SR4RU2O9 - A STRUCTURAL MODEL RESULTING FROM THE STACKING OF [SR3O9] AND [SR3O6] MIXED LAYERS - STRUCTURAL RELATIONSHIPS TO RELATED PEROVSKITE-TYPE STRUCTURES

A novel compound, Sr4Ru2O9, has been prepared and its crystal structur e has been determined on single crystal X-ray. It was found to crystal lize in the space group P (6) over bar 2c, a = 9.642(2)Angstrom, c = 8 .104(2)Angstrom, Z = 3. The reliability factors are R1 = 0.039 and wR2 = 0.066 for 553 unique structure factors and 31 parameters. Perpendic ular to the c asis, the structure is built up from the periodic stacki ng of one close packing [Sr3O9] layer similar to those of the hexagona l perovskites and three [Sr3O6] layers. These last ones result from th e [Sr3O9] layers by removing three oxygens in an ordered way. The stac king of these mixed layers is of her;agonal type and then columns para llel to the c asis are formed which are separated by the strontium ato ms. The columns consist of octahedra and trigonal prisms sharing faces . The ruthenium atoms occupy only the octahedra and then constitute [R u2O9] isolated dimers. The structural relationships to the hexagonal p erovskites and related compounds are discussed.