Hydroflux syntheses and crystal structures of hydrogarnets Ba${}_3$[RE(OH)${}_6$]${}_2$ (RE = Sc, Y, Ho–Lu)

Colorless crystals of the barium rare earth hydrogarnets Ba${}_3$[RE(OH)${}_6$]${}_2$ (RE = Sc, Y, Ho–Lu) were synthesized under hydroflux conditions with KOH at about T = 200 °C starting from the respective RE${}_2$O${}_3$ and Ba(NO${}_3$)${}_2$. Single-crystal X-ray diffraction analysis on these distorted rhombic dodecahedra revealed the cubic space group Ia$\overline{3}$d (no. 230). The crystal structures of the hydrogarnets Ba${}_3$[RE(OH)${}_6$]${}_2$ are discussed and compared with those of other hydrogarnets. The occurrence of additional reflections, which do not fulfill the reflection conditions of Ia3d, is analyzed and described by Renninger or λ/2 effects. A correlation is established between the space group adopted by a hydrogarnet and characteristic interatomic distances. In addition, single-crystal structure data of the strontium indium hydrogarnet Sr${}_3$[In(OH)${}_6$]${}_2$ are provided.