Single-crystal growth, structure, and optical properties of a new non-centrosymmetric germanate, RbSbGe3O9

Abstract : The RbSbGe 3 O 9 compound, grown by the high-temperature solution technique from the Rb 2 Mo 4 O 13 flux, crystallizes in the trigonal non-centrosymmetric space group P31c (n o. 159). The structure was solved and refined from single-crystal X-ray diffraction data recorded at ambient temperature. The unit cell contains six formula units. The three-dimensional RbSbGe 3 O 9 network is built with three-membered units [Ge 3 O 9 ] 6-of regular ger-manate tetrahedra involving three crystallographically independent Ge atoms. The Ge 3 O 3 central rings located in the ab plane deviate only slightly from the planarity. Antimony Sb V is octahedrally coordinated by oxygen, and rubidium (Rb þ), which is surrounded by six oxygen atoms, is located in the channels of the 3-D network. The structure of RbSbGe 3 O 9 containing both isolated SbO 6 octahedra and Ge 3 O 9 cyclic units is comparable but not isostructural to the benitoite type. The almost flat character of the Ge 3 O 3 rings is also attested by the vibrational study at room temperature via non-polarized infrared and Raman spectroscopy.