SU-75: a disordered Ge10 germanate with pcu topology

Abstract

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 I42d (No. 122) with a = 18.145(3) Å and c = 41.701(9) Å. The three-dimensional (3D) framework is built from Ge(10)(O,OH)(28) (Ge(10)) 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 Ge(10) clusters (4Ge(10) unit). The chemical formula of SU-75 is |(H(2)SDA)(2)(H(2)O)(n)|[Ge(10)O(21)(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 Ge(10) clusters and to illustrate the disorder. This is also used to compare the structure of SU-75 with those of related Ge(10) germanates.