I20-Scanning-X-ray spectroscopy (XAS/XES)
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Lewis G.
Parker
,
Frances K.
Towers Tompkins
,
Jake M.
Seymour
,
Najaat
Alblewi
,
Ekaterina
Gousseva
,
Megan R.
Daw
,
Shusaku
Hayama
,
Richard P.
Matthews
,
Adam E. A.
Fouda
,
Joshua D.
Elliott
,
Christopher D.
Smith
,
Kevin R. J.
Lovelock
Diamond Proposal Number(s):
[24305, 28565, 30597, 33520, 36798]
Open Access
Abstract: Diorganozinc reagents (ZnR2, e.g. R = Et, Ph, C6F5) are widely used as Lewis acid catalysts or Lewis base reagents in their own right. However, descriptors for predicting the influence of the R substituent on ZnR2 Lewis acidity/basicity are very sparse. This is because ZnR2 liquid-phase speciation and electronic structure are unknown to date due to zinc’s ‘spectroscopically quiet’ nature and inability to measure ‘at zinc’. Here, we identify the geometric structures of ZnR2 in weakly coordinating solvents, demonstrating that electronic structure factors will dominate reactivity. We quantify the electronic structure properties that dictate ZnR2 Lewis acidity/basicity using three newly developed zinc-specific descriptors by combining the results from three zinc-specific X-ray spectroscopy methods and calculations. We provide accessible methods to pre-screen ZnR2 reactivity. Furthermore, our X-ray spectroscopy toolkit offers opportunities to develop liquid-phase descriptors that dictate reactivity for other zinc species, e.g. zinc bis-amides, battery electrolytes and enzymes.
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Oct 2025
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I09-Surface and Interface Structural Analysis
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Jake M.
Seymour
,
Ekaterina
Gousseva
,
Lewis G.
Parker
,
Frances K.
Towers Tompkins
,
Richard M.
Fogarty
,
Lennart
Frankemoelle
,
Rebecca
Rowe
,
Coby J.
Clarke
,
David A.
Duncan
,
Robert G.
Palgrave
,
Roger A.
Bennett
,
Patricia A.
Hunt
,
Kevin R. J.
Lovelock
Diamond Proposal Number(s):
[20463]
Open Access
Abstract: Liquid-phase d10s2 post-transition metal anions, such as [SnCl3]−, appear in a range of applications with a focus on catalysis and material preparation. However, little is known about their electronic structure and how it relates to reactivity. Using X-ray photoelectron spectroscopy and ab initio calculations, we demonstrate that liquid-phase d10s2 post-transition metal anions can act as dual-mode Lewis bases, interacting through the metal center and/or the ligands, with the interaction mode depending on the identity of the Lewis acid/electron acceptor. The Lewis basicity of the metal donor atom is controlled mainly by the metal identity; the ligand can be used for fine-tuning. Changing the metal center has a strong effect on the ligand basicity. These findings provide insight into d10s2 post-transition metal anion electronic structure, which will enable better molecular-level design of catalytic systems.
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Mar 2025
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
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Frances K.
Towers Tompkins
,
Lewis G.
Parker
,
Richard M.
Fogarty
,
Jake M.
Seymour
,
Ekaterina
Gousseva
,
David C.
Grinter
,
Robert G.
Palgrave
,
Christopher D.
Smith
,
Roger A.
Bennett
,
Richard P.
Matthews
,
Kevin R. J.
Lovelock
Diamond Proposal Number(s):
[29413, 30367, 31939, 33378, 35207]
Open Access
Abstract: X-ray photoelectron spectroscopy (XPS) and ab initio calculations show that fully alkylated onium cation electronic structure can be tuned using both the alkyl chains and the central onium atom. The key for tuning the central onium atom is methyl versus longer alkyl chains, allowing selection of the optimum cation for a wide range of applications, including catalysis and biocides.
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Aug 2024
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Jake M.
Seymour
,
Ekaterina
Gousseva
,
Frances
Towers Tompkins
,
Lewis G.
Parker
,
Najaat O.
Alblewi
,
Coby J.
Clarke
,
Shusaku
Hayama
,
Robert G.
Palgrave
,
Roger A.
Bennett
,
Richard P.
Matthews
,
Kevin R. J.
Lovelock
Diamond Proposal Number(s):
[24305, 28565, 30597]
Open Access
Abstract: Using a combination of liquid-phase experimental X-ray spectroscopy experiments and small-scale calculations we have gained new insights into the speciation of halozincate anions in ionic liquids (ILs). Both core and valence X-ray photoelectron spectroscopy (XPS) were performed directly on the liquid-phase ILs, supplemented by Zn 1s X-ray absorption near edge structure (XANES) spectroscopy. Density functional theory (DFT) calculations were carried out on both 1- and 2- halozincate anions, in both a generalised solvation model SMD (Solvation Model based on Density) and the gas phase, to give XP spectra and total energy differences; time-dependent DFT was used to calculate XA spectra. Speciation judgements were made using a combination of the shape and width of experimental spectra, and visual matches to calculated spectra. For 2- halozincate anions, excellent matches were found between experimental and calculated XP spectra, clearly showing that only 2- halozincate anions were present at all zinc halide mole fraction, x, studied. At specific x (0.33, 0.50, 0.60) only one halozincate anion was present; equilibria of different halozincate anions at those x were not observed. All findings show that chlorozincate anion and bromozincate anion speciation matched at the same x. Based on the results, predictions are made of the halozincate anion speciation for all x up to 0.67. Caution is advised when using differences in calculated total energies obtained from DFT to judge halozincate anion speciation, even when the SMD was employed, as predictions based on total energy differences did not always match the findings from experimental and calculated spectra. Our findings clearly establish that the combination of high-quality experimental data from multiple spectroscopies and a wide range of calculated structures are essential to have high confidence in halozincate anion speciation identification.
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Apr 2024
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Jake M.
Seymour
,
Ekaterina
Gousseva
,
Alex
Large
,
Georg
Held
,
Dennis
Hein
,
Garlef
Wartner
,
Wilson
Quevedo
,
Robert
Seidel
,
Claudia
Kolbeck
,
Coby J.
Clarke
,
Richard M.
Fogarty
,
Richard A.
Bourne
,
Roger A.
Bennett
,
Robert G.
Palgrave
,
Patricia A.
Hunt
,
Kevin R. J.
Lovelock
Diamond Proposal Number(s):
[24304, 25929]
Open Access
Abstract: Valence electronic structure is crucial for understanding and predicting reactivity. Valence non-resonant X-ray photoelectron spectroscopy (NRXPS) provides a direct method for probing the overall valence electronic structure. However, it is often difficult to separate the varying contributions to NRXPS; for example, contributions of solutes in solvents or functional groups in complex molecules. In this work we show that valence resonant X-ray photoelectron spectroscopy (RXPS) is a vital tool for obtaining atomic contributions to valence states. We combine RXPS with NRXPS and density functional theory calculations to demonstrate the validity of using RXPS to identify atomic contributions for a range of solutes (both neutral and ionic) and solvents (both molecular solvents and ionic liquids). Furthermore, the one-electron picture of RXPS holds for all of the closed shell molecules/ions studied, although the situation for an open-shell metal complex is more complicated. Factors needed to obtain a strong RXPS signal are investigated in order to predict the types of systems RXPS will work best for; a balance of element electronegativity and bonding type is found to be important. Additionally, the dependence of RXPS spectra on both varying solvation environment and varying local-covalent bonding is probed. We find that RXPS is a promising fingerprint method for identifying species in solution, due to the spectral shape having a strong dependence on local-covalency but a weak dependence on solvation environment.
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Feb 2022
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
I09-Surface and Interface Structural Analysis
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Jake
Seymour
,
Ekaterina
Gousseva
,
Alex
Large
,
Coby J.
Clarke
,
Peter
Licence
,
Richard M.
Fogarty
,
David A.
Duncan
,
Pilar
Ferrer
,
Federica
Venturini
,
Roger A.
Bennett
,
Robert G.
Palgrave
,
Kevin R. J.
Lovelock
Diamond Proposal Number(s):
[20463, 24304, 25929]
Open Access
Abstract: Ionic liquid (IL) valence electronic structure provides key descriptors for understanding and predicting IL properties. The ionisation energies of 60 ILs are measured and the most readily ionised valence state of each IL (the highest occupied molecular orbital, HOMO) is identified using a combination of X-ray photoelectron spectroscopy (XPS) and synchrotron resonant XPS. A structurally diverse range of cations and anions were studied. The cation gave rise to the HOMO for nine of the 60 ILs presented here, meaning it is energetically more favourable to remove an electron from the cation than the anion. The influence of the cation on the anion electronic structure (and vice versa) were established; the electrostatic effects are well understood and demonstrated to be consistently predictable. We used this knowledge to make predictions of both ionisation energy and HOMO identity for a further 516 ILs, providing a very valuable dataset for benchmarking electronic structure calculations and enabling the development of models linking experimental valence electronic structure descriptors to other IL properties, e.g. electrochemical stability. Furthermore, we provide design rules for the prediction of the electronic structure of ILs.
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Sep 2021
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Alexander
Large
,
Jake
Seymour
,
Wilson
Quevedo Garzon
,
Kanak
Roy
,
Federica
Venturini
,
David C.
Grinter
,
Luca
Artiglia
,
Emily
Brooke
,
Martha
Briceno De Gutierrez
,
Agnes
Raj
,
Kevin
Lovelock
,
Roger A.
Bennett
,
Tugce
Eralp-Erden
,
Georg
Held
Diamond Proposal Number(s):
[19464, 20952, 22702, 24584]
Open Access
Abstract: Near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) was used to study the chemical states of a range of alumina-supported monometallic Pd and bimetallic Pd-Pt nanocatalysts, under methane oxidation conditions. It has been suggested before that for optimal complete methane oxidation, palladium needs to be in an oxidised state. These experiments, combining NAP-XPS with a broad range of characterisation techniques, demonstrate a clear link between Pt presence, Pd oxidation, and catalyst activity under stoichiometric reaction conditions. Under oxygen-rich conditions this behaviour is less clear, as all of the palladium tends to be oxidised, but there are still benefits to the addition of Pt in place of Pd for complete oxidation of methane.
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Jan 2021
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[17787]
Abstract: The Zn 1s valence-to-core (VtC) X-ray emission spectra of six ionic liquids have been measured experimentally and simulated based upon time-dependent density-functional theory (TDDFT) calculations. The seven ionic liquids were made by mixing [C8C1Im]X and Zn(II)X2 at three different ZnX2 mole fractions (0.33, 0.50 or 0.67) for X=Cl or Br, and a further ionic liquid was made by mixing [P6,6,6,14]Cl and a mole fraction of ZnCl2 of 0.33. Calculations were performed for the [ZnX4]2-, [Zn2X6]2- and [Zn4X10]2- ions to capture the expected metal complex speciation. The VtC emission spectra showed three bands arising from single electron processes that can be assigned to emission from ligand p-type orbitals, zinc d orbitals and ligand s-type orbitals. For all seven ionic liquids, the highest occupied molecular orbital arises from the ligand p orbitals, and the spectra for the different size metal complexes for the same X were found to be very similar, in terms of both relative peak intensities and peak energies. For both experiments and TDDFT calculations, there was an energy difference of 0.5 eV between the Cl-based and Br-based metal complexes for the ligand s and p orbitals, while the Zn 3d orbital energies were relatively unaffected by the identity of the ligand. The TDDFT calculations find that for the ions with symmetrically equivalent zinc atoms ([Zn2X6]2- and [Zn4X10]2-), the most appropriate core-ionised reference state has a core-hole that is localised on a single zinc atom. In this framework, the spectra for the larger ions can be viewed as a sum of spectra for the tetrahedral complex with a single zinc atom with small variations in the structure of the coordinating ligands. Since the spectra are relatively insensitive to small changes in the geometry of the ligands, this is consistent with the small variation in the spectra measured in experiment.
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Oct 2019
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B18-Core EXAFS
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Pierrick
Clément
,
Xinzhao
Xu
,
Craig T.
Stoppiello
,
Graham A.
Rance
,
Antonio
Attanzio
,
James N.
O'Shea
,
Robert H.
Temperton
,
Andrei N.
Khlobystov
,
Kevin R. J.
Lovelock
,
Jake M.
Seymour
,
Richard M.
Fogarty
,
Alastair
Baker
,
Richard A.
Bourne
,
Brendan
Hall
,
Thomas W.
Chamberlain
,
Matteo
Palma
Diamond Proposal Number(s):
[20523, 21167]
Abstract: We present the synthesis of metal nanowires in a multiplexed device configuration using single‐walled carbon nanotubes (SWNTs) as nanoscale vector templates. The SWNT templates control the dimensionality of the wires, allowing precise control of their size, shape, and orientation; moreover, a solution‐processable approach enables their linear deposition between specific electrode pairs in electronic devices. Electrical characterization demonstrated the successful fabrication of metal nanowire electronic devices, while multiscale characterization of the different fabrication steps revealed details of the structure and charge transfer between the material encapsulated and the carbon nanotube. Overall the strategy presented allows facile, low‐cost, and direct synthesis of multiplexed metal nanowire devices for nanoelectronic applications.
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Jul 2019
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I09-Surface and Interface Structural Analysis
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Richard M.
Fogarty
,
Richard P.
Matthews
,
Matthew T.
Clough
,
Claire R.
Ashworth
,
Agnieszka
Brandt-Talbot
,
Paul J.
Corbett
,
Robert G.
Palgrave
,
Richard A.
Bourne
,
Thomas W.
Chamberlain
,
Tom
Vander Hoogerstraete
,
Paul B. J.
Thompson
,
Patricia A.
Hunt
,
Nicholas A.
Besley
,
Kevin R. J.
Lovelock
Diamond Proposal Number(s):
[10195, 12754]
Abstract: Experimental near edge X-ray absorption fine structure (NEXAFS) spectra are reported for 12 ionic liquids (ILs) encompassing a range of chemical structures for both the sulfur 1s and nitrogen 1s edges and compared with time-dependent density functional theory (TD-DFT) calculations. The energy scales for the experimental data were carefully calibrated against literature data. Gas phase calculations were performed on lone ions, ion pairs and ion pair dimers, with a wide range of ion pair conformers considered. For the first time, it is demonstrated that TD-DFT is a suitable method for simulating NEXAFS spectra of ILs, although the number of ions included in the calculations and their conformations are important considerations. For most of the ILs studied, calculations on lone ions in the gas phase were sufficient to successfully reproduce the experimental NEXAFS spectra. However, for certain ILs – for example, those containing a protic ammonium cation – calculations on ion pairs were required to obtain a good agreement with experimental spectra. Furthermore, significant conformational dependence was observed for the protic ammonium ILs, providing insight into the predominant liquid phase cation–anion interactions. Among the 12 investigated ILs, we find that four have an excited state that is delocalised across both the cation and the anion, which has implications for any process that depends on the excited state, for example, radiolysis. Considering the collective experimental and theoretical data, we recommend that ion pairs should be the minimum number of ions used for the calculation of NEXAFS spectra of ILs.
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Nov 2017
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