Longitudinal positional ordering of n-alkane molecules in urea inclusion compounds
The profiles of diffuse layers, which are present in diffraction patterns of urea inclusion compounds, are interpreted quantitatively by a longitudinal positional paracrystalline order of the alkane guest molecules within the channels of the urea-host framework structure, in agreement with the expected behaviour of a one-dimensional system. With decreasing temperature there is a gradual transition into long-range order behaviour. This ordering process remains unaffected by structural changes related to lateral correlations within and between both host and guest substructures, including a structural phase transformation. The differing behaviour of a mixed system (pentadecane/hexadecane) with average period almost commensurate with the urea host lattice is explained by the superposition of main and satellite layers. The distribution of both molecules within each tunnel is random.
Weber
T
Institut fur Kristallographie und Angewandte Mineralogie, Ludwig-Maximilians-Universitat Munchen, Germany. thomas.weber@krist.unibe.ch
Boysen
H
Frey
F