30 31 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 2 / 2 3 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 2 / 2 3 NewNEXAFS beamline rapidly characterises bonds in non- crystallinematerials Physical Chemistry – Technique development – Chemistry Drugs are commonly manufactured in the form of tablets that contain other materials. The role of these additional ingredients is to ensure that drug release in the body is controlled, with just the right dose over a defined amount of time. There is a lot of interest in the idea of manufacturing the drug itself by crystallisation with a second ingredient, giving access to drug release profiles that cannot be achieved through tablet formulation. The products of crystallisation with a second component are typically held together by electrostatic bonds associated with the sharing of hydrogen atoms between the two components. Such bonds are called hydrogen bonds. Often, the hydrogen nucleus separates from its electron and forms an ionic bond, and the resulting product is called a salt. Clarity about which type of bonding occurs is essential for predictive modelling of properties ( e.g. for designing a drug release profile), as well as for regulatory approval and patenting of the resulting medicine. Traditionally, crystal structureanalysis byX-raydiffraction (crystallography) has been used to classify products into co-crystals and salts. Crystallography relies on locating the position of the hydrogen in the crystal structure precisely, which can be a challenge because hydrogen is an extremely weak X-ray scatterer. Diamond and the University of Leeds partnered to develop the new high- throughput Near-Edge X-ray Absorption Fine-Structure (NEXAFS) spectroscopy end station at the B07 beamline. The team then used it to characterise three 2-component systems to examine whether the sensitivity of NEXAFS to the hydrogen position is sufficient to identify the nature of the intermolecular bond. The NEXAFS spectra classified the hydrogen donor-acceptor products unequivocally into salts and co-crystals, and even identified that some of the interactions placed the materials on the boundary between salts and co- crystals. As NEXAFS does not require a crystalline form of a sample, this study opens up NEXAFS to characterising hydrogen donor-acceptor interactions in other forms of matter: solutions, melts, thin films, and amorphous materials. The high-throughput NEXAFS capability of the new B07 beamline facilitates the characterisation of local bonding in organic crystal structures on timescales of minutes. This technique is relevant for a wide range of materials beyond the pharmaceutical context of this work; solar energy conversion, energy storage in batteries, fuel cell power and formulated consumer products ( e.g. foods and household products such as cleaners) involve hydrogen bonding and proton transfer in non-crystalline matter. The capability to identify these interactions quickly and correctly will be an invaluable aid in the development of new technologies and products. Related publication: Edwards, PT. et al. Determination of H-atom positions in organic crystal structures by NEXAFS combined with density functional theory: a study of two-component systems containing isonicotinamide. The Journal of Physical Chemistry A 126 , 19 (2022): 2889-2898. DOI: 10.1021/acs.jpca.2c00439 Funding acknowledgement: EPSRC and Diamond Light Source: PhD studentship (EPSRC Grant EP/ R513258/1) EPSRC Grant (EP/P006965/1) Corresponding authors: Sven L M Schroeder, University of Leeds,
[email protected] Elizabeth Shotton, Diamond Light Source,
[email protected] Structures and Surfaces Group Beamline B07-B For nitrogen atoms involved in a hydrogen bond, the X-ray photon energy required for a resonant excitation of its 1s electron decreased linearly with the distance to the hydrogen atom. Using resonant X-ray Photoelectron Spectroscopy to understand the reactivity of ionic liquids Physical Chemistry – Technique Development - Chemistry In numerous applications that involve electron donation in a liquid environment, such as electrochemical energy storage and catalysis, a comprehensive understanding of the occupied electronic states is essential to understand and predict reactivity. However, although many theories exist relating electronic structure to reactivity, they have often not been rigorously tested against experimental data. This is especially challenging for solutes in liquids, because the electronic structure of the liquid phase is very hard to measure. An international team of researchers planned to investigate the electronic structure of both solvents and solutes in solvents. They wanted to explore the limits of the synchrotron technique resonant X-ray Photoelectron Spectroscopy (resonant XPS), which they believe is underused, especially when applied to solvents and solutes dissolved in solvents. These investigations represent a continuation of previous work by the group on Diamond’s B07 beamline (Seymour et al. , Phys. Chem. Chem. Phys., 2021, 23, 20957), and were carried out on B07-C, the Ambient Pressure (AP) XPS end station. B07-C is ideal for studying ionic liquid samples. Ionic liquids are made up solely of ions and have very low volatility, which means they can be studied as liquid drops on B07-C XPS. Resonant XPS requires tuneable X-ray energies, which cannot be accessed on lab XPS apparatus. Simple calculations often capture the electronic structure of the solvents and solutes in solvents, but are not always accurate. For example, the team found they needed more complex calculations to satisfactorily model the cobalt-containing sample studied on B07. The mismatch is caused by unpaired electrons in the cobalt complex; these unpaired electrons give rise to very useful reactivity, but also provide challenges for theory. Ionic liquids (ILs) are liquid salts made only of positively and negatively charged ions and have a unique combination of properties. ILs are liquid at room temperature, whereas NaCl (common table salt) has a melting point of approximately 1000 K. ILs conduct electricity and decompose before they boil, unlike molecular liquids. These incredible properties mean that there is enormous potential for the use of ILs in electrochemical energy storage devices, e.g. batteries for phones and supercapacitors for cars. For electrochemical energy storage devices, determining what happens when ILs are subjected to potential ( i.e. electrical energy) is paramount. When the voltage is outside the safe operating range, the IL will decompose, and the device will malfunction. Therefore, the ILs have a voltage operating range, which is analogous to the operating temperature range of people - at high and low temperatures, people malfunction. The factors that control the operating range are very complicated. The results are very useful in understanding how to extend the operating range of ILs used in applications, by linking the electronic data to theory and calculations. The team has since recorded further results on B07 and is working on testing which theories capture the experimental results recorded. Related publication: Seymour, JM. et al. Resonant X-ray photoelectron spectroscopy: identification of atomic contributions to valence states. Faraday Discussions 236 , 389-411 (2022) DOI: 10.1039/D1FD00117E Funding acknowledgement: Royal Society University Research Fellowship (URF\R\150353) Royal Society University Research Fellowship Enhancement Award (RGF\ EA\180089). Royal Society Research Grant for Research Fellows (RGF\R1\180053) Emmy-Noether grant (DFG, SE 2253/3-1) Corresponding author: Kevin Lovelock, University of Reading,
[email protected] Structures and Surfaces Group Beamline B07-C Co 2p 3/2 resonant X-ray Photoelectron Spectroscopy heat map for the tetrachlorocobaltate anion [CoCl 4 ] 2- . The brown/white features capture the energy of the reactive electrons located near to the cobalt atom in the [CoCl 4 ] 2- anion, with a pictorial representation of a molecular orbital depicting calculated electron location also shown.