New halogen germanates of Sr and Ba

Crystals of four novel compounds, Sr3GeO4Cl2, Ba3GeO4Br2, Sr6Ge2O7Cl6, and Ba5GeO4Br6, were obtained through solid state sintering and flux growth. Single crystal X-ray diffraction revealed that Sr3GeO4Cl2 and Ba3GeO4Br2 are structurally related to Mg3SiO4(F,OH) (but not isostructural due to the significant difference in ionic radii). Application of the RHal 2 (R ​= ​Sr, Ba; Hal ​= ​Cl, Br) fluxes for the crystal growth yielded the Sr6Ge2O7Cl6 and Ba5GeO4Br6 phases with smaller Ge: Hal ratios. Presence of the additional Hal − anions accounts for the formation of 3D units built from Ba2+ and Br− in Ba5GeO4Br6, while in the other germanates the highest dimensionality of the R 2+ - Hal − units is 2.