Synthesis and crystal structure of new layered BaNaSc(BO_3)_2 and BaNaY(BO_3)_2 orthoborates

摘要

Crystals of two new layered BaNaSc(BO_3)_2 (I) and BaNaY(BO_3)_2 (II) orthoborates are grown from the melt-solution by the spontaneous crystallization onto the platinum loop. Single crystal X-ray analysis showed that the compounds are isostructural with the space group R3-, a=5.23944(12) and 5.3338(2) ?, and c=34.5919(11) and 35.8303(19) ? for I and II, respectively, Z=6. The distinctive feature of the structure is the close-packed composite anion-cation (Ba,Na)(BO_3) layers. The layers are combined into the base building packages of two types: {M~(3+)[Ba~(2+)(BO_3)~(3-)]_2}~+ and {M~(3+)[Na~+(BO_3)~(3-)]_2}~-, where M is Sc or Y. Neutral-charge two-package (four-layer) blocks are stacked by the rhombohedral principle into twelve layers of the cubic packing.