BaY2Si3O10: A new flux-grown trisilicate.

BaY2Si3O10, barium diyttrium trisilicate, is a new silicate grown from a molybdate-based flux. The structure is based on zigzag chains, parallel to [010], of edge-sharing distorted YO6 octahedra, linked by horseshoe-shaped trisilicate groups and Ba atoms in irregular eight-coordination. The layered character of the structure is caused by a succession of zigzag chains and trisilicate groups in planes parallel to (-101). The Ba atoms occupy narrow channels extending parallel to [100]. The mean Y-O, Si-O and Ba-O bond lengths are 2.268, 1.626 and 1.633, and 2.872 A, respectively. The two symmetry-equivalent terminal SiO4 tetrahedra in the Si3O10 unit adopt an eclipsed conformation with respect to the central SiO4 tetrahedron; the Si-O-Si and Si-Si-Si angles are 136.35 (9) and 96.12 (4) degrees, respectively. One Ba, one Si and two O atoms are located on mirror planes; all remaining atoms are in general positions. The geometry of isolated trisilicate groups in inorganic compounds is briefly discussed.