The new framework germanate (H3NC3H7) 5(H3O)[Ge18O36(OH)6] · 3H2 (tetragonal, 14cm, a = 24.9728-(6) Å, c -9.8957(2) Å, Z -4) has been synthesized by solvothermal methods and the crystal structure determined using single-crystal X-ray diffraction data. The framework of this novel material contains a three-dimensional intersecting channel system, the two largest channels of which are encompassed by large circular 16-rings and elliptical 14-rings. respectively. The material is synthesized in the presence of the relatively small structure-directing agent isopropylamine. (H3NC3H7)5(H3O)[Ge 18O36(OH)6] · 3H2 is only the second material to be constructed from the secondary building unit [Ge 9(O,OH)25] cluster, and the frameworks of these two materials are shown to differ only by the number of chains of [Ge 9(O,OH)25] clusters that are used to construct the respective frameworks. Thermal stability studies indicate that the framework of the material is stable with respect to loss of the extraframework water molecules but is unstable with respect to the removal of the extraframework charge-compensating cations. © 2007 American Chemical Society.