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 (Ka) of up to 5370 M−1 (ΔG283 K=−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 Ka=9.0 108 M−2 (ΔG283 K=−11.6 kcal mol−1). Time for halogens: Self‐assembly of supramolecular capsules solely by halogen bonding (XB) is realized on the platform of resorcin[4]arene cavitands. The halogenated donor hemisphere binds in a 180° fashion through tetradentate XB to the acceptor hemisphere for capsule formation in solution. Guest inclusion inside the XB capsule is demonstrated and quantified.