| Abstract: | 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 result of its interaction with theAl2O3 crucible material. The aluminate has a trigonal unit cell with a=17.720, c=7.107 Å, V=1933 Å3, space group R?3, Z=3. Experimental data were obtained on a RED-4 diffractometer (λMoKα, 509 Fhkl, R=0.052, dcalc=4.38 g/cm3). In the framework of AlO4 tetrahedra, we have isolated 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 form elongated sixfold and eightfold rings. A distinctive feature of the structure is the presence of a trigonal-bipyramidal “molecular” Bi2O3 group not observed before. Its structural genetic role in the formation of this framework compound of the clathrate type is considered. For Sr aluminate, a corrected formula with a similar structure described in literature is proposed, namely, 6SrAl2O4·NaSr(OH)3, but not 6SrAl2O4·1.5Sr(OH)2. |
