1H-NMR study of the stoichiometry and stability of the Ba2+, Sr2+, Hg2+, Pb2+, K+, Ag+, and Tl+ complexes with a new macrocyclic diamide in acetonitrile–nitrobenzene solvent mixture

Abstract

Proton NMR technique was utilized to study the complexation reactions of a new macrocycle diamide with Ba2+, Sr2+, Hg2+, Pb2+, K+, Ag+, and Tl+ ions in % 50 (w/w) acetonitrile–nitrobenzene binary mixture. In all the cases, the chemical shifts of the single NMR signals due to the –O–CH2–CH2–O– and Ph–O–CH2– groups of the ligand were determined at 300 K. The exchange between free form of the macrocycle (I) and its complexes was fast on the NMR time scale and just a single population average 1H signal was observed. Formation constants of the resulting 1:1 complexes were determined by computer fitting of the chemical shift–mole ratio data. The stabilities of the resulting 1:1 complexes varying in the order Ba2+ > Sr2+ > Hg2+ > Pb2+ > Ag+ > K+ > Tl+ were determined. For two singlet groups of ligand (I) (Ph–O–CH2– and –O–CH2–CH2–O–), the values of the formation constants which were obtained from data fitting were found to be similar, but shift of the signal for Ph–O–CH2– group was larger than for –O–CH2–CH2–O– group. The theoretical studies on the structures and the energetic data of the five conformers of ligand macrocycle (I) and the complexes with Ba2+, Sr2+, Hg2+, Pb2+, Ag+, K+, and Tl+ have been performed by DFT-B3LYP/6-31G* method for ligand (I) and QM-PM6 method for the complexes. The comparison of the experimental and theoretical data with respect to the formation constants and the structures of the complexes have shown good agreement.