Hydrothermal Synthesis and Structural Characterization of a New Organically Templated Germanate, Ge10O21(OH)·N4C6H21

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Abstract
A new open-framework germanium oxide Ge10O21(OH)·N4C6H21 has been hydrothermally synthesized at 180 °C for 6 days by using the tris(2-aminoethyl)amine (tren) molecule as a structure-directing agent. This compound was characterized by means of single-crystal X-ray diffraction and FTIR. It crystallizes in the noncentric monoclinic system Cm (a = 14.0495(2) Å, b = 12.8058(3) Å, c = 9.2637(2) Å, β = 128.406(1)°, Z = 4). Its three-dimensional framework is built up from GeO4 and GeO3(OH) tetrahedra connected by vertexes to GeO5 trigonal bipyramids and GeO6 octahedra. A pseudo-cubic building unit (“4-3” subunit) consists of four GeO4 tetrahedra, two GeO5 trigonal bipyramids, and one GeO6 octahedron (Ge7). In the “4-3” block, the GeO5 trigonal bipyramids share a common edge. This Ge7 entity is linked to three tetrahedral units GeO3X (X = O, OH), and this forms an original decameric building unit Ge10O21(OH) which is new in the germanates crystal chemistry. It results in a relatively dense open framework composed of pear-shape cavities (7862524432) encapsulating the triprotonated tren molecule. The inorganic network contains small pores delimited by 7-ring channels running along [001].