Synthesis, spectroscopic and thermal studies of biologically active complexes containing a macrocycle derived from piperazine and pyridine-2,6-dicarboxylic acid

The transition metal complexes comprising a macrocycle ligand 1, namely N,N'-diethylpiperazin-ylpyridine-2,6-dicarboxylate, are synthesized. This macrocycle is prepared from the reaction of dipotassium salt of pyridine-2,6-dicarboxylic acid with 1,2-dibromoethane and piperazine. The reaction of macrocyle 1 (L) with CrCl3.6H2O, FeCl3.6H2O, CuCl2.2H2O and ZnCl2.2H2O yielded the complexes with the general formula [M(L)Cl2]Cl (where M = Cr(III) 2 and Fe(III) 3) and [M(L)Cl2] (where M = Cu(II) 4 and Zn(II) 5), respectively. The analysis of IR,1H- and 13C-NMR spectral data of the complexes suggest that macrocycle 1 is bonded to metal ions through two oxygen atoms of ester moiety, and the two nitrogen atoms of amino groups. The electronic spectral data of these complexes are in good agreement with the octahedral coordination of the metal ions. The splitting energy and Racah parameter is calculated to be 15,748 and 719 cm-1 for the Cr(III) complex 2. The splitting energy of 17,326 cm-1 is obtained for the Cu(II) complex 4. The thermal analysis revealed that no water molecules of hydration and coordination in structure of complexes. In among of these complexes, the Cu(II) 4 and Zn(II) 5 complexes showed good antibacterial and antifungal activities.

Piperazine; 1,2-Dibromoethane; Splitting energy; Thermal analysis; Antimicrobial studies; Pyridine-2,6-dicarboxylic acid