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A new borate polyanion in the structure of N 8 [B 12 O 20 (OH) 4 ]

1979; International Union of Crystallography; Volume: 35; Issue: 11 Linguagem: Inglês

10.1107/s0567740879009742

1600-8650

S. Menchetti, C. Sabelli,

Bone Tissue Engineering Materials

Na20.3B20 a. H~O is a new phase synthesized at 523 K under hydrothermal conditions. Crystal data are: a = 8.709 (3), b = 11.917 (5), c = 9.468 (3) ,/k, fl = 96.02 (2) °, space group P2t/c and Z = 4. The atomic positions, including those of the H atoms, were deter- mined by direct methods and difference Fourier syntheses, and refined by least-squares calculations to an R of 0.030 for 2077 reflexions measured on a computer-controlled automatic diffractometer. The basic structural unit is the isolated polyanion (B12020(OH)4 )8- with point symmetry i. The poly- anion, which is new in the crystal chemistry of borates, is built up by the linkage of three tetrahedra and three triangles, doubled by the symmetry centre. It can be described as a loop of six six-membered B-O rings. Of the three independent oxygens linked to only one triangular boron, only two exist as hydroxyl groups. Na-O polyhedra form a tight network by sharing corners, edges and faces. All O atoms linked to Na atoms belong at the same time to the B-O polyanions. The structural formula is Nas(B 12020(OH)4).