Crystal Structure Solution of Radiation-Sensitive Porous Framework CL30 by Low-Dose Cryo 3D Electron Diffraction

Abstract To overcome the limitations of traditional single-crystal X-ray diffraction (SCXRD) for microcrystalline materials and the peak-overlapping issue of powder X-ray diffraction (PXRD), this study employed cryogenic continuous rotation electron diffraction (cryo-cRED) with a low-dose strategy to determine the crystal structure of CL30, a novel silicogermanate framework. It is confirmed that CL30 crystallizes in the C2/m space group and has layered topology composed of discontinuous zigzag chains connected by double four-membered ring (d4r) units, with fluoride anions (F⁻) occluded in the d4r units. In CL30, charge balance involves organic structure-directing agent (OSDA) cations, occluded F⁻, and terminal oxygen sites whose protonation state cannot be established from the present three dimensional (3D) ED data. F⁻ encapsulated in the d4r units contributes to charge compensation as the counter-anion to OSDA cations, rather than only balancing the framework charge. Although the refinement indices (R₁ = 0.29, wR₂ = 0.71) exceeded typical small-molecule crystallography standards, the structural model remained highly reliable, as supported by geometric restraints and validation. In electron diffraction, elevated R₁ values are commonly attributed to the intrinsic factors of the technique, such as dynamic scattering, detector noise from scintillator-based detectors, and TEM stage instability (large spheres of confusion). This study introduces a new structural prototype to the silicogermanate family and establishes a feasible workflow for determining the structures of radiation-sensitive microcrystalline porous materials.