Host-guest complexation involving the cyclophanes

In 1955, cyclophane derivatives of type (261) (with n = 3 or 4) were described (Stetter Roos, 1955). After recrystallization from benzene or dioxan, these species crystallized as the 1 1 adducts of these solvents. Once such adducts are formed, it is difficult to remove the solvent and it was concluded that the solvent molecules are housed inside the cavities of the respective guests. In accord with this, the smaller ring system (261  

More recently, the water-soluble paracyclophane (263) was demonstrated to form crystalline complexes with a range of hydrophobic substrates under acid conditions (Odashima, Itai, Iitaka Koga, 1980). For example, with durene (264), a complex of stoichiometry [host.4HCl. durene.4H20] was obtained. The X-ray structure of this species indicates 

It should be noted that not all host-guest phane complexes are of the type just described. Indeed, a significant number of lattice inclusion complexes also occur. In these, the host molecules stack such that a channel running between hosts is formed. Guest molecules occupy this channel. As expected, such an arrangement is usually reflected by relatively poor host-guest selectivity. 

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