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Figure 7
Comparison of the [512]- and [51264]-type cages at (a) T = 100 K (A2/n), and (b) 293 K ([Fd{\overline 3}m]). Small red spheres represent the O atoms, and the large blue spheres are the Si atoms. Several Si—O—Si angles bend significantly in the LT form (100 K) in comparison with that at RT (293 K). (c) The four crystallographically different [512]-type cages (100 K, A2/n), inter­connected by sharing common five-membered ring units; the symmetry-released C1 atoms (labeled C1a, C1b, C1c, C1d) are located in the cage centers. All atoms are shown as 50% probability ellipsoids recalculated from the corresponding Uij values. As a result of the strong bending of the Si—O—Si bond angles, the individual cages are subject to significant distortions at LT and the deviation from the (average) [Fd{\overline 3}m] symmetry is evident.

IUCrJ
Volume 5| Part 5| September 2018| Pages 595-607
ISSN: 2052-2525
https://doi.org/10.1107/S2052252518009107