Cu(II) and Zn(II) complexes of new 12- and 13-membered dioxopolyazacycloalkanes with pendant amide groups

Abstract

The acid groups of the pendant arms of the ligands macrocyclic dioxotetraazacycloalkanediacetic acid, of 12- and 13-membered, were modified by amide groups. The modification was carried out using amidation reactions in a microwave reactor with the amines: N-butylamine, N-hexylamine, and phenylethylamine in presence of diisopropylcarbodiimide (DIC) and N-hydroxybenzotriazole (HOBt). Amidation of the pendant arms of the macrocyclic ligands increases the coordination sites of the molecules and decreases basicity the amino nitrogen atoms. Their Cu2+ chelates were characterized by electronic absorption spectra and their Zn2+ chelates were characterized by 1H NMR spectra in solution. Electronic spectra show that all the Cu2+ complexes derivatives from the ligands of 12-membered, have similar structures in acid and alkaline medium, but the complexes derived from the ligands of 13-members show a different geometry: octahedral geometry in acid medium and in a neutral or alkaline environment have a square planar structure, where the two nitrogen atoms of deprotonated amide and two amine nitrogen atoms are coordinated to the central metal ion. Coordination studies by 1H NMR of all ligands to zinc, indicating that the metal is coordinated with the donor atoms of the macrocyclic rings, besides the oxygen atoms of the amide carbonyl groups of the pendant arms.