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The crystal structure of silica sodalite, including possible locations for encapsulated ethylene glycol, was determined at room temperature by using a combined single-crystal X-ray and powder neutron diffraction analysis. Unit cell composition: Siij024-2C2H4(0H)2, , = 845, cubic, Im3m, a = 8.830 (1) Á (X-ray), a = 8.8273 (1) Á (neutron). These refinements reveal that the correct space group for silica sodalite is Im3m (rather than /43m) and, therefore, that the sodalite framework is fully expanded. At room temperature, each sodalite cage contains one ethylene glycol molecule which has a range of geometrical positions. Intramolecular distances for the ethylene glycol molecule are (X-ray) C-C 1.78 (4), C-0 1.30 (6) Á, (neutron) C-C 1.70 (3), C-O 1.25 (3) Á. The shortest distances (3.4 Á) between oxygens of the framework and molecule are consistent with weak hydrogen bonding. From the neutron diffraction data it was found that a sluggish phase change from cubic to lower symmetry occurs upon cooling below 200 K. At 10 K, silica sodalite appears to be monoclinic with approximate cell parameters a = 12.250 (8) Á, b = 12.471 (8) Á, c = 8.512 (6) Á, ß = 91.37 (6)°, based on an indexing of 12 peaks, but the precise symmetry is as yet unknown.

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Replacement of each 4-ring in a stack of congruent 2

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