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

摘要

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 P2_1/a and a = 13.52427(5) ?, b = 12.64862(5) ?, c = 9.60578(3) ?, β = 92.8599(4)°. The structure of SU-77 is built from a novel Ge_6O_(17)(C_2H_8N_2)F (Ge_6) cluster building unit. The Ge_6 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 assynthesized monoclinic SU-77 became orthorhombic while being observed in a transmission electron microscope (TEM) or when heated to 200 ℃ 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.