Out-cage metal ion coordination by novel benzoazacrown bisamides with carboxyl, pyridyl and picolinate pendant arms

A new series of macrocyclic diamides with carboxyl, pyridyl and picolinate pendant arms have been synthesized and the stability constants of their complexes with Ni2+, Cu2+, Zn2+, Cd2+, Pb2+ in water were determined. Complexes with a stoichiometry of 1 : 1 (M: L) were found for all ligands with the exception of 15-membered crown ethers with one pendant carboxyl or pyridine group. The ligand containing two picolinate backbone groups exhibits the highest values of the stability constants for all studied cations (logβML = 12.5–15.7). X-ray study of free ligands showed that the introduction of benzene and amide fragments into the macrocyclic moiety provides a flatten open structure of the ligand. The crystallographic analysis of Cu2+ and Zn2+ complexes revealed the external coordination of the metal atom by amine N atoms of the macrocycle and heteroatoms of the pendant groups.