Unusual Encapsulation of Two Anions in the Cavity of Neutral Macrocyclic Octalactam, Preliminary Communication

Abstract

A new neutral anion receptor – macrocyclic octalactam 2, possessing a large 36-membered ring, was synthesized, and its unusual property of encapsulation of two Cl− ions and two H2O molecules in the cavity was confirmed by X-ray crystallography (see Figure). The octalactam, consisting of four 2,6-dicarbamoylpyridine and four ethylene moieties, exhibits a symmetrical, fully expanded conformation in the complex [(Cl)2(2)(H2O)2]2− (obtained as 2⋅2 Bu4NCl⋅4 H2O⋅2 CH2Cl2). Inside the cavity, encapsulated species – two Cl− ions and two H2O molecules – are connected to each other by H-bonds. This kind of complex-in-complex system is formed by means of twenty intra-ring H-bonds and additionally four from the ‘outside' H2O molecules. Considering size and symmetry, it can be stated that the planar (H2O⋅Cl−)2 dimer fits well into the cavity of octalactam 2. The ligand has an optimal arrangement of binding sites to form H-bonds to every corner of the dimer.