Synthesis and structure of (Me3N)6[Ge32O64]•(H2O)4.5, a thermally stable novel zeotype with 3D interconnected 12-ring channels

A compound with a novel zeotype topology, (Me3N)(6)[Ge32O64]. (H2O)(4.5) (Me3N = trimethylamine), was prepared from an aqueous solution containing germanium dioxide, pyridine, hydrofluoric acid and Dabco (Dabco = 1,4-diazabicyclo-[2,2,2]-octane) as a template. Small needle-shaped crystals were obtained. The crystals were studied by scanning electron microscopy, X-ray powder diffraction and thermogravimetric analysis. The structure was determined by single crystal X-ray diffraction to be tetragonal, space group I4(1)/amd, a = 25.990(3) Angstrom and c = 27.271(3) Angstrom, and Z = 8, V = 18420.88(391) Angstrom (3), R = 0.0604 for reflections with I > 2 sigma (1) and wR = 0.1696. The three-dimensional framework structure is built up by GeO4 tetrahedra, connected in such way that they form intersecting 12-ring channels along all three crystallographic axes. This is the first germanate zeotype with large intersecting channels. The free diameters of the apertures of the channels are 5.8 by 6.0 Angstrom along both the a- and the b-axes and 7.4 Angstrom along the c-axis. The porous structure is stable at temperatures sufficient for removing the organic template. (C) 2000 Elsevier Science B.V. All rights reserved.