Coordination chemistry of some new Mn(II), Cd(II) and Zn(II) macrocyclic Schiff base complexes containing a homopiperazine head unit. Spectral, X-ray crystal structural, theoretical studies and anticancer activity

Abstract

Here we report a number of novel macrocyclic Schiff base complexes with a homopiperazine skeleton. These symmetrical pentaaza macrocyclic Schiff base complexes were prepared via a template approach, based on the condensation reaction of an amine containing homopiperazine moiety and 2,6-diacetylpyridine or 2,6-pyridine dicarboxaldehyde in 1:1 mol ratio in the presence of Cd(II), Mn(II) and Zn(II) metal ions. These Schiff base complexes were characterized by elemental analyses, FT-IR, mass spectrometry and, in the cases of diamagnetic Zn(II) and Cd(II) complexes, 1H and 13C NMR spectroscopy. As well, the structures of [Mn(L1)(CH3OH)(ClO4)]ClO4 and [Cd(L2)(H2O)2](ClO4)2 have been determined by X-ray structural analyses, where the L1 and L2 are the products of the reaction of the new amine with 2,6–Pyridinedicarboxaldehyde or 2,6–diacetalpyridine, respectively. The coordination environment of the metal atoms in both of these complexes is best described as a distorted pentagonal bipyramid. The cytotoxic activities of these new complexes were also examined. The potency of complexes to induce cell death was screened on A2780, U37 MG, and H1299 cell lines, compared to doxorubicin which was used as a control. The results reveal that in some cases, the cytotoxic activity of complexes was stronger than that of doxorubicin as standard. Also, the bonding situation in the complexes, were analyzed by NBO and energy-decomposition analysis (EDA) and EDA-NOCV analysis.