Liquid-Dependent Structural Responses of a Metal-Organic Framework Revealed by Liquid-Phase Three-Dimensional Electron Diffraction.

Abstract

Liquid environments can profoundly influence the formation, structural transformation, and functional response of crystalline materials, making it essential to access their genuine structures in liquids. However, atomic-level structure analysis in liquids is highly challenging, as excessive liquid thickness, strong background scattering, and severe beam damage can severely compromise diffraction data quality. Herein, we develop a liquid-cell platform based on ultrathin carbon films. This platform confines a nanoscale local liquid layer around individual crystals and, when combined with low-dose three-dimensional electron diffraction (3D ED), enables atomic-resolution structure determination under liquid conditions. Using this approach, we achieve ab initio structure determination of a flexible metal-organic framework (MOF) Al-MIL-53 in various liquids, with data resolution reaching 0.58 Å. This allows direct revealing of two previously undiscovered solvent-dependent breathing structures in ethylene glycol and DMF, which exhibit large pore structures in contrast to the narrow pore structure observed in water. This liquid-cell platform could establish liquid-phase three-dimensional electron diffraction (LP-3DED) as an effective and widely accessible method for probing atomic-level structures in liquid environments.