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

Abstract A new series of macrocyclic diamides with carboxyl, pyridyl and picolinate pendant arms have been synthesized and the stability constants of their complexes with Ni 2+ , Cu 2+ , Zn 2+ , Cd 2+ , Pb 2+ 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 (logβ ML  =  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 Cu 2+ and Zn 2+ complexes revealed the external coordination of the metal atom by amine N atoms of the macrocycle and heteroatoms of the pendant groups.