Complexation of planar, organic, five-membered cations with crown ethers

Abstract

Complexation of six aromatic, nitrogen-containing cations with various crown ethers has been studied using ¹H NMR, mass spectrometric and crystallographic methods. Hydrogen bonding appears to be the most important interaction in complexation, but minor effects such as π-stacking or cation–π interactions have also been observed. The stability constants of five different imidazolium perchlorate ·crown ether complexes and five other similar cation·DB18C6 complexes were determined by ¹H NMR titration in acetonitrile solution. The stability of these complexes in solution and in the gas phase is discussed. The crystal structures of seven complexes were determined in order to study complexation in the solid state. Four of these are imidazolium complexes with different crown ethers and three are complexes of dibenzo-18-crown-6 with similar planar cations.