Maximizing completeness in single-crystal high-pressure diffraction experiments: phase transitions in 2°AP

Abstract

Sufficiently high completeness of diffraction data is necessary to correctly determine the space group, observe solid-state structural transformations or investigate charge density distribution under pressure. Regrettably, experiments performed at high pressure in a diamond anvil cell (DAC) yield inherently incomplete datasets. The present work systematizes the combined influence of radiation wavelength, DAC opening angle and sample orientation in a DAC on the completeness of diffraction data collected in a single-crystal high-pressure (HP) experiment with the help of dedicated software. In particular, the impact of the sample orientation on the achievable data completeness is quantified and proved to be substantial. Graphical guides for estimating the most beneficial sample orientation depending on the sample Laue class and assuming a few commonly used experimental setups are proposed. The usefulness of these guides has been tested in the case of luminescent 1,3-diacetylpyrene, suspected to undergo transitions from the α phase (Pnma) to the γ phase (Pn21 a) and δ phase (P1121/a) under pressure. Effective sample orientation has ensured over 90% coverage even for the monoclinic system and enabled unrestrained structure refinements and access to complete systematic extinction patterns.

Tracking structural phase transitions via single crystal x-ray diffraction at extreme conditions: advantages of extremely brilliant source

“…(a) Crystal pre-orientation (b) Loading more than one crystal in different orientations (c) Irradiation with shorter wavelength (larger Ewald sphere = lager accessible region) (d) Optimized collection strategy (scanning between many limiting positions), well executed with four-circle diffractometers Recently, a custom-made Python3 library was released, in order to calculate the best crystal orientation in DAC for the maximum data coverage [26]. Synchrotrons benefit from the tuneable x-ray wavelength, but usually the data collection strategy is limited to a simple ω-scan, due to geometrical constraints of the heavy-duty goniometers.…”

Pressure-Induced Coordination Number Transition in Lanthanide Mellitate Coordination Polymers: Structure and Spectroscopy

“…Although high-pressure structural studies of coordination complexes are scant, especially for f-elements, due to the difficulties associated with the sample being enclosed in a diamond anvil cell (DAC), there has been recent interest and advances in using high-pressure crystallographic techniques to characterize pressure-induced structural changes. − In some cases, computational structural optimizations within theoretical or experimental unit cell parameters have been used to predict changes in bond distances; , however, with specially designed DACs having a compact form and large opening angles, it is possible to obtain crystal structures at elevated pressures. , Due to the nature of this process, high-pressure SCXRD data typically suffer from low completeness and redundancy; however, with careful set-up and processing of data, it is possible to acquire meaningful results. − In this paper, we present the high-pressure SCXRD characterization of a cerium mellitate coordination polymer and measurement of the metal–ligand bond length changes as well as an unexpected coordination number transition.…”

Confirmation of Phase Transitions and Laser-Assisted Chemical Reaction for Pyridine under High Pressure

“…Recently, research interest in the properties of molecular crystals under high pressure has continued to rise. , External high pressure reduces intermolecular distances, enhances intermolecular and intramolecular interactions, modifies properties, and induces structure phase transformation in molecular crystals . High-pressure research methods typically include both experimental and computational components. − The experimental method based on diamond anvil cells (DAC) generates a high-pressure environment for a sample and can provide the evolution of phase transitions, atomic coordinates, and unit cell parameters of molecular crystals, combined with synchrotron XRD, Raman and infrared spectroscopy, photoluminescence, etc. − Computational methods, including density functional theory (DFT) − and force field (FF) groups, can provide the energetic characteristics of investigated materials and explain the nature of phase transitions on the basis of the critical parameters from experimental measurements for molecular crystals. , Significant progress in engineering made these experiments possible and even routine in some sense, but they were still very time-consuming and complicated. These experiments give the atomic coordinates and cell parameters of molecular crystals.…”