Electron Diffraction on Flash-Frozen Cowlesite Reveals the Structure of the First Two-Dimensional Natural Zeolite
Enrico Mugnaioli, Arianna Lanza, G. Bortolozzi, L. Righi, Marco Merlini, Valentina Cappello, Lara Marini, Athanassia Athanassiou, Mauro Gemmi
Abstract
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.