SU-77: An Open-Framework Germanate Containing 12 × 10 × 10-Ring Channels Solved by Combining Rotation Electron Diffraction and Powder X‑ray Diffraction

A novel open-framework germanate, denoted as SU-77, was prepared by hydrothermal synthesis using ethylenediamine as the structure directing agent. The as-synthesized SU-77 is monoclinic with space group P21/a and a = 13.52427(5) Å, b = 12.64862(5) Å, c = 9.60578(3) Å, β = 92.8599(4)°. The structure of SU-77 is built from a novel Ge6O17(C2H8N2)F (Ge6) cluster building unit. The Ge6 clusters are connected to form chains along the c-axis. These chains are further connected in the [110] and [1–10] directions to form a three-dimensional framework with 12 × 10 × 10-ring channels. The as-synthesized monoclinic SU-77 became orthorhombic while being observed in a transmission electron microscope (TEM) or when heated to 200 °C in air. The orthorhombic structure of SU-77 was solved from micrometer-sized crystals by rotation electron diffraction (RED). The monoclinic structure was built from the orthorhombic structure and subsequently refined against synchrotron powder X-ray diffraction data. SU-77 is the first example of an open-framework germanate with mixed coordination polyhedra solved by electron diffraction.