Crystal Engineering Involving C−H···N Weak Hydrogen Bonds: A Diquinoxaline Lattice Inclusion Host with a Preference for Polychlorocarbon Guests

Abstract

The di(1,8-naphthryridine) 7 and diquinoxaline 12 derivatives were synthesised as potential new lattice inclusion hosts where strong hydrogen bonding interactions would be absent. A number of potential supramolecular synthons (such as aryl face-face, aryl edge-face, halogen-halogen, C−H···N, nitrogen-halogen) were expected to be accessible, with competing combinations of these weak attractions providing the best (but probably different) type of host-guest structure in each case. While the former compound turned out to be unstable, the latter proved to be a versatile host which preferred to trap small polychloroalkane guests. The X-ray structures of 12·(chloroform)2, (12)2·(tetrahydrofuran), and (12)2·(1,1,2,2-tetrachloroethane) are reported and shown to have different lattice packing where the guests occupy layers, parallel tubes, and molecular boxes, respectively. The detailed interplay of the above synthons in forming these structures is described in crystal engineering terms. Most significantly, the C−H···N weak hydrogen bond plays a major role in all three inclusion structures. Both single linear and double cyclic interactions are involved in molecular edge-edge assembly of the host 12. Several new types of double cyclic interactions were discovered revealing that the C−H···N interaction is a key synthon for crystal engineering involving nitrogen heteroaromatic compounds.