Abstract
Three-dimensional electron diffraction (3DED) has been proven as an effective and accurate method for structure determination of nano-sized crystals. In the past decade, the crystal structures of various new complex metal-organic frameworks (MOFs) have been revealed by 3DED, which has been the key to understand their properties. However, due to the design of transmission electron microscopes (TEMs), one drawback of 3DED experiments is the limited tilt range of goniometers, which often leads to incomplete 3DED data, particularly when the crystal symmetry is low. This drawback can be overcome by high throughput data collection using continuous rotation electron diffraction (cRED), where data from a large number of crystals can be collected and merged. Here, we investigate the effects of improving completeness on structural analysis of MOFs. We use ZIF-EC1, a zeolitic imidazolate framework (ZIF), as an example. ZIF-EC1 crystallizes in a monoclinic system with a plate-like morphology. cRED data of ZIF-EC1 with different completeness and resolution were analyzed. The data completeness increased to 92.0% by merging ten datasets. Although the structures could be solved from individual datasets with a completeness as low as 44.5% and refined to a high precision (better than 0.04 Å), we demonstrate that a high data completeness could improve the structural model, especially on the electrostatic potential map. We further discuss the strategy adopted during data merging. We also show that ZIF-EC1 doped with cobalt can act as an efficient electrocatalyst for oxygen reduction reactions.
Highlights
The early development of 3DED techniques such as ADT/PEDT,[5,6] RED,[7,8] and EDT9 utilize stepwise rotation, where a crystal is tilted along an arbitrary axis in a transmission electron microscope (TEM), and electron diffraction (ED) patterns are collected at each angle
From the studies of the in uence of data completeness on the structural analysis of zeolitic imidazolate framework (ZIF)-EC1, we show that the structure could be solved and re ned to a high precision from continuous rotation electron diffraction (cRED) data with different completeness, even as low as 44.5% collected at various resolutions (0.70–0.93 A)
The increased data completeness led to an improved structural model
Summary
During the past two decades, three-dimensional electron diffraction (3DED) has been steadily developed as a complementary technique to single-crystal X-ray diffraction (SCXRD) for structural elucidation of nanocrystals.[1,2,3,4] The early development of 3DED techniques such as ADT/PEDT,[5,6] RED,[7,8] and EDT9 utilize stepwise rotation, where a crystal is tilted along an arbitrary axis in a transmission electron microscope (TEM), and electron diffraction (ED) patterns are collected at each angle. The structural model of ZIF-EC1 could be further improved, and peaks corresponding to atoms in the electrostatic potential map have well-de ned isotropic shapes. As ZIF-EC1 is crystallized in a monoclinic system, the individual 3DED datasets have completeness ranging from 24.1–71.6% a er the re ections were indexed using X-ray crystallography so ware package XDS 42 (Table 1).
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