A disordered open-framework germanate, denoted as SU-75, was synthesized under hydrothermal conditions using diethylenetriamine (dien) or alternatively 1,4-diaminobutane (dab) as the structure directing agent (SDA). SU-75 crystallizes in a tetragonal space group I2d (No. 122) with a = 18.145(3) Å and c = 41.701(9) Å. The three-dimensional (3D) framework is built from Ge₁₀(O,OH)₂₈ (Ge₁₀) clusters that are connected following the pcu (primitive cubic) net topology. SU-75 has 10-, 11- and 12-ring channels along the a- and b-axes and channels with alternating 8-, 10-, 12-, 10-ring openings along the c-axis. The framework exhibits a serious disorder, resulted from two possible connectivities between the units of four Ge₁₀ clusters (4Ge₁₀ unit). The chemical formula of SU-75 is |(H₂SDA)₂(H₂O)_n|[Ge₁₀O₂₁(OH)₂] (SDA = dien or dab, n = 5–6), determined by combining single crystal synchrotron X-ray diffraction, thermogravimetric analysis (TGA) and CHN elemental analysis. A superoctahedron is introduced to simplify the description of the connectivity of the Ge₁₀ clusters and to illustrate the disorder. This is also used to compare the structure of SU-75 with those of related Ge₁₀ germanates.