Abstract
A three-dimensional single crystal x-ray analysis of (CH3CH2)2NH·8⅔H2O has been carried out. The crystals are orthorhombic, with a=13.44 Å, b=11.77 Å, c=27.91 Å, and space group Pbcn. The compound is a clathrate hydrate, and the most notable feature of the water framework is a novel polyhedral cage, the 18-hedron (octakaidecahedron), which has twelve pentagonal and six hexagonal faces. The 18-hedra form a two-dimensional network by sharing faces. The networks are then linked together by additional water molecules in a manner which gives rise to additional ``irregular'' cages having quadrilateral, pentagonal, and hexagonal faces. Diethylamine molecules are enclosed in two types of cages and in both the amine groups are hydrogen bonded to the water lattice. In the case of the 18-hedra, this bonding somewhat distorts the cage from its ``ideal'' D3d shape. In marked contrast to previous clathrate structures involving polyhedra with pentagonal and hexagonal faces, where the dodecahedron could be considered to be the basic structural unit, the pentagonal dodecahedron does not appear in this structure.
Published Version
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