Crystal structure solution of the radiation-sensitive porous framework CL30 by low-dose cryo 3D electron diffraction

To overcome the limitations of traditional single-crystal X-ray diffraction (SCXRD) for microcrystalline materials and the peak-overlapping issue of powder Xray 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 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) exceed typical small‑molecule crystallography standards, the structural model remains highly reliable, as supported by geometric restraints and validation. In electron diffraction, elevated R₁ values are commonly attributed to intrinsic factors of the technique, such as dynamic scattering, detector noise from scintillator‑based detectors, and TEM stage instability (large sphere of confusion). This work not only introduces a new structural prototype to the silicogermanate family but also establishes a feasible workflow for determining structures of radiation-sensitive microcrystalline porous materials.