High-temperature electron diffraction on organic crystals: in situ crystal structure determination of Pigment Orange 34 Article Swipe
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· 2024
· Open Access
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· DOI: https://doi.org/10.1107/s2053273324096876
· OA: W4405698695
Small molecule structures and their applications rely\non good\nknowledge of their atomic arrangements. However, the crystal structures\nof these compounds and materials, which are often composed of fine\ncrystalline domains, cannot be determined with single-crystal X-ray\ndiffraction. Three-dimensional electron diffraction (3D ED) is already\nbecoming a reliable method for the structure analysis of submicrometer-sized\norganic materials. The reduction of electron beam damage is essential\nfor successful structure determination and often prevents the analysis\nof organic materials at room temperature, not to mention high temperature\nstudies. In this work, we apply advanced 3D ED methods at different\ntemperatures enabling the accurate structure determination of two\nphases of Pigment Orange 34 (C<sub>34</sub>H<sub>28</sub>N<sub>8</sub>O<sub>2</sub>Cl<sub>2</sub>), a biphenyl pyrazolone pigment that\nhas been industrially produced for more than 80 years and used for\nplastics application. The crystal structure of the high-temperature\nphase, which can be formed during plastic coloration, was determined\nat 220 °C. For the first time, we were able to observe a reversible\nphase transition in an industrial organic pigment in the solid state,\neven with atomic resolution, despite crystallites being submicrometer\nin size. By localizing hydrogen atoms, we were even able to detect\nthe tautomeric state of the molecules at different temperatures. This\ndemonstrates that precise, fast, and low-dose 3D ED measurements enable\nhigh-temperature studies the door for general <i>in situ</i> studies of nanocrystalline materials at the atomic level.
