Self-assembling resorcinarene capsules: solid and gas phase studies on encapsulation of small alkyl ammonium cations

The self-assembling process of unsubstituted resorcinarenes (1, 2 and 3) to dimeric capsules encapsulating small tetra-alkyl ammonium cations 4-7 has been studied in solid and gaseous states by X-ray crystallographic and mass spectrometric methods. Hydrogen bonding and cation-pi interaction as well as the proper encapsulation in the empty cavity of the capsule appear to be the most important interactions in the capsule formation process. Competitive mass spectrometric studies clearly indicated preference of the tetramethyl ammonium cation (4) over tetraethyl ammonium cation (6) and especially tetrabutyl ammonium cation (7). The crystal structures of altogether eight dimeric capsules of resorcinarenes 1-3 with cations 4 and 5 were determined. In the solid state, the alkyl chain length of the host affects the crystal packing significantly. However, ethyl resorcinarene (2) is the only host, which binds the spherical halide anion (Cl- or Br-) in between the lower rim alkyl chains.