Synthesis, Structure, and Characterization of Keggin-Type Germanate

Abstract

A novel Keggin-type germanate, (NH4)9[Ge7O14F3]3·1.75H2O (I), is hydrothermally synthesized and structurally characterized by X-ray single-crystal diffraction, elemental analysis, XRD, and TG. (I) is tetragonal system with space group I4/mmm and unit cell: a=28.280 (4) Å, c=24.881(5) Å, V=19899(6) Å3, Dc=1.632 g/cm3, μ(Mo Kα)=6.309 mm−1, Z=2 , R1=0.1141 for 2576 reflections with Fo>2(Fo). Ge7O14F3 entry is defined as the cluster including one octahedron, two edge-sharing triganol bipyramids, and four tetrahedra. Every Ge7O14F3 entry links adjacent four Ge7O14F3 entries by four tetrahedra. Twelve Ge7O14F3 entries construct a cage with all octahedra of Ge7O14F3 pointing inside, which can be simplified into Keggin-type cage through Ge7O14F3 as the node. The solvent experiment proves that (I) is stable in the water and sensitive to base and acid. The result of XRD shows that the structural water of (I) is easily lost to drop the crystalline. The thermal study indicates that the Keggin-type cage of (I) begins to partly collapse at 200°C and finally changes into GeO2.