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

Abstract

The RbSbGe3O9 compound, grown by the high-temperature solution technique from the Rb2Mo4O13 flux, crystallizes in the trigonal non-centrosymmetric space group P31c (no. 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 RbSbGe3O9 network is built with three-membered units [Ge3O9]6- of regular germanate tetrahedra involving three crystallographically independent Ge atoms. The Ge3O3 central rings located in the ab plane deviate only slightly from the planarity. Antimony SbV is octahedrally coordinated by oxygen, and rubidium (Rb+), which is surrounded by six oxygen atoms, is located in the channels of the 3-D network. The structure of RbSbGe3O9 containing both isolated SbO6 octahedra and Ge3O9 cyclic units is comparable but not isostructural to the benitoite type. The almost flat character of the Ge3O3 rings is also attested by the vibrational study at room temperature via non-polarized infrared and Raman spectroscopy.