff in the species of interest. (2) Evaluation of that data in conjunction with information from other physical methods, especially ligand K-edge XAS. (3) Increased care in interpretation if strong π-acceptor ligands, particularly CO, or π-donor ligands are present. The electron-withdrawing/donating nature of these ligand types, combined with relatively short metal–ligand distances, exaggerate the difference between formal oxidation state and metal Z eff or, as in the case of [W IV(mdt) 2(CO) 2], exert the subtle effect of modulating the redox level of other ligands in the coordination sphere.

          Abstract

          A series of six-coordinate tungsten compounds, primarily with phosphine and/or Cl ligands and spanning formal oxidation states 0 → +VI, were examined by L-edge X-ray absorption spectroscopy. The estimated branching ratio derived from the L 3- and L 2-edge intensities and the L 1 rising-edge energies correlate with formal oxidation state. The data reported were applied to compounds with ambiguous electronic structure descriptions due to the presence of π-accepting and redox-active ligands.

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          Generalized Gradient Approximation Made Simple

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            The derivative discontinuity in the strong-interaction limit of density functional theory

            We generalize the exact strong-interaction limit of the exchange-correlation energy of Kohn-Sham density functional theory to open systems with fluctuating particle numbers. When used in the self-consistent Kohn-Sham procedure on strongly-interacting systems, this functional yields exact features crucial for important applications such as electronic transport. In particular, the step-like structure of the highest-occupied Kohn-Sham eigenvalue is very well captured, with accurate quantitative agreement with exact many-body chemical potentials. Whilst it can be shown that a sharp derivative discontinuity is only present in the infinitely strong-correlated limit, at finite correlation regimes we observe a slightly-smoothened discontinuity, with qualitative and quantitative features that improve with increasing correlation. From the fundamental point of view, our results obtain the derivative discontinuity without making the assumptions used in its standard derivation, offering independent support for its existence.
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              The Local Compressibility of Liquids near Non-Adsorbing Substrates: A Useful Measure of Solvophobicity and Hydrophobicity?

              We investigate the suitability of the local compressibility chi(z) as a measure of the solvophobicity or hydrophobicity of a substrate. Defining the local compressibility as the derivative of the local one-body density w.r.t. the chemical potential at fixed temperature, we use density functional theory (DFT) to calculate chi(z) for a model fluid, close to bulk liquid-gas coexistence, at various planar substrates. These range from a `neutral' substrate with a contact angle of approximately 90 degrees, which favours neither the liquid nor the gas phase, to a very solvophobic, purely repulsive substrate which exhibits complete drying (i.e. contact angle 180 degrees). We find that the maximum in the local compressibility, which occurs within one-two molecular diameters of the substrate, and the integrated quantity chi_ex (the surface excess compressibility, defined below) both increase rapidly as the contact angle increases and the substrate becomes more solvophobic. The local compressibility provides a more pronounced indicator of solvophobicity than the density depletion in the vicinity of the surface which increases only weakly with increasing contact angle. When the fluid is confined in a parallel slit with two identical solvophobic walls, or with competing solvophobic and solvophilic walls, chi(z) close to the solvophobic wall is altered little from that at the single substrate. We connect our results with simulation studies of water near to hydrophobic surfaces exploring the relationship between chi(z) and fluctuations in the local density and between chi_ex and the mean-square fluctuation in the number of adsorbed molecules.
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                Author and article information

                Journal
                Inorg Chem
                Inorg Chem
                ic
                inocaj
                Inorganic Chemistry
                American Chemical Society
                0020-1669
                1520-510X
                28 July 2015
                28 July 2014
                18 August 2014
                : 53
                : 16
                : 8230-8241
                Affiliations
                []Department of Chemistry, Tulane University , 6400 Freret Street, New Orleans, Louisiana 70118, United States
                []Department of Chemistry and Biochemistry, Lamar University , Beaumont, Texas 77710, United States
                [§ ]Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University , Ithaca, New York 14853, United States
                []Max-Planck-Institut für Chemische Energiekonversion , Stiftstrasse 34-36, D-45470, Mülheim an der Ruhr, Germany
                []WestCHEM, School of Chemistry, University of Glasgow , Glasgow G12 8QQ, United Kingdom
                Author notes
                [* ]E-mail: donahue@ 123456tulane.edu . (J.P.D.)
                Article
                10.1021/ic500256a
                4139175
                25068843
                09557b14-44a5-4e51-a48b-336014b26371
                Copyright © 2014 American Chemical Society

                Terms of Use

                History
                : 31 January 2014
                Funding
                National Institutes of Health, United States
                Categories
                Article
                Custom metadata
                ic500256a
                ic-2014-00256a

                Inorganic & Bioinorganic chemistry
                Inorganic & Bioinorganic chemistry

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