Complexation between pillar[5]arenes and a secondary ammonium salt.

We demonstrate that n-octylethyl ammonium hexafluorophosphate (G) can thread through the cavity of 1,4-dimethoxypillar[5]arene to form a [2]pseudorotaxane with a binding constant of 1.09 (±0.31) × 10(3) M(-1) in chloroform. The formation of this threaded structure has been confirmed by proton NMR spectroscopy, electrospray ionization mass spectrometry, and X-ray single crystal analysis. The complexation between 1,4-dimethoxypillar[5]arene and G in chloroform can be switched off by adding Cl(-). For comparison, the complexation between 1,4-bis(n-propoxy)pillar[5]arene and G has also been investigated.