Crystal Engineering Involving C−H···N Weak Hydrogen Bonds: Penannular Enclosure of Organic Guests by a Diquinoline Host

Abstract

The preparation and properties of the racemic lattice inclusion host 6α,13α-dibromo-5bα,6,12bα,13-tetrahydropentaleno[1,2-b:4,5-b′]diquinoline (8) are described. Strong hydrogen bonding interactions are not possible for this versatile host compound. Instead, weaker interactions (such as aryl offset face-face, aryl edge-face, halogen-halogen, halogen-π, and C−H···N synthons) compete against each other to generate the inclusion structure of lowest energy. The guests are contained within molecular pens formed by two hosts enclosing each guest. These host molecules are not directly linked at the corners of the pen, but rather assemble with their neighbours into layers of pens by means of aryl offset face-face interactions. The C−H···N weak hydrogen bond plays a dominant role in these structures by linking adjacent layers edge-edge through two distinct types of double motifs. One is the previously recognised aryl C−H···N dimer, while the other is a new bifurcated Ar−H···N···H−CBr−Ar interaction. The X-ray structures of nine inclusion compounds formed by 8 are reported. Seven of these in space group P21/c have isostructural host lattices where the layers of pens are stacked to produce guest channels. Several different guest arrangements are observed. In contrast, (8)2·(CH3CCl3) in space group C2/c and (8)2·(CF3C6H5) in P212121 have the pen layers stacked so as to enclose their guests in cages. The structure of the nonbrominated precursor 7, which undergoes self-resolution on crystallisation, is also described in crystal engineering terms. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)