Structural and Electronic Effects of X-ray Irradiation on Prototypical [M(COD)Cl]2 Catalysts

Lattice response to the radiation damage of molecular crystals: radiation-induced versus thermal expansivity

The interaction of intense synchrotron radiation with molecular crystals frequently modifies the crystal structure by breaking bonds, producing fragments and, hence, inducing disorder. Here, a second-rank tensor of radiation-induced lattice strain is proposed to characterize the structural susceptibility to radiation. Quantitative estimates are derived using a linear response approximation from experimental data collected on three materials Hg(NO3)2(PPh3)2, Hg(CN)2(PPh3)2 and BiPh3 [PPh3 = triphenylphosphine, P(C6H5)3; Ph = phenyl, C6H5], and are compared with the corresponding thermal expansivities. The associated eigenvalues and eigenvectors show that the two tensors are not the same and therefore probe truly different structural responses. The tensor of radiative expansion serves as a measure of the susceptibility of crystal structures to radiation damage.

XPS and HR TEM Elucidation of the Diversity of Titania-Supported Single-Site Ir Catalyst Performance in Spin-Selective Propene Hydrogenation

Immobilized [Ir(COD)Cl]2-Linker/TiO2 catalysts with linkers containing Py, P(Ph)2 and N(CH3)2 functional groups were prepared. The catalysts were tested via propene hydrogenation with parahydrogen in a temperature range from 40 °C to 120 °C which was monitored via NMR. The catalytic behavior of [Ir(COD)Cl]2-Linker/TiO2 is explained on the basis of quantitative and qualitative XPS data analysis performed for the catalysts before and after the reaction at 120 °C. It is shown that the temperature dependence of propene conversion and the enhancement of the NMR signal are explained via a combination of the stabilities of both the linker and immobilized [Ir(COD)Cl]2 complex. It is demonstrated that the N(CH3)2-linker is the most stable at the surface of TiO2 under used reaction conditions. As a result, only this sample shows a rise in the enhancement of the NMR signal in the 100-120 °C temperature range.

Radiation damage to biological macromolecules∗

In this review, we describe recent research developments into radiation damage effects in macromolecular X-ray crystallography observed at synchrotrons and X-ray free electron lasers. Radiation damage in small molecule X-ray crystallography, small angle X-ray scattering experiments, microelectron diffraction, and single particle cryo-electron microscopy is briefly covered.

Variability in X-ray induced effects in [Rh(COD)Cl]2 with changing experimental parameters

X-ray characterisation methods have undoubtedly enabled cutting-edge advances in all aspects of materials research. Despite the enormous breadth of information that can be extracted from these techniques, the challenge of radiation-induced sample change and damage remains prevalent. This is largely due to the emergence of modern, high-intensity X-ray source technologies and the growing potential to carry out more complex, longer duration in situ or in operando studies. The tunability of synchrotron beamlines enables the routine application of photon energy-dependent experiments. This work explores the structural stability of [Rh(COD)Cl]₂, a widely used catalyst and precursor in the chemical industry, across a range of beamline parameters that target X-ray energies of 8 keV, 15 keV, 18 keV and 25 keV, on a powder X-ray diffraction synchrotron beamline at room temperature. Structural changes are discussed with respect to absorbed X-ray dose at each experimental setting associated with the respective photon energy. In addition, the X-ray radiation hardness of the catalyst is discussed, by utilising the diffraction data collected at the different energies to determine a dose limit, which is often considered in protein crystallography and typically overlooked in small molecule crystallography. This work not only gives fundamental insight into how damage manifests in this organometallic catalyst, but will encourage careful consideration of experimental X-ray parameters before conducting diffraction on similar radiation-sensitive organometallic materials.

Radiation effects, zero thermal expansion, and pressure-induced phase transition in CsMnCo(CN)6

The Prussian blue analogue CsMnCo(CN)₆ is studied using powder X-ray and neutron diffraction under variable temperature, pressure, and X-ray exposure. It retains cubic F4̄3m symmetry in the range 85-500 K with minimal thermal expansion, whereas a phase transition to P4̄n2 occurs at ∼2 GPa, driven by octahedral tilting. A small lattice contraction occurs upon increased X-ray dose. Comparisons with related systems indicate that the Cs^I ions decrease the thermal expansion and suppress the likelihood of phase transformations. The results improve the understanding of the stimuli-responsive behaviour of coordination polymers.

Effect of synchrotron X-ray radiation damage on phase transitions in coordination polymers at high pressure

The high-pressure phase-transition behaviour of metal-organic frameworks and coordination polymers upon varying degrees of X-ray irradiation are highlighted with four example studies. These show that, in certain cases, the radiation damage, while not extreme in changing unit-cell values, can impact the existence of a phase transition. In particular, pressure-induced phase transitions are suppressed after a certain absorbed dose threshold is reached for the sample. This is thought to be due to partial amorphization and/or defect formation in the sample, hindering the co-operative structural distortions needed for a phase transition. The high-pressure experiments were conducted with several crystals within the sample chamber in order to measure crystals with minimal X-ray irradiation at the highest pressures, which are compared with the crystals measured continuously upon pressure increase. Ways to minimize radiation damage are also discussed within the frame of high-pressure experiments.

Radiation damage to biological samples: still a pertinent issue

An understanding of radiation damage effects suffered by biological samples during structural analysis using both X-rays and electrons is pivotal to obtain reliable molecular models of imaged molecules. This special issue on radiation damage contains six papers reporting analyses of damage from a range of biophysical imaging techniques. For X-ray diffraction, an in-depth study of multi-crystal small-wedge data collection single-wavelength anomalous dispersion phasing protocols is presented, concluding that an absorbed dose of 5 MGy per crystal was optimal to allow reliable phasing. For small-angle X-ray scattering, experiments are reported that evaluate the efficacy of three radical scavengers using a protein designed to give a clear signature of damage in the form of a large conformational change upon the breakage of a disulfide bond. The use of X-rays to induce OH radicals from the radiolysis of water for X-ray footprinting are covered in two papers. In the first, new developments and the data collection pipeline at the NSLS-II high-throughput dedicated synchrotron beamline are described, and, in the second, the X-ray induced changes in three different proteins under aerobic and low-oxygen conditions are investigated and correlated with the absorbed dose. Studies in XFEL science are represented by a report on simulations of ultrafast dynamics in protic ionic liquids, and, lastly, a broad coverage of possible methods for dose efficiency improvement in modalities using electrons is presented. These papers, as well as a brief synopsis of some other relevant literature published since the last Journal of Synchrotron Radiation Special Issue on Radiation Damage in 2019, are summarized below.