Complex Open-Framework Germanate Built by 8‑Coordinated Ge₁₀ Clusters

A novel open-framework germanate |(C₅H₁₄­N₂)₂­(C₅H₁₂­N₂)_0.5(H₂O)_2.5|[Ge_12.5O₂₆(OH)₂] with three-dimensional 10- and 11-ring channels, denoted as SU-67, has been synthesized under hydrothermal conditions using 2-methylpiperazine (MPP) as the structure-directing agent (SDA). The synthesis is intimately related to that of JLG-5, a tubular germanate built from Ge₇ clusters. The influences of synthesis parameters are discussed. A strong influence of the hydrofluoric acid quantity on the resulting cluster building units can be concluded. The framework of SU-67 is based on an elaborate topological pattern of connected Ge₁₀ clusters forming intersecting 10- and 11-ring channels and has a low framework density (12.4 Ge atoms per 1000 ų). We have discovered that the topology of SU-67 is a new 8-connected nce-8-I4₁/acd net. Strong hydrogen bonding among the organic SDAs, water molecules, and Ge₁₀ clusters resulted in helical networks in SU-67.