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- Wang, Yilin, et al.
(författare)
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Interrupted silicogermanate with 10-ring channels : synthesis and structure determination by combining rotation electron diffraction and powder X-ray diffraction
- 2017
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Ingår i: Inorganic Chemistry Frontiers. - 2052-1545 .- 2052-1553. ; 4:10, s. 1654-1659
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Tidskriftsartikel (refereegranskat)abstract
- Silicogermanate (JU110) with an interrupted open-framework has been synthesized by using a hydrothermal method using 1,1′-(1,4-phenylenebis(methylene))bis(1-methylpyrrolidin-1-ium) hydroxide as an organic structure-directing agent (OSDA). Silicon and fluoride anions were introduced to the concentrated-gel synthesis system, and different synthetic parameters influencing the synthesis were discussed. The structure of JU110 was characterised by using rotation electron diffraction (RED) and high-resolution powder X-ray diffraction. JU110 crystallizes in the space group Fm2m (No. 42) with a = 13.9117(2) Å, b = 18.2980(3) Å and c = 32.7800(6) Å. The structure is constructed by the sti layers found in the STI framework that are pillared by D4R/Ge7 units to form a large cavity, showing 10-ring openings along [100] and 9-ring openings along [110]. Thermal stability studies showed that the framework was maintained with the loss of water molecules, but collapsed with the removal of charge-compensating cations.
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| 3. |
- Wang, Yunchen, 1988-
(författare)
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3D Electron Diffraction : Application and Development towards High-quality Structure Determination
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electron crystallography has been proven to be effective for structure determination of nano- and micron-sized crystals. In the past few years, 3D electron diffraction (3DED) techniques were used for the structure solution of various types of complex structures such as zeolites, metal-organic frameworks (MOF) and pharmaceutical compounds. However, unlike X-ray crystallography, electron diffraction has not yet become an independent technique for a complete structure determination due to relatively poorer diffraction intensities and often powder X-ray diffraction data are used for structure validation and refinement.Electron beam damage to the structures that are sensitive to high energy electrons and dynamical scattering are important factors to lead to the deviation of electron diffraction intensities from the squared amplitudes of the structure factors. In this thesis, we investigate various aspects around the 3D electron diffraction data quality and strategies for obtaining better data and structure models. We combined 3D electron diffraction methods and powder X-ray diffraction to determine the structure of an open-framework material and discussed the difficulties and limitations of electron diffraction for beam sensitive materials. Next, we illustrated the structure determination of a pharmaceutical compound, bismuth subgallate, using 3D electron diffraction. While severe beam damage and diffuse scattering were observed in the dataset collected with the conventional rotation electron diffraction (RED) method, the continuous rotation electron diffraction (cRED) method coupled with sample cooling significantly improved the data quality and made the structure solution possible. In order to better understand the potentials and limitations of the continuous rotation method, we collected multiple datasets from different crystals of a known structure and studied the data quality by evaluating the accuracy of the refined structure models. To tackle dynamical scattering in electron diffraction data, we explored a routine for structure refinement with dynamical intensity calculation using RED data from a known structure and discussed its potentials and limitations.
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| 7. |
- Wang, Yunchen, et al.
(författare)
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On the quality of the continuous rotation electron diffraction data for accurate atomic structure determination of inorganic compounds
- 2018
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Ingår i: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 51, s. 1094-1101
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Tidskriftsartikel (refereegranskat)abstract
- The continuous rotation electron diffraction (cRED) method has the capability of providing fast three-dimensional electron diffraction data collection on existing and future transmission electron microscopes; unknown structures could be potentially solved and refined using cRED data collected from nano-and submicrometre-sized crystals. However, structure refinements of cRED data using SHELXL often lead to relatively high R1 values when compared with those refined against single-crystal X-ray diffraction data. It is therefore necessary to analyse the quality of the structural models refined against cRED data. In this work, multiple cRED data sets collected from different crystals of an oxofluoride (FeSeO3F) and a zeolite (ZSM-5) with known structures are used to assess the data consistency and quality and, more importantly, the accuracy of the structural models refined against these data sets. An evaluation of the precision and consistency of the cRED data by examination of the statistics obtained from the data processing software DIALS is presented. It is shown that, despite the high R1 values caused by dynamical scattering and other factors, the refined atomic positions obtained from the cRED data collected for different crystals are consistent with those of the reference models refined against single-crystal X-ray diffraction data. The results serve as a reference for the quality of the cRED data and the achievable accuracy of the structural parameters.
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