DISORDER AND DIFFUSE SCATTERING OF CHANNEL TYPE INCLUSION COMPOUNDS WITH PERHYDROTRIPHENYLENE. O. König¹, H.B. Bürgi², T. Armbruster², J. Hulliger¹, Institute of Inorg., Analyt. and Physical Chemistry, University of Berne, Switzerland¹, Laboratorium of Chem. and Miner. Crystallography, University of Berne, Switzerland²

Intensive diffuse scattering is observed for a series of new crystalline inclusion compounds of racemic perhydrotriphenylene (PHTP) [1]. In these compounds stacks of PHTP form channels along the unique c axis hosting linearly shaped donor (D) - acceptor (A) substituted [[pi]]-systems as guests [2].

For such guests X-ray photographs show difffuse scattering concentrated in plans perpendicular to the channel axis. This is explained by an one dimensional translational order of guest molecules within each channel (c_guest) and a lack of translational order between different channels. The period c_guest almost always agrees with the assumption of close packing along the channels and, depending on the ratio c_host/c_guest both commensurate and incommensurate cocrystals have been found. For a few cases, satelite reflections superimposed onto the diffuse layers indicate some correlation between guest molecules in different channels.

Analysis of Bragg scattering of the commensurate system { 1-(4-Nitrophenyl)-piperazine} ^.{PHTP} ₅ revealed a centrosymmetric space group (Cmcm) for the host lattice and a polar space group Cmc2₁ for the guest molecules implying a parallel alignment of 1-(4Nitrophenyl)-piperazine dipoles in different channels. The mechanism responsible for parallel alignment of the dipole in different channels, which are 14 Å apart, is until now not understood.

[1] M. Farina, in Inclusion Compounds 2 (Eds.: J.L. Atwood, J.E.D. Davis, D.D. MacNicol), Academic Press, London 1984, 69-95;

[2] J. Hulliger, O. König, R. Hoss, Adv. Mater. 7 (1995), 719-721.