Synthesis and crystal structure of new layered BaNaSc(BO sub(3)) sub(2) and BaNaY(BO sub(3)) sub(2) orthoborates

Crystals of two new layered BaNaSc(BO sub(3)) sub(2) ( I) and BaNaY(BO sub(3)) sub(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) Aa, and c=34.5919(11) and 35.8303(19) Aa for I and , respectively, Z=6. The distinctive feature of the structure is the close-packed composite anion-cation (Ba,Na)(BO sub(3)) layers. The layers are combined into the base building packages of two types: {M super(3+)[Ba super(2+)(BO sub(3)) super(3-)] sub(2)} super(+) and {M super(3+)[Na super(+)(BO sub(3)) super(3-)] sub(2)} super(-), 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.