Characterization of intermolecular interactions in a disordered solid via a one-dimensional Patterson synthesis

We report the application of a one-dimensional Patterson analysis of diffuse X-ray scattering from the 1,8-diiodooctane/urea inclusion compound to obtain information on the intermolecular interaction between the iodine end groups of adjacent 1,8-diiodooctane guest molecules within the urea tunnel host structure in this inclusion compound. One aspect of the X-ray scattering from the guest component in this incommensurate inclusion compound comprises diffuse sheets perpendicular to the host tunnel axis, and we consider measurements of the intensity, I(l(g)), obtained from one-dimensional scans perpendicular to the diffuse sheets in reciprocal space (each diffuse sheet is specified by integer l(g)). The one-dimensional Patterson map constructed from I(l(g)) has a dominant peak at ca. 3.94 Angstrom, which is interpreted as the projection, on to the tunnel axis, of the intermolecular I...I distance. This value of D-z(I...I) is shown to be consistent with a model in which the iodine end groups are in van der Waals contact with the I --> I vector lying essentially parallel to the tunnel axis. We emphasize that this well-defined structural information has been obtained despite the substantial disorder in this system.