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.