Structural complexity of a polar perhydrotriphenylene inclusion compound brought to light by synchrotron radiation.
The complex diffraction pattern of the heavily disordered co-crystals of perhydrotriphenylene and 1-(4-nitrophenyl)piperazine (5C(18)H(30) x C(10)H(13)N(3)O(2)) has been investigated with synchrotron radiation and an area detector. Five (almost) complete, three-dimensional data sets have been obtained from the tips and the centre of a needle-like crystal at room temperature and 120 K. They revealed a rich variety of features including one,- two- and three-dimensional diffuse scattering, as well as incommensurate satellites. At the centre and one tip of the crystal the symmetry appears to be orthorhombic, whereas at the other tip the symmetry of the satellites and of some of the diffuse scattering is clearly monoclinic, indicating that the crystal is not homogeneous. Most of the scattering could be assigned to R/S occupational disorder of the chiral host molecules, to positional disorder of the guest molecules or to local distortions of the average structure. Assignments are based on the disorder deduced from the average structure and the molecular form factors of host and guest molecules which show characteristic patterns in reciprocal space. Two smaller, orthorhombic twin fragments and an additional phase with hexagonal symmetry have also been found.
Weber
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Laboratory of Crystallography, Swiss Federal Institute of Technology Zürich, ETH Zentrum, Sonneggstrasse 5, CH-8092 Zürich, Switzerland. weber@kristall.erdw.ethz.ch
Estermann
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Bürgi
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