Crystalline Sponge Method by Three-Dimensional Electron Diffraction.

Pohua Chen,Chaochao Zhang,Leifeng Liu,Junliang Sun,Yang Liu,Fei Huang

doi:10.3389/fmolb.2021.821927

Abstract

The crystalline sponge method has shown to be a novel strategy for the structure determination of noncrystalline, oily, or trace amount of a compound. A target compound was absorbed and oriented orderly in the pregrown porous crystal for x-ray diffraction analysis. However, the diffusion in the micron-sized crystals is rather difficult. Lots of trial-and-error experiments are needed to optimize the guest-soaking process and to improve data quality. Nanocrystals are better in diffusion, yet it could not conduct a single crystal x-ray diffraction (SCXRD) analysis. Three-dimensional electron diffraction (3D-ED) is a powerful diffraction tool for the structure determination of small crystals. In this work, we successfully carried out the crystalline sponge method by 3D-ED technique using {(ZnI2)3-[2,4,6-tris(4-pyridyl)-1,3,5-triazine]2·x(guest)}n (1-Guest) porous complex nanocrystals. On account of the better diffuse ability of nanocrystals, the time needed for solvent exchange and guest soaking protocols are shortened 50-fold faster versus the original protocol. The crystal structure of the crystalline sponge incorporated with three different guests was fully resolved using a merged dataset. The structure model was identical to previously reported ones using x-ray, showing that the accuracy of the 3D-ED was comparable with SCXRD. The refinement results can also give the precise occupancy of the guest molecule soaked in the porous crystal. This work not only provides a new data collection strategy for crystalline sponge method but also demonstrates the potential of 3D-ED techniques to study host-guest interaction by solving the fine structure of porous material.

Highlights

A molecular structure of a substance determines its intrinsic properties, such as reactivity, stereochemistry selectivity, etc
We demonstrate the crystalline sponge method using the 3D-ED technique with nanosized crystalline sponge” (CS) crystal
Instead of the large crystals used in the traditional CS method, we are more interested about the powder-like crystals at the bottom of the synthesis liquid

Summary

Introduction

A molecular structure of a substance determines its intrinsic properties, such as reactivity, stereochemistry selectivity, etc. Chemists have developed nuclear magnetic resonance spectroscopy (NMR) and mass spectroscopy (MS) to provide essential structural information, but there are still chances to assign the structure incorrectly. Single-crystal x-ray diffraction (SCXRD) is the standard method that provides a direct three-dimensional structure at the atomic level. The major limitation of SCXRD is that it requires the target compound to crystallize into a single crystal with sufficient quality and size (>5 μm × 5 μm × 5 μm). To address the challenge of structure determination on noncrystalline samples, Fujita and coworkers reported the “crystalline sponge” (CS) method (Inokuma et al, 2013; Hoshino et al, 2016). The CSs are porous crystalline materials that can absorb molecules in the solution and enable

Methods

Results

Conclusion