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H. Gerke, Hermann Gies

Studies on clathrasils. IV

Synthetic dodecasil 1 H, 34Si0₂ * 3 M^12´ * 2 M^12´ * 1 M²⁰, with M¹² and M^12´ = N₂ and M^2O = piperidine, is hexagonal with space group P6/mmm and a =13.783(4) and c =11.190(3) Å. Structure refinement with 658 independent reflexions led to a weighted R_w = 0.056. The clathrate compound has a silica host framework and organic guest molecules M within three different types of cages. It is the simplest member (1-layer polytype) of the polytypic series ofdodecasils. Corner sharing [Si0₄ ] tetrahedra form a 3-dimensionaI 4-connected net which is built up from hexagonal layers of face sharing pentagondodecahedra ([5¹²] cages), the fundamental cage of the dodecasil series. Connecting such layers in sequence AA two new types of cagelike voids arise, the [4³5⁶6³] cage and the [5¹²6⁸] cage. The guest molecules M¹², M^12´ and M²⁰, which must be present during synthesis, show up in difference Fourier syntheses. The entrapped molecules are oriented within the cages such that van der Waals contacts between guest molecules and host framework are optimized. The mean value of the Si-0 -Si angles (170.6°) is considerably higher and the mean value of Si-0 distances (1.565 Å) is considerably lower than corresponding angles and distances of silica polymorphs.

Zeitschrift für Kristallographie, Oldenbourg Wissenschaftsverlag

Print ISSN: 0044-2968
Volume: 166, 01/1984
Pages: 011 - 022

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