Inclusion complexes of the bicyclic aryl-substituted sulfur-nitrogen compounds Ar-CN5S3 with fluorocarbon and hydrocarbon aromatics

Inclusion compounds with a stoichiometry of 2:1 were prepared from 7-Ar-1lambda(4),3lambda(4),5lambda(4)-trithia-2,4,6,8,9-pentaazabicyclo[3.3.1]nona-1(9),2,3,5,7-pentaenes Ar-CN5S3 and hexafluorobenzene (Ar = C6H5, 4-CH3C6H4, 4-C6H5C6H4 and 2,6-F2C6H3) and toluene (Ar = C6F5), by crystallization of the bicycles from the corresponding aromatics. Similar to the pure host compounds, the bicycles in the inclusion compounds form centrosymmetric dimers. The packing of the dimers in the pure host compounds is dominated by the interaction of the substituents at the aryl groups, and in the inclusion compounds by the interaction of the host and guest. The parallel-displaced arrangement of the aromatic rings of the host and guest is typical of non-covalent pi-stacking interactions of the arene-polyflurodrene type. The inability of benzene (in contrast to hexafluorobenzene) to form an inclusion compound with the title bicycle (Ar C6H5) indicates that inclusion is driven by pi-stacking interactions of the arene-polyfluoroarene type. Crystallization of the title bicycle (Ar = C6H5) from a 1:1 molar mixture of benzene and hexafluorobenzene gave the same inclusion compound as the crystallization from pure hexafluorobenzene. This can be considered as molecular recognition based on pi-stacking interactions. The compounds prepared provide the first example of aromatic units bearing extremely sterically demanding polyheteroatom bicyclic substituents involved in non-covalent arene-polyfluoroarene pi-stacking interactions. Attempts to prepare inclusion compounds with octafluoronaphthalene and decafluorobiphenyl, as well as co-crystals of para-tolyl- and pentafluorophenyl-substituted bicycles, failed. The origin of the 2:1 stoichiometry and the lack of inclusion in the case of C12H10 and C10F8 are discussed. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).