Zinc, copper and nickel complexes of a macrocycle synthesized from pyridinedicarboxylic acid: A spectroscopic, thermal and theoretical study

The metal(II) ion complexes of a pentadentate macrocycle 1, namely 3,12-dioxa-6,9,18-triazabicyclo[12.3.1]octadeca-1(18),14,16-triene-2,13-dione are synthesized. This macrocycle is prepared from the reaction of dipotassium salt of 2,6-pyridinedicarboxylic acid with ethylenediamine and 1,2-dibromo­ethane. The reaction of 1 (L) in methanol with MCl2.xH2O gave complexes with the general formula [M(L)Cl2] (where M= Ni(II) 2, Cu(II) 3 and Zn(II) 4, respectively). The analysis of IR, 1H- and 13C-NMR spectral data of all complexes propose that 1 is bonded to metal(II) ions through a nitrogen atom of pyridine ring, two nitrogen atoms of amine groups and two oxygen atoms of ester moieties. The thermal analysis indicated that there are no water molecules of hydration or coordinated in the structure of the complexes. Among these complexes, the Cu(II) 3 complex demonstrated good antibacterial and antifun­gal activities. The molecular geometry, AIM atomic charge and frontier mole­cular orbitals of the compounds are investigated theoretically using DFT method. Based on the theoretical data of these complexes represented, a bipyr­amidal pentagonal arrangement can be envisaged in such a way that the N3O2 pentadentate donor sites form the planar pentagonal base of the bipyramid and the two Cl atoms occupy the vertexes.