Synthesis, characterization and anti-microbial activity of a novel macrocyclic ligand derived from the reaction of 2,6-pyridinedicarboxylic acid with homopiperazine and its Co(II), Ni(II), Cu(II), and Zn(II) complexes

The preparation of a novel macrocyclic ligand (1), N,N′-diethylhomopiperazinyl,2,6-pyridinedicarboxylate and its Co(II), Ni(II), Cu(II), and Zn(II) complexes are described. The ligand was prepared in EtOH from the reaction of dipotassium salt of 2,6-pyridinedicarboxylic acid with 1,2-dibromoethane in the presence of homopiperazine.Reaction of macrocyclic ligand (1) in EtOH with CoCl2.6H2O, NiCl2.6H2O, CuCl2.2H2O, and ZnCl2·2H2O yielded the complexes with the general formula [M(L)Cl2] {where M = Co(II) (2), Ni(II) (3), Cu(II) (4), Zn (5), respectively}. The analysis of IR, 1H and 13C NMR spectral data of macrocyclic ligand (1) and its Zn(II) complex (5) together with their molar conductivity values, and the magnetic moments of the complexes suggest that the macrocyclic ligand (1) is bonded to metal(II) ions through two oxygen atoms of ester moiety and the two nitrogen atoms of homopiperazine ring. The electronic spectral data of these complexes in DMSO are in good agreement with the octahedral coordination of M(II) ions. The ligand field parameters for these complexes, i.e. splitting energy and Racah parameter were calculated to be 14,945 and 673 cm−1 for the Co(II) (2), 16,260 and 774 cm−1 for the Ni(II) (3) complexes respectively. The spliting energy of 17,262 cm−1 was obtained for the Cu(II) complex (4).