Longitudinal positional ordering of n-alkane molecules in urea inclusion compounds
Acta Crystallographica Section B-Structural Science 56: 132-141
The profiles of diffuse layers, which are present in diffraction patterns of urea inclusion compounds, are interpretted 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.