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Instruments / Technical Area	Publication Details	Published
	Watching photochemistry happen: Recent developments in dynamic single-crystal X-ray diffraction studies Lauren E. Hatcher , Mark R. Warren , Anuradha R. Pallipurath , Lucy Saunders , Jonathan M. Skelton DOI: 10.1007/430_2020_78 Show Abstract ▼ Abstract: Photoresponsive materials are an important contemporary research area with applications in, for example, energy and catalysis. Mechanistic information on solid-state photochemical reactions has traditionally come from spectroscopy and modelling, with crystallography limited to snapshots of endpoints and long-lived intermediates. Recent advances in X-ray sources and detectors have made it possible to follow solid-state reactions in situ with dynamic single-crystal X-ray diffraction (SCXRD) methods, allowing a full set of atomic positions to be determined over the course of the reaction. These experiments provide valuable structural information that can be used to interpret spectroscopic measurements and to inform materials design and optimisation. Solid-state linkage isomers, where small-molecule ligands such as NO, NO2−, N2 and SO2 show photo-induced changes in binding to a transition metal centre, have played a leading role in the development of dynamic SCXRD methodology, since the movement of whole atoms and the predictable temperature dependence of the excited-state lifetimes make them ideal test systems. The field of “photocrystallography”, pioneered by Coppens in the late 1990s, has developed alongside advances in instrumentation and computing and can now provide the 3D structures of species with lifetimes down to femtoseconds. In this chapter, we will review the development of photocrystallography experiments against linkage isomer systems, from the early identification of metastable species under continuous illumination, through measuring kinetics at low temperature, to recent experiments studying species with sub-second lifetimes. We will discuss the advances in X-ray sources and instrumentation that have made dynamic SCXRD experiments possible, and we will highlight the role of kinetic modelling and complementary spectroscopy in designing experiments. Finally, we will discuss possible directions for future development and identify some of the outstanding challenges that remain to be addressed.	Oct 2020
	Chemical trends in the lattice thermal conductivity of Li(Ni, Mn, Co)O2 (NMC) battery cathodes Hui Yang , Christopher N. Savory , Benjamin J. Morgan , David O. Scanlon , Jonathan M. Skelton , Aron Walsh Chemistry Of Materials DOI: 10.1021/acs.chemmater.0c02908 Show Abstract ▼ Abstract: While the transport of ions and electrons in conventional Li-ion battery cathode materials is well understood, our knowledge of the phonon (heat) transport is still in its infancy. We present a first-principles theoretical investigation of the chemical trends in the phonon frequency dispersion, mode lifetimes, and thermal conductivity in the series of layered lithium transition-metal oxides Li(NixMnyCoz)O2 (x + y + z = 1). The oxidation and spin states of the transition metal cations are found to strongly influence the structural dynamics. Calculations of the thermal conductivity show that LiCoO2 has highest average conductivity of 45.9 W·m–1·K–1 at T = 300 K and the largest anisotropy, followed by LiMnO2 with 8.9 W·m–1·K–1 and LiNiO2 with 6.0 W·m–1·K–1. The much lower thermal conductivity of LiMnO2 and LiNiO2 is found to be due to 1–2 orders of magnitude shorter phonon lifetimes. We further model the properties of binary and ternary transition metal combinations to examine the possible effects of mixing on the thermal transport. These results serve as a guide to ongoing work on the design of multicomponent battery electrodes with more effective thermal management.	Aug 2020
I09-Surface and Interface Structural Analysis	Sn 5s2 lone pairs and the electronic structure of tin sulphides: A photoreflectance, high-energy photoemission, and theoretical investigation Leanne A. H. Jones , Wojciech M. Linhart , Nicole Fleck , Jack E. N. Swallow , Philip A. E. Murgatroyd , Huw Shiel , Thomas J. Featherstone , Matthew J. Smiles , Pardeep K. Thakur , Tien-lin Lee , Laurence J. Hardwick , Jonathan Alaria , Frank Jaeckel , Robert Kudrawiec , Lee A. Burton , Aron Walsh , Jonathan M. Skelton , Tim D. Veal , Vin R. Dhanak Physical Review Materials 4 DOI: 10.1103/PhysRevMaterials.4.074602 Diamond Proposal Number(s): [21431] Open Access Show Abstract ▼ Abstract: The effects of Sn 5 s lone pairs in the different phases of Sn sulphides are investigated with photoreflectance, hard x-ray photoemission spectroscopy (HAXPES), and density functional theory. Due to the photon energy-dependence of the photoionization cross sections, at high photon energy, the Sn 5 s orbital photoemission has increased intensity relative to that from other orbitals. This enables the Sn 5 s state contribution at the top of the valence band in the different Sn-sulphides, SnS, Sn 2 S 3 , and SnS 2 , to be clearly identified. SnS and Sn 2 S 3 contain Sn(II) cations and the corresponding Sn 5 s lone pairs are at the valence band maximum (VBM), leading to ∼ 1.0 –1.3 eV band gaps and relatively high VBM on an absolute energy scale. In contrast, SnS 2 only contains Sn(IV) cations, no filled lone pairs, and therefore has a ∼ 2.3 eV room-temperature band gap and much lower VBM compared with SnS and Sn 2 S 3 . The direct band gaps of these materials at 20 K are found using photoreflectance to be 1.36, 1.08, and 2.47 eV for SnS, Sn 2 S 3 , and SnS 2 , respectively, which further highlights the effect of having the lone-pair states at the VBM. As well as elucidating the role of the Sn 5 s lone pairs in determining the band gaps and band alignments of the family of Sn-sulphide compounds, this also highlights how HAXPES is an ideal method for probing the lone-pair contribution to the density of states of the emerging class of materials with n s 2 configuration.	Jul 2020
	Highly anisotropic thermal transport in LiCoO2 Hui Yang , Jia-yue Yang , Christopher N. Savory , Jonathan M. Skelton , Benjamin J. Morgan , David O. Scanlon , Aron Walsh The Journal Of Physical Chemistry Letters DOI: 10.1021/acs.jpclett.9b02073 Show Abstract ▼ Abstract: LiCoO2 is the prototypical cathode in lithium-ion batteries. Its crystal structure consists of Li+ and CoO2– layers that alternate along the hexagonal ⟨0001⟩ axis. It is well established that the ionic and electronic conduction are anisotropic, but little is known regarding the heat transport. We analyze the phonon dispersion and lifetimes using anharmonic lattice dynamics based on quantum-chemical force constants. Around room temperature, the thermal conductivity in the hexagonal ab plane of the layered cathode is ∼6 times higher than that along the c axis. An upper limit to the average thermal conductivity at T = 300 K of 38.5 W m–1 K–1 is set by short phonon lifetimes associated with anharmonic interactions within the octahedral face-sharing CoO2– network. Observations of conductivity <10 W m–1 K–1 can be understood by additional scattering channels including grain boundaries in polycrystalline samples. The impact on thermal processes in lithium-ion batteries is discussed.	Sep 2019
I19-Small Molecule Single Crystal Diffraction	Monitoring Photo-induced Population Dynamics in Metastable Linkage Isomer Crystals: A Crystallographic Kinetic Study of [Pd(Bu4dien)NO2]BPh4 Lauren E. Hatcher , Jonathan M. Skelton , Mark R. Warren , Clare Stubbs , Estelina Lora Da Silva , Paul R. Raithby Physical Chemistry Chemical Physics DOI: 10.1039/C7CP05422J Diamond Proposal Number(s): [8567, 9734, 13698] Open Access Show Abstract ▼ Abstract: We present a detailed kinetic study of photo-induced solid state linkage isomerism in the compound [Pd(Bu4dien)NO2]BPh4 (Bu4dien = N,N,N’,N’-tetrabutyldiethylenetriamine) using in-situ photocrystallographic techniques. We explore the key variables that influence the photoconversion and develop a detailed kinetic model for the excitation and decay processes and the temperature dependence of the conversion rates. We show that by varying the temperature the lifetime of the excited state can be varied over orders of magnitude, making these systems ideal test cases for the development of new time-resolved X-ray diffraction methods. The kinetic model is used to build a numerical-simulation tool, which we use to explore the practicalities of pump-probe single-crystal diffraction experiments with minute and second time-resolution.	Jan 2018
I24-Microfocus Macromolecular Crystallography	A rapidly-reversible absorptive and emissive vapochromic Pt(II) pincer-based chemical sensor M. J. Bryant , J. M. Skelton , L. E. Hatcher , C. Stubbs , E. Madrid , A. R. Pallipurath , L. H. Thomas , Ch. H. Woodall , J. Christensen , S. Fuertes , T. P. Robinson , C. M. Beavers , S. J. Teat , M. Warren , F. Pradaux-caggiano , A. Walsh , F. Marken , D. R. Carbery , S. C. Parker , N. B. Mckeown , R. Malpass-evans , M. Carta , P. R. Raithby Nature Communications 8 DOI: 10.1038/s41467-017-01941-2 Open Access Show Abstract ▼ Abstract: Selective, robust and cost-effective chemical sensors for detecting small volatile-organic compounds (VOCs) have widespread applications in industry, healthcare and environmental monitoring. Here we design a Pt(II) pincer-type material with selective absorptive and emissive responses to methanol and water. The yellow anhydrous form converts reversibly on a subsecond timescale to a red hydrate in the presence of parts-per-thousand levels of atmospheric water vapour. Exposure to methanol induces a similarly-rapid and reversible colour change to a blue methanol solvate. Stable smart coatings on glass demonstrate robust switching over 104 cycles, and flexible microporous polymer membranes incorporating microcrystals of the complex show identical vapochromic behaviour. The rapid vapochromic response can be rationalised from the crystal structure, and in combination with quantum-chemical modelling, we provide a complete microscopic picture of the switching mechanism. We discuss how this multiscale design approach can be used to obtain new compounds with tailored VOC selectivity and spectral responses.	Dec 2017
I19-Small Molecule Single Crystal Diffraction	Observation of a re-entrant phase transition in the molecular complex tris(μ 2 -3,5-diisopropyl-1,2,4-triazolato-κ 2 N 1 : N 2 )trigold(I) under high pressure Christopher H. Woodall , Jeppe Christensen , Jonathan M. Skelton , Lauren E. Hatcher , Andrew Parlett , Paul R. Raithby , Aron Walsh , Stephen C. Parker , Christine M. Beavers , Simon J. Teat , Mourad Intissar , Christian Reber , David R. Allan Iucrj 3, 367 - 376 DOI: 10.1107/S2052252516013129 Open Access Show Abstract ▼ Abstract: We report a molecular crystal that exhibits four successive phase transitions under hydrostatic pressure, driven by aurophilic interactions, with the ground-state structure re-emerging at high pressure. The effect of pressure on two polytypes of tris(μ2-3,5-diisopropyl-1,2,4-triazolato-κ2N1:N2)trigold(I) (denoted Form-I and Form-II) has been analysed using luminescence spectroscopy, single-crystal X-ray diffraction and first-principles computation. A unique phase behaviour was observed in Form-I, with a complex sequence of phase transitions between 1 and 3.5 GPa. The ambient C2/c mother cell transforms to a P21/n phase above 1 GPa, followed by a P21/a phase above 2 GPa and a large-volume C2/c supercell at 2.70 GPa, with the previously observed P21/n phase then reappearing at higher pressure. The observation of crystallographically identical low- and high-pressure P21/n phases makes this a rare example of a re-entrant phase transformation. The phase behaviour has been characterized using detailed crystallographic theory and modelling, and rationalized in terms of molecular structural distortions. The dramatic changes in conformation are correlated with shifts of the luminescence maxima, from a band maximum at 14040 cm−1 at 2.40 GPa, decreasing steeply to 13550 cm−1 at 3 GPa. A similar study of Form-II displays more conventional crystallographic behaviour, indicating that the complex behaviour observed in Form-I is likely to be a direct consequence of the differences in crystal packing between the two polytypes.	Sep 2016
I19-Small Molecule Single Crystal Diffraction	Sulfamerazine: Understanding the Influence of Slip Planes in the Polymorphic Phase Transformation through X-Ray Crystallographic Studies and ab Initio Lattice Dynamics Anuradha R. Pallipurath , Jonathan M. Skelton , Mark R. Warren , Naghmeh Kamali , Patrick Mcardle , Andrea Erxleben Molecular Pharmaceutics 12 (10), 3735 - 3748 DOI: 10.1021/acs.molpharmaceut.5b00504 PMID: 26317333 Show Abstract ▼ Abstract: Understanding the polymorphism exhibited by organic active-pharmaceutical ingredients (APIs), in particular the relationships between crystal structure and the thermodynamics of polymorph stability, is vital for the production of more stable drugs and better therapeutics, and for the economics of the pharmaceutical industry in general. In this article, we report a detailed study of the structure–property relationships among the polymorphs of the model API, Sulfamerazine. Detailed experimental characterization using synchrotron radiation is complemented by computational modeling of the lattice dynamics and mechanical properties, in order to study the origin of differences in millability and to investigate the thermodynamics of the phase equilibria. Good agreement is observed between the simulated phonon spectra and mid-infrared and Raman spectra. The presence of slip planes, which are found to give rise to low-frequency lattice vibrations, explains the higher millability of Form I compared to Form II. Energy/volume curves for the three polymorphs, together with the temperature dependence of the thermodynamic free energy computed from the phonon frequencies, explains why Form II converts to Form I at high temperature, whereas Form III is a rare polymorph that is difficult to isolate. The combined experimental and theoretical approach employed here should be generally applicable to the study of other systems that exhibit polymorphism.	Oct 2015

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