Halogen Bonding Molecular Capsules

Molecular capsules based solely on the interaction of halogen bonding (XB) are presented along with their host-guest binding properties in solution. The first example of a well-defined four-point XB supramolecular system is realized by decorating resorcin[4]arene cavitands with polarized halogen atoms for dimerization with tetra(4-pyridyl)resorcin-[4]arene cavitands. NMR binding data for the F, Cl, Br, and I cavitands as the XB donor show association constants (K-a) of up to 5370 m(-1) (Delta G(283K) = -4.85 kcal mol(-1), for I), even in XB-competitive solvent, such as deuterated benzene/acetone/methanol (70:30:1) at 283 K, where comparable monodentate model systems show no association. The XB capsular geometry is evidenced by two-dimensional HOESY NMR, and the thermodynamic profile shows that capsule formation is enthalpically driven. Either 1,4-dioxane or 1,4-dithiane are encapsulated within each of the two separate cavities within the XB capsule, with of up to K-a = 9.0 10(8) m(-2) (Delta G(283K) = -11.6 kcal mol(-1)).