Complexation of enantiomerically pure tetraalkylammonium cations by ethyl resorcinarene

Molecular recognition via weak interactions of three enantiopure tetraalkylammonium cations 2–4 by ethyl resorcinarene 1 was studied in the solid state using single-crystal X-ray diffraction, in solution by proton nuclear magnetic resonance spectroscopy (1H NMR) titration and in the gas phase using electrospray ionisation mass spectrometry. The 1H NMR titration studies reveal the association constants for the 1:1 complexes to vary according to the size and electronic properties of the alkyl groups of the guest cations. In the solid state, the resorcinarene is deprotonated and the X-ray structure confirms the 1:1 complex 2+@1− to be held together by multiple cation…π and C–H…π interactions. The 1:1 inclusion [2–4@1]+ complexes were observed as the major species in the gas phase.