Stereoisomerism of a wheel-axle shaped D.D.Host in supramolecular entities

Two types of supramolecular stereoisomers formed from a wheel - and - axle shaped host molecular 1, 1,6,6 - tetraphenylhexa - 2,4 - diyne - 1,6 - diol (1) and isopsoralen (2) or anethole (3) were assembled with the host/guest molar ratio being 1:2 and 2,: 1, respectively. The single crystal structur es of the free host and its two inclusion compounds were determined by X - ray diffraction analysis. The results show that in the crystal with host/gu est molar ratio being 1:2, the host bound to isopsoralen (2) by hydrogen bo nd adopts in antiperiplanar conformation, while in the 2:1 crystal, the hos t is in a gauche conformation due to the hydrogen bonding within the hosts. The observed modes of crystallization and molecular conformation of the ho st (1) were found to be primarily dependent on the nature of the guest envi ronment. An antiperiplanar conformation of the host (1) is formed in the gu est environment with good H - bond donors, while a gauche conformation is f avored in a relatively poor H - bond donor guest. The regularity of the cha nges in the dihedral angles of phenyl groups, the angles between the groups attached to C(1) and C(6) as well as the energy of the host compound in th e three crystals are also presented.