Electron Diffraction on Flash-Frozen Cowlesite Reveals the Structure of the First Two-Dimensional Natural Zeolite

Abstract

Cowlesite, ideally Ca 6 Al 12 Si 18 O 60 ·36H 2 O, is to date the only natural zeolite whose structure could not be determined by X-ray methods. In this paper, we present the ab initio structure determination of this mineral obtained by three-dimensional (3D) electron diffraction data collected from single-crystal domains of a few hundreds of nanometers. The structure of cowlesite consists of an alternation of rigid zeolitic layers and low-density interlayers supported by water and cations. This makes cowlesite the only two-dimensional (2D) zeolite known in nature. When cowlesite gets in contact with a transmission electron microscope vacuum, a phase transition to a conventional 3D zeolite framework occurs in few seconds. The original cowlesite structure could be preserved only by adopting a cryo-plunging sample preparation protocol usually employed for macromolecular samples. Such a protocol allows the investigation by 3D electron diffraction of very hydrated and very beam-sensitive inorganic materials, which were previously considered intractable by transmission electron microscopy crystallographic methods.

Three-dimensional electron diffraction for porous crystalline materials: structural determination and beyond

“…In addition to structure determination of novel zeolites, 3DED has also made it possible to determine structures of zeolites that remained unsolved for decades. For example, the structures of two aluminosilicates ZSM-43 63 and ZSM-25, 64 and a 2D natural zeolite cowlesite 65 were solved from 3DED data after remaining elusive for more than 30 years. The structures of ZSM-43 and cowlesite were solved from high-resolution (∼1.0 Å) data by direct methods.…”

Krupičkaite, Cu6[AsO3(OH)]6·8H2O, a new copper arsenate mineral from Jáchymov (Czech Republic)

“…This is also associated with very strong diffuse features in the data that hamper a reliable structural analysis. The cryo-plunging method, initially used for organic and biological samples, was recently applied to inorganic samples (Mugnaioli et al 2020;Steciuk et al 2020;Steciuk et al 2021). To collect 3D electron diffraction (3D ED) data on single crystals (Gemmi and Lanza 2019), the precession electron diffraction tomography (PEDT) technique was used (Vincent and Midgley 1994; Kolb et al 2007Kolb et al , 2008Mugnaioli et al 2009).…”

Refinements on electron diffraction data of β-glycine in MoPro: a quest for an improved structure model

“…A new technique, electron cryo-microscopy (cryo-EM), has taken a leap in the past few years. The cryo-EM method known as 3D electron diffraction (3D ED) has also been reported to provide atomic resolution structures of various small molecules, pharmaceutically active mixtures, zeolites, metal organic frameworks and macromolecules (Nannenga et al, 2014;Yonekura et al, 2015;van Genderen et al, 2016;Gemmi et al, 2019;Gruene et al, 2018;Jones et al, 2018;Mugnaioli et al, 2020;Beale et al, 2020). 3D ED data are collected by rotating the crystal inside a transmission electron microscope.…”