THE STRUCTURE OF THE FRAMEWORK STRONTIUM ALUMINATE SR6[AL12O24].BI2O3WITH AN INCLUDED BI2O3 MOLECULE

We have determined the crystal structure of the aluminate Sr6[Al12O24] .Bi2O3 obtained as a side phase in the Bi-Ca-Sr-Cu-O system as a resul t of its interaction with the Al2O3 crucible material. The aluminate h as a trigonal unit cell with a = 17.720, c = 7.107 angstrom, V = 1933 angstrom3, space group R3BAR, Z = 3. Experimental data were obtained o n a RED-4 diffractometer (lambdaMoK(alpha), 509 F(hkl), R = 0.052, d(c alc) = 4.38 g/cm3). In the framework of AlO4 tetrahedra, we have isola ted a 12-atomic block of a new 3-6-3 type as a secondary building unit (SBU). The block consists of a corrugated sixfold ring and six triple rings. The blocks are stacked according to the rhombohedral law to fo rm elongated sixfold and eightfold rings. A distinctive feature of the structure is the presence of a trigonal-bipyramidal ''molecular'' Bi2 O3 group not observed before. Its structural genetic role in the forma tion of this framework compound of the clathrate type is considered. F or Sr aluminate, a corrected formula with a similar structure describe d in literature is proposed, namely, 6SrAl2O4.NaSr(OH)3, but not 6SrAl 2O4.1.5Sr(OH)2.