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

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.