Halogen-Bonded Supramolecular Capsules in the Solid State, in Solution, and in the Gas Phase

Supramolecular capsules were assembled by neutral halogen bonding (XB) and studied in the solid state, in solution, and in the gas phase. The geometry of the highly organized capsules is shown by an X-ray crystal structure which features the assembly of two XB hemispheres, geometrically rigidified by H-bonding to eight MeOH molecules and encapsulation of two benzene guests. To enhance capsular association strength, tuning the XB donor is more efficient than tuning the XB acceptor, due to desolvation penalties in protic solvents, as shown for a tetraquinuclidine XB acceptor hemisphere. With a tetra(iodoethynyl) XB donor and a tetralutidine XB acceptor, the association in deuterated benzene/acetone/methanol 70:30:1 at 283 K reaches K-a = (2.11 +/- 0.39) X 10(5)m(-1) (Delta G = -6.9 perpendicular to 0.1 kcal mol(-1)). The stability of the XB capsules in the gas phase was confirmed by electrospray ionization mass spectrometry (ESI-MS). A new guest binding site was uncovered within the elongated iodoethynyl capsule.