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

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.