Staircase Inclusion Compounds Formed by Tetrahalodiquinoline Hosts A. Noman M. M. Rahman, Roger Bishop,* Donald C. Craig, Christopher E. Marjo, and Marcia L. Scudder School of Chemical Sciences, The University of New South Wales, UNSW Sydney New South Wales 2052, Australia Received May 1, 2002 W This paper contains enhanced objects available on the Internet at http://pubs.acs.org/crystal. ABSTRACT: The tetrabromodiquinoline 2, and its tetraiodo counterpart 3, are members of the new tetrahalo aryl host family. They form lattice inclusion compounds when crystallized from many organic liquids, and the X-ray crystal structures of five such compounds are reported and analyzed in crystal engineering terms. Host molecules assemble into parallel staircases by means of aryl offset face-face and halogen-halogen interactions both within, and between, the staircases. The guests are situated in parallel interstitial channels. Variation of the type of included guest can result in significant changes to the construction and symmetry of the host staircase assemblies. Introduction Many well-known organic hosts (such as crown ethers, cyclodextrins, cryptands, and calixarenes) have a pre- formed receptor structure that can combine with a guest species to produce an inclusion compound. 1,2 The be- havior and properties of such molecules often may be predicted or modeled comparatively easily. This is no longer true, however, for lattice inclusion (clathrand) hosts (for example thiourea, tetraaryl porphyrins, and bile acids). For this alternative group of compounds, molecular inclusion occurs as a result of the interactions present between the many hosts and guests comprising their crystal lattice. Hence prediction, design, and crystal engineering development of new lattice inclusion hosts generally have been more difficult than for the former group of hosts. 3 Historically, chance discovery has uncovered many lattice inclusion hosts, and their subsequent systematic modification into new structures has also been produc- tive. Now our rapidly developing understanding of intermolecular forces, lattice packing, and supramo- lecular chemistry can be applied to such problems. 4-6 A significant proportion of known clathrand hosts incorporate hydrogen bonding functionality (especially the hydroxy group) as part of their structure. Hydrogen bonding is a relatively strong intermolecular attractive force that provides some degree of predictability in lattice inclusion host design. 7-11 In this paper, we describe the inclusion properties of a new type of lattice inclusion host 2, the structure of which does not usually hydrogen bond with either itself or guest molecules. Instead, combinations of different weak intermolecular attractions such as aryl offset face-face (OFF), aryl edge-face (EF), C-H‚‚‚halogen, nitrogen-halogen, and halogen-halogen interactions can be involved in the resulting inclusion structures. Results and Discussion Synthesis, Inclusion, and Crystallization. The preparations of the tetrabromo host 2, and its tetraiodo analogue 3, are illustrated in Scheme 1. We have reported earlier that Friedla ¨ nder condensation 12,13 of bicyclo[3.3.1]nonane-2,6-dione 14 with two equivalents of o-aminobenzaldehyde 15 affords the diquinoline adduct 1. 16 Quinoline is known to be preferentially bromi- nated, 17,18 or iodinated, 19 at its 5 and 8 positions if the halogenation is conducted in concentrated sulfuric acid in the presence of silver sulfate. These sites correspond to the 1, 4, 9, and 12 positions of the diquinoline molecule 1, and we found that bromination of this compound did indeed afford the 1,4,9,12-tetrabromo derivative 2 (46%). 20 A similar iodination experiment yielded the tetraiodide 3 in 55% yield. The tetrabromide 2 proved to be an excellent host for inclusion of many small molecules such as dichloro- methane, benzene, tetrahydrofuran, 1,1,2,2-tetrachlo- roethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane, toluene, and ethyl acetate. Furthermore, an allyl cya- nide-water mixture was also included by 2. Although solid inclusion compounds could be obtained by evapo- ration of solvent from solutions of 2, in all cases it proved exceptionally difficult to grow crystals of suitable quality for X-ray structural investigations. This proved to be even more difficult for the tetraiodide host 3, which includes guests such as toluene and chloroform. None- * To whom correspondence should be addressed. Fax: 61-2-9385- 6141. E-mail: r.bishop@unsw.edu.au. Scheme 1 CRYSTAL GROWTH & DESIGN 2002 VOL. 2, NO. 5 421 - 426 10.1021/cg020017o CCC: $22.00 © 2002 American Chemical Society Published on Web 08/03/2002