I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[35994]
Abstract: Gold catalysis provides access to a remarkable array of complex carbon scaffolds, but the use of silver salts to activate gold(I) chloride precatalysts can be problematic due to Ag(I) light sensitivity, hygroscopicity, redox activity, and interference with the desired catalysis. Although H-bond donors are a promising alternative to silver salts, they still suffer from much lower activity and narrower applicability, as Au–Cl cleavage remains rate limiting. To address these limitations, we have rationally designed a self-activating phosphine Au(I) chloride complex that incorporates a supramolecular chloride receptor in the form of an anthracene bisurea quintuple H-bond donor. In the absence of any additive, this complex promotes multiple intra- and intermolecular reactions, with a catalytic activity rivalling traditional inorganic chloride scavengers. Mechanistic studies for the model reaction show that the exceptional chloride binding ability of the anthracene bisurea unlocks access to a zwitterionic catalyst resting state where the Au─Cl bond has been cleaved, thus significantly reducing barriers for catalysis. The principles uncovered in this work show how supramolecular anion recognition moieties impact catalyst speciation and enhance performance, enabling for the first time H-bond donors to compete with inorganic chloride scavengers in terms of activity and generality.
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Jan 2026
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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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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[40688]
Open Access
Abstract: The β-diketiminato calcium hydride, [(BDI)CaH]2 (BDI = HC{(Me)CNDipp}2, where Dipp = 2,6-i-Pr2C6H3), reacts with [Zn{N(SiMe3)2}2] and [Zn(TMP)2] (TMP = 2,2,6,6-tetramethylpiperidide) to provide labile species and complex equilibria with a degree of commonality in ultimately providing the products of calcium to zinc β-diketiminate transmetalation. The silazide system provides the known [(BDI)Ca{N(SiMe3)2}] and the heterobimetallic, [(BDI)Ca{N(SiMe3)2}(μ-H)Zn]2, as a viable instrument for ligand transfer to yield [(BDI)ZnH] as the final reaction product. In contrast, the TMP-derived system evidences an enhancement in Brønsted basicity, yielding [(BDI)Zn(C6H5)] by deprotonation of the benzene solvent. This process occurs via the heterobimetallic [(BDI)Ca(μ-N{C(CH3)2CH2}2CH)(μ-H)Zn(μ-H)]2 and the previously unreported calcium amide [(BDI)Ca(TMP)]. The [(BDI)Zn(C6H5)] produced by this reaction may be exploited in biphenyl synthesis by a telescoped palladium-catalyzed cross-coupling with bromobenzene, which is unaffected by the presence of the other residual reaction products. This protocol has also been extended to the deprotonation of several further nonactivated arenes to yield the corresponding β-diketiminato arylzinc reagents with only mesitylene providing 3,5-dimethylbenzyl formation by C(sp3)-H deprotonation. Although [(BDI)Ca(TMP)] reacts with both benzene and toluene, with the latter reaction providing the calcium benzyl, [(BDI)Ca(CH2C6H5)], and it is plausible that the latter species arises from initial C(sp2)-H deprotonation and subsequent isomerization, density functional theory (DFT) calculations identify arene deprotonation to be kinetically and thermodynamically disfavored. The bimetallic derivative, [(BDI)Ca(μ-N{C(CH3)2CH2}2CH)(μ-H)Zn(μ-H)]2, cannot be definitively identified as the agent of arene deprotonation. We conclude, however, that the zinc arylation process requires the synergic cooperation of both metals.
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Aug 2025
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B18-Core EXAFS
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Tanja E.
Parmentier
,
Anna
Lazaridou
,
Joseph
Cartwright
,
Ben
Davies
,
Simon
Dawson
,
Grazia
Malta
,
Simon
Freakley
,
Thomas E.
Davies
,
David J.
Morgan
,
Simon
Kondrat
,
Christopher J.
Kiely
,
Samuel
Pattisson
,
Nicholas F.
Dummer
,
Graham J.
Hutchings
Diamond Proposal Number(s):
[15151]
Open Access
Abstract: The formation of C–C bonds through coupling reactions is an important industrial process. The ability of Au to catalyze such reactions has been reported, with both homogeneous and heterogeneous catalyst examples. Previous work has shown that carbon-supported cationic and nanoparticulate Au are active for the homocoupling of phenylboronic acid to biphenyl. However, the stability of supported cationic Au is short-lived, and the formed nanoparticles were suggested to be the active species. Through the synthesis of two types of supported cationic Au catalysts, utilizing either aqua regia or acetone solvents, we show that both catalysts develop nanoparticulate Au species early in the reaction; however, only the aqua regia prepared catalyst is active. We ascribe the activity of the aqua regia prepared Au catalyst to excess Cl and the presence of C–Cl surface species in combination with Au. Carbon treated with aqua regia was inactive; however, when used as a support for Au deposited with acetone or via a sol immobilization method, activity was comparable to the aqua regia prepared catalyst. The role of C–Cl and Au nanoparticles is discussed with respect to their correlation to the biphenyl yield, which is shown to be significant only when the C–Cl species are present on the catalyst.
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Jun 2025
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I18-Microfocus Spectroscopy
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Gabriel
Karras
,
Stuart
Bartlett
,
Edward
Bowman
,
Sam
Liewis
,
Ben
Coulson
,
Ann
Fitzpatrick
,
Lauren
Hatcher
,
Konstantin
Ignatyev
,
Mark
Warren
,
Michael W
George
,
Andrew J.
Dent
Abstract: We demonstrate a portable fs laser system, used for optical-pump Xray-probe experiments in Diamond Light Source and its application in the areas of coordination chemistry and photo-induced linkage isomerization using X-ray spectroscopy and diffraction.
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May 2025
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[24399]
Open Access
Abstract: The catalytic conversion of C–H to C–F bonds is a critical synthetic transformation of relevance to the pharmaceutical, agrochemical, and medicinal chemical industries. When coupled with an oxidant and a fluorine donor, biomimetic Mn-porphyrins have been shown to be capable of achieving this reaction. However, the definition of the active forms of these fluorinating Mn-porphyrins remains an unsolved challenge, which limits mechanistic understanding of the process and makes it challenging to systematically design better catalytic materials. Herein, we present a combination of kinetic, spectroscopic, and theoretical studies focused on alkane fluorination over Mn-containing porphyrins. Specifically, by correlating kinetic studies with resonance Raman, UV–vis, and high-energy resolution fluorescence detected X-ray absorption spectroscopic analysis of the various states of the catalyst, we provide evidence that a 6-coordinated Mn(IV) complex with −F and −OI(F)Ar axial ligands is the active species responsible for selective fluorination via Hydrogen Atom Transfer. This active state is distinct from the Mn═O species previously proposed to be the active intermediates for alkane fluorination and oxidation.
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Mar 2025
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I19-Small Molecule Single Crystal Diffraction
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Abstract: At the forefront of solid-state chemistry, single crystal to single crystal transformations (SC-SC) have been studied for many years and have grown in popularity. In this regard, solid-state molecular organometallic chemistry (SMOM-chem) is especially intriguing due to its usefulness in catalysis. SMOM systems are particularly interesting because of their capability to absorb gases which are then employed in an in-situ reaction with coordination complexes to potentially generate a new product i.e. catalysis in a single crystal. X-ray diffraction experiments can be used to investigate the adsorption capabilities of SMOM systems and uncover the precise interactions between substrate gases and their active sites. The ability of SMOM systems as well as MOF (metal-organic framework) systems to absorb gases, which are loaded into a gas cell, have been explored through X-ray diffraction. In-situ studies which lead to the extraction of kinetic information have been performed in the present study. The exact interactions between the substrate gases (Xenon, Krypton, Argon, Carbon dioxide, Hydrogen) and the crystals’ active sites have been investigated while thermodynamic and structural parameters (gas pressure, temperature, crystal size) are altered. Gas encapsulations have been monitored by detecting the changes in the crystal structure. These processes have been also modelled using Johnson- Mehl- Avrami- Kologoromov kinetics. The latest developments in the flow gas cell design and construction process undertaken in Diamond beamline I19-2 are presented.
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Mar 2025
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Abstract: Metal–organic frameworks hold immense application potential, but their stability and environmental safety remain barriers to industrial translation. Embracing the ‘safe and sustainable by design’ framework would, however, set a transformative pathway to the development of robust, recyclable metal–organic frameworks, ensuring functionality, minimal ecological impact and alignment with circular economy and chemical sustainability goals.
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Jan 2025
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B22-Multimode InfraRed imaging And Microspectroscopy
I11-High Resolution Powder Diffraction
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Yu
Han
,
Wenyuan
Huang
,
Meng
He
,
Bing
An
,
Yinlin
Chen
,
Xue
Han
,
Lan
An
,
Meredydd
Kippax-Jones
,
Jiangnan
Li
,
Yuhang
Yang
,
Mark D.
Frogley
,
Cheng
Li
,
Danielle
Crawshaw
,
Pascal
Manuel
,
Svemir
Rudic
,
Yongqiang
Chen
,
Ian
Silverwood
,
Luke L.
Daemen
,
Anibal J.
Ramirez-Cuesta
,
Sarah J.
Day
,
Stephen P.
Thompson
,
Ben F.
Spencer
,
Marek
Nikiel
,
Daniel
Lee
,
Martin
Schroeder
,
Sihai
Yang
Diamond Proposal Number(s):
[37155, 36474]
Open Access
Abstract: Capture of trace benzene is an important and challenging task. Metal–organic framework materials are promising sorbents for a variety of gases, but their limited capacity towards benzene at low concentration remains unresolved. Here we report the adsorption of trace benzene by decorating a structural defect in MIL-125-defect with single-atom metal centres to afford MIL-125-X (X = Mn, Fe, Co, Ni, Cu, Zn; MIL-125, Ti8O8(OH)4(BDC)6 where H2BDC is 1,4-benzenedicarboxylic acid). At 298 K, MIL-125-Zn exhibits a benzene uptake of 7.63 mmol g−1 at 1.2 mbar and 5.33 mmol g−1 at 0.12 mbar, and breakthrough experiments confirm the removal of trace benzene (from 5 to <0.5 ppm) from air (up to 111,000 min g−1 of metal–organic framework), even after exposure to moisture. The binding of benzene to the defect and open Zn(II) sites at low pressure has been visualized by diffraction, scattering and spectroscopy. This work highlights the importance of fine-tuning pore chemistry for designing adsorbents for the removal of air pollutants.
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Nov 2024
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[29890]
Open Access
Abstract: A key feature of coordination cages is the dynamic nature of their coordinative bonds, which facilitates the synthesis of complex polyhedral structures and their post-assembly modification. However, this dynamic nature can limit cage stability. Increasing cage robustness is important for real-world use cases. Here we introduce a double-bridging strategy to increase cage stability, where designed pairs of bifunctional subcomponents combine to generate rectangular tetratopic ligands within pseudo-cubic Zn8L6 cages. These cages withstand transmetalation, the addition of competing ligands, and nucleophilic imines, under conditions where their single-bridged congeners decompose. Our approach not only increases the stability and robustness of the cages while maintaining their polyhedral structure, but also enables the incorporation of additional functional units in proximity to the cavity. The double-bridging strategy also facilitates the synthesis of larger cages, which are inaccessible as single-bridged congeners.
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Nov 2024
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