Résumé
We report on the preparation and the X-ray crystal structure of colorless KSbGe 3 O 9 , its vibrational properties (Raman and infrared studies), and density functional theory (DFT) calculations. KSbGe 3 O 9 , grown by the hightemperature flux method from K 2 Mo 4 O 13 flux, is thermally stable at least up to 1200 C and is isostructural to the benitoite BaTiSi 3 O 9 (space group P6c2 (n o. 188)). The hexagonal unit cell contains two formula units and the structure was refined to R1 ¼ 0.0324 from single-crystal X-ray diffraction data. KSbGe 3 O 9 is characterized with only one crystallographically independent Ge atom involved in three-member units [Ge 3 O 9 ] 6of regular germanate tetrahedra. The K þ ions are located in channels and, like Sb V , are octahedrally surrounded by oxygen atoms. The KSbGe 3 O 9 local structure and the planarity of Ge 3 O 3 rings are also studied by a room-temperature vibrational investigation using non-polarized infrared and Raman spectroscopy. Both the infrared and Raman phonon modes have been assigned from the agreement observed between our experimental data and the corresponding DFT ones. In particular, two E' (TO) modes (both IR and Raman active) characterize the planarity of the Ge 3 O 3 ring in the ab plane.