The Structure of a Complex Open-Framework Germanate Obtained by Combining Powder Charge-Flipping and Simulated Annealing

A novel open-framework germanate, denoted as SU-74-MPMD, was prepared by hydrothermal synthesis using 2-methylpentamethylenediamine (MPMD) as the organic structure directing agent (SDA). The structure of SU-74-MPMD was determined from synchrotron X-ray powder diffraction (XRPD) data using the charge-flipping algorithm, and is one of the most complicated germanates solved from X-ray powder diffraction. The structure is built of layers of Ge₁₀O₂₆(OH)₂ (Ge₁₀) clusters that are connected by additional GeO₄ tetrahedra to form a three-dimensional (3D) framework with 10- and 12-rings. The organic structure directing agent MPMD in the pores was located by simulated annealing. SU-74-MPMD: space group <i>P</i>2₁/<i>c</i>, <i>a</i> = 12.62726(4) Å, <i>b</i> = 17.35186 (5) Å, <i>c</i> = 16.17343(5) Å, β = 115.5509(2)° and <i>Z</i> = 4. SU-74 was later synthesized using 1-(2-aminoethyl)­piperazine (AEP) as the SDA (denoted as SU-74-AEP), and its structure was solved by single crystal synchrotron X-ray diffraction. The framework structure of SU-74-AEP is the same as that of SU-74-MPMD. The locations of the organic SDAs in the pores are different for SU-74-MPMD and SU-74-AEP, suggesting a space-filling role of the SDAs. The Ge₁₀ clusters follow the <b>fcu</b>-11-<i>P</i>2₁/<i>c</i> net. The underlying topology of SU-74 is compared to those of other Ge₁₀ structures containing additional GeO₄ tetrahedra. The presence of additional tetrahedra can significantly affect the framework topology through the addition of edges between the Ge₁₀ nodes