Acta Crystallographica Section C

Crystal Structure Communications

Volume 59, Part 10 (October 2003)

Acta Cryst. (2003). C59, i103-i106    [doi:10.1107/S0108270103018869]

-Y₂Si₂O₇, a new thortveitite-type compound, determined at 100 and 280  K

G. J. Redhammer and G. Roth

Abstract: A new form of Y₂Si₂O₇ (diyttrium heptaoxodisilicate) has been synthesized which is isotypic with thortveitite, Sc₂Si₂O₇, and crystallizes in the centrosymmetric space group C2/m, both at 100 and 280  K. The Y³⁺ cation occupies a distorted octahedral site, with Y-O bond lengths in the range 2.239  (2)-2.309  (2)  Å. The SiO₄ tetrahedron is remarkably regular, with Si-O bond lengths in the range 1.619  (2)-1.630  (2)  Å. The bridging O atom of the Si₂O₇ pyrosilicate group shows a large anisotropic displacement perpendicular to the Si-O bond. Changes in lattice and structural parameters upon cooling are small with, however, a distinct decrease of the anisotropic displacement of the briding O atom. Structure solution and refinement in the non-centrosymmetric space group C2 are possible but do not yield a significantly different structure model. The Si-O-Si bond angle of the isolated Si₂O₇ groups is 179.2  (1)° at 280  K in C2 and 180° per symmetry in C2/m. The C2/m structure model is favoured.

Formula: -Y₂Si₂O₇

Online 30 September 2003

	Structure factor file (CIF format) (25.7 kbytes) Contains datablock 280K
	Structure factor file (CIF format) (25.6 kbytes) Contains datablock 100K

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