Cryptates XXIV : Structure and stability of mononuclear and binuclear cation inclusion complexes of cylindrical macrotricyclic ligands

The cylindrical macrotricyclic ligands 1–3 yield inclusion complexes, [3]‐cryptates, with various metal cations. NMR. studies indicate the successive formation of a mononuclear and a binuclear complex. The former is probably unsymmetrical undergoing fast intramolecular cation exchange; the latter is symmetrical, with a cation located on each macrocyclic subunit of the macrotricyclic system. A heteronuclear (Ag²⁺, Pb²⁺) complex has been observed. The stability constants of the mononuclear and binuclear alkali and alkaline‐earth cation complexes of ligands 1–3 have been determined by potentiometric methods. The stabilities are comparable to those of the complexes of the isolated macrocyclic subunit 5b. The binuclear complexes are almost as stable as the mononuclear one even in highly charged species like for instance the complex of ligand 2 with two barium cations. Cylindrical macrotricyclic ligands are topologically well suited for the designed positioning of two metal cations in a binuclear inclusion complex. Copyright © 1977 Verlag GmbH & Co. KGaA, Weinheim