J. Dunitz, M. Dobler, P. Seiler
Nov 15, 1974
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Journal
Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry
Abstract
The results of crystal structure analyses of 1,4,7,10,13,16-hexaoxacyclooctadecane (CH2CH20)6 and its complexes with NaNCS, KNCS, RbNCS, CsNCS [and Ca(NCS)2] are discussed. In the K*, Rb*, Cs* and Ca 2+ complexes the unsubstituted hexaether adopts a conformation with virtual Ds~ symmetry although the larger Rb + and Cs + ions are displaced by more than 1 ,~, from the mean plane of the ligand. In the Na* complex, the ring is strongly distorted from its symmetrical conformation to accommodate the smaller cation. The uncomplexed hexaether has a centrosymmetric conformation containing three different types of monomeric subunit. The shortening of the C-C bonds found in these and related complexes is discussed and judged to be mainly an artificial effect arising from inadequate treatment of curvilinear vibrations.