Halogen-Bonded Supramolecular Capsules in the Solid State, in Solution, and in the Gas Phase
O. Dumele, B. Schreib, U. Warzok, N. Trapp, C.A. Schalley, F. Diederich – 2017
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 capsule is evidenced 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. Tuning the XB donor is more efficient for enhancing capsular association strength 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 Ka = (2.11±0.39)×105 M–1 (deltaG = –6.9±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.